Dr.habil. Dr. Seronei arap Chelulei Cheison: palatants

Showing posts with label palatants. Show all posts

Thursday, 22 October 2026

The Invisible Palatant: How Processing Shapes Petfood Palatability

The Invisible Palatant. The Friday Conversation No. 14. A hand holds a handful of warm, uncoated kibble on a petfood production line, with raw meat and pulses, an extruder and a coating drum behind, finished food in a bowl, and a dog and cat watching.

The Invisible Palatant. By the time the palatant reaches the coating drum, the food already has a smell, a texture and a sensory history. What the animal encounters was being shaped long before the final coating, and no single stage can claim all the credit.

Movement I

BEFORE THE DRUM

Stand at the end of the line in a petfood plant, past the extruder and the dryer, before the coating drum, and stop the belt for a moment. Reach in and take a handful of the kibble as it comes off the dryer. It is warm, dry, pale, finished in shape but not yet in anything else. Nothing has been sprayed on it. Nothing has been dusted over it. The fat, the palatant, the coating the industry thinks of as the flavour, all of that is still waiting a few metres downstream, in the drum the pieces have not yet reached.

Now put the handful to your nose.

It smells of something. Not of nothing, not of a blank pellet waiting to be given a character, but of something already: a warm, toasted, faintly meaty, faintly cereal smell that is unmistakably food. No one sprayed it on. It arose, somewhere back along the line, out of the raw materials and the cooking, and there it sits in your palm, a finished aroma on an unfinished food, before the part of the factory whose whole job is flavour has so much as touched it.

That is the fact this essay begins from, and it is stranger than it first sounds. We have organised much of the business of petfood around a convenient division: the base supplies the nutrition, the coating supplies much of the attraction. It is a useful division of labour, and no one who works in it imagines the base is odourless. But the division shapes how we speak and where we look, and the handful in your hand shows why it is not the whole account of the food. Because the base, before any coating, already smells. It already has a taste waiting in it. It already carries, written into its cooked and dried body, a sensory character the animal will meet whether or not another thing is ever added to it.

The invisible palatant is not something the factory adds. It is what the factory has already done.

Which turns the usual question inside out. We are used to asking what a palatant brings to a food. The handful of naked kibble asks the reverse. If the food already smells of something before the palatant arrives, then what is the palatant arriving at? It is not coating a blank. It is landing on a food that has already been made to smell and taste of something by everything that happened before, and whatever it adds will mix with, lean on, or work against a character that was there first.

And if that is so, a harder question follows, the one this Conversation is really about. When an animal empties one bowl and leaves another, and both foods wore the same coating, we reach by habit for the coating to explain the difference. But the coating was the last thing to happen to either. How much of what the animal was answering to had already been settled upstream, in the cooking, before the drum, before the stage we credit with flavour ever entered the story?

Keep the handful. We are going to follow it back up the line.

Movement II

THE FACTORY IS A KITCHEN

Follow the smell back and it leads where every good smell in a kitchen leads: to heat, and to what heat does to food.

For all its scale and steel, a petfood plant is doing something a cook would recognise. It takes raw materials, meats, grains, fats, and it cooks them. The extruder is an oven and a pan at once, driving heat and pressure through the mix; the dryer finishes the work. And cooking, whether in a pan or in a barrel the length of a room, is not a neutral warming. It is chemistry. The heat sets the food's own components reacting with one another, and out of those reactions come things that were not in the raw mix at all, among them the smells.

The chief of these has a name, though the cook who browns an onion or sears a steak has never needed it. When the amino groups carried by the food's proteins and their smaller building blocks meet reducing sugars under heat, a cascade of reactions begins. Some of what it makes is colour, the browning of a crust; some of it is aroma, the roasted, nutty, meaty and savoury notes we know from cooked food. It is the chemistry of the crust on bread and the sear on a steak, and it is running, at industrial scale, inside the machine that made the handful in your palm. No one reached for a bottle of meaty flavour. The cooking made one, out of the food's own flesh and grain.

The fats take their own part, reacting under heat into notes of their own, some the warm richness a carnivore reads as food, some, pushed too far, the first edge of the rancid. And moisture sits quietly behind all of it, as the last Conversation argued, deciding what can react and how, so that the water in the mix is not a bystander to the cooking but one of the hands shaping what the cooking makes. The point, for now, is only this: by the time the pieces reach the dryer, a great deal of sensory chemistry has already happened, unbidden and unbottled, written into the food by the plain fact that it was cooked.

But there is an awkward question sitting in all this. If the cooking makes the flavour, why might a dog find a piece of raw meat worth crossing a room for, with no cooking at all? Why might a cat approach raw flesh with an interest no coating drum was ever required to produce?

Because the cooking did not begin with nothing. Meat arrives already carrying its own chemistry, its own taste-active substances, its own quiet history of change since the animal it came from died. Heat can release what was bound inside it, transform what was already there, build compounds that did not exist before, and spend some of the signals the animal would otherwise have met.

Cooking is an author of flavour, but not its first author.

So the raw meat corrects something the factory makes easy to forget. The line we have been following back does not stop at the dryer, or even at the raw mix. It runs to the ingredient itself, which arrived already able to taste of something. Processing changes what was already possible; it does not conjure it from nothing.

And here it would be easy to draw exactly the wrong conclusion. If the cooking generates flavour, then surely more cooking, more reaction, more of that brown and savoury chemistry, makes a better food. It does not, and the error is worth naming because it is so tempting. Push the reactions too hard and the roasted turns scorched, the savoury turns acrid and bitter, and the nutrition suffers in the bargain, the building blocks the animal needed spent on compounds no one wanted. A reaction can make a new smell without making a better one. More chemistry is not more palatability; it is only more chemistry.

To generate a flavour compound is not to earn a preference.

Which is the discipline this movement insists on, against its own enthusiasm. It is genuinely remarkable that a food can cook itself a smell. But the machine that generates a thousand new compounds has not thereby chosen the ones an animal wants. Of all that chemistry, which did the dog or the cat actually ask for? We cannot read a preference off a chromatogram. The cooking tells us what was made. It does not tell us what the animal, with its own and different biology, will seek. That verdict was never the factory's to give.

So the handful in your hand is not a blank that flavour will later be added to. It is already the work of a kind of cooking, carrying a character the cooking built and the cooking could just as easily wreck. Which raises the question the next movement turns on. If the base food already has a character of its own, what happens when the coating finally arrives and meets it?

Movement III

THE SUBSTRATE HAS A MEMORY

Now let the pieces reach the drum, and let the coating arrive at last.

In the tidy division of labour, this is the moment flavour is supposed to happen. The fat and the palatant go on here, the same measured amount to every batch, and the industry speaks of the result as though the coating carried its performance within itself, a fixed quantity of palatability poured evenly over whatever passes through. Send the same coating down the line at the same rate and you should, on that picture, get the same food.

You do not, and the reason is the whole of this movement. The coating does not land on a neutral surface. It lands on the food we have just followed out of the kitchen, a food with a structure the cooking gave it, a surface the drying left, and an aroma the reactions already built. The base is not an empty page the coating writes on. It is a page already written, and what the coating becomes depends on what was there to receive it.

Consider only what the structure can do. A piece left more open and porous by its cooking may take the coating in and hold it, releasing it slowly from within, where a denser, more closed piece may carry more of the same coating on its surface, exposed and quicker to give itself up. That is one way a base can shape what the coating delivers, not a rule, and real pieces rarely sort themselves so neatly into kinds. But wherever such a difference runs, the identical spray, the identical amount, becomes a slower, deeper thing on one food and a quicker, brighter one on another. The coating specification alone might not tell them apart. The drum applied the same material to both. The food did not receive it in the same way.

And the aroma the base already carries does not stand politely aside while the coating speaks. The base's smell and the coating's meet, and where they meet the newcomer can be lifted by what was already there, or lost in it, or set against it. A savoury coating laid over a warm, savoury base is not the same event as the same coating laid over one the cooking left flat, or scorched. The coating's contribution is real, but it is never delivered into silence. It is delivered into a sound the food was already making.

A palatant does not carry its performance alone. It performs on the food it is given.

So the thing the industry treats as a fixed property turns out to be a meeting. The result at the bowl is not the base plus the coating, separate quantities laid side by side and summed. It is what the two did to each other, and that cannot be split cleanly back into a share for each. It is the same lesson this series has kept arriving at from every direction, that a signal has no worth on its own, only in the thing that receives it, carried now one step further back, into the food itself: the coating's worth, too, is less its own than it looks, decided in large part by the base that will hold it, release it, or drown it.

Which turns the usual verdict into a question. When a food is emptied and another, wearing the very same coating, is left untouched, we say the coating on the second failed. But did it? Or did it do exactly what it does, on a base that received it differently, so that the thing we blamed last was shaped by the thing we never thought to look at first? The palatant did not underperform in the abstract. It performed, as it always does, on the particular food it was given, and that food had a memory the sheet never recorded.

So before we ask who gets the credit, we have to admit the work cannot be cleanly divided. Which is exactly where the factory's neat departments begin to strain.

Movement IV

WHO GETS THE CREDIT?

A factory runs on division. The thing that lets a plant make tonnes of a complex food is that no one person makes it. The work is cut into parts, and each part is handed to someone who is very good at it.

One company grows and sells the protein, another the fat, another the grains. A process engineer owns the cooking, and knows that machine the way a chef knows a stove. A formulator sets the recipe and its targets. A palatant developer builds the coating and understands, better than anyone else in the chain, how it behaves. These are not naive people. Ask any of them and they will tell you that the parts interact, that the coating depends on the base, that the cooking shapes the smell. The knowledge is there, held in good hands, all along the line.

And yet something gets lost in exactly the seam that makes the whole thing work. Because each of these experts owns a part, and not one of them owns the animal's experience. The dog does not eat the supplier's protein, or the engineer's cooking, or the developer's coating. It eats the single thing all of them made together, and that thing belongs, in the end, to no department.

The factory is divided into departments. The animal is not.

Which makes the simplest question, whose result is it, strangely hard to answer. The last movement showed why the result cannot be split into clean shares, a quantity from the base and a quantity from the coating laid side by side and summed. If the contributions are not separable in the food, they are not separable in the credit either. The animal's verdict is real, but it is a verdict on the whole, and it does not come itemised. It will not tell you how much was the protein, how much the cooking, how much the drum.

So when a food performs, or fails to, the pull is always toward the same answer. We credit, or blame, the coating. Not because anyone believes it acted alone, but because it is the most visible stage and the easiest to change. The ingredients are contracted months ahead, the cooking is fixed in steel, the recipe is signed off. The coating is often among the last levers still available to adjust, and therefore among the first we reach for, so it becomes the stage we change, and in changing it we quietly hand it a responsibility the food never gave it alone.

The last thing added is the first thing blamed.

And there is a sharper turn of the same screw. Processing can remove sensory signals as readily as create them, and not every change will favour the animal's response. Could the coating sometimes be praised for recovering something an earlier stage quietly removed, the last operation credited for repairing the work of one no one examined? The possibility is worth sitting with, even if the share each stage took cannot be read off the finished food.

This is not a charge of ignorance. The specialists understand the interactions better than the essay does. It is a charge against the shape of the thing, against the way a problem that lives in the relationship between stages comes to rest on whichever stage is nearest to hand. The division of labour that makes the factory possible is the same division that scatters the authorship of the result across boundaries, between companies, between departments, between the people who built the base and the people who coated it, so that when the animal turns from the bowl, the cause may sit in a seam no single party was ever asked to watch. Where, then, should the responsibility rest?

That is the uncomfortable place this movement leaves us. The food is a joint work, and the responsibility for how it tastes to the animal is joint too, distributed along a chain that was organised, for every good reason, to be divided. We know how to assign credit to a stage. We are far less practised at assigning it to a relationship.

Which leaves only the one party who never divided anything, and never could: the animal, at the bowl, meeting all of it at once.

Movement V

THE ANIMAL EATS THE WHOLE FACTORY

Set the bowl down, and watch what happens to all of it.

The factory spent the length of a building keeping its work in order. The supplier's ingredient, the engineer's cooking, the structure the drying set, the smell the reactions built, the coating from the drum, each made in its own place, by its own hands, booked to its own account. And then the animal lowers its head and, in a single mouthful, undoes every division the factory was built on. It does not taste the protein, then the cooking, then the coat. It tastes a food. All of it at once, with no seam anywhere.

The animal does not taste a department. It tastes a food.

This is where the invisible palatant stands fully revealed, and it was never a thing at all. It is everything the factory had already done by the time the coating arrived: the aroma the cooking drew out of the raw mix, the structure that would hold the coat or shed it, the character written into the base before the drum was reached. The visible palatant, the one on the invoice, the one the drum applies, is real and does real work. But it lands into a performance already under way, and what the animal answers to is both at once, the added and the already-there, which it has no way of telling apart and no reason to try.

So the lesson this series has kept reaching lands, at last, at the scale of the plant. Palatability is not sealed in the coating, any more than in the recipe, the molecule, or the bowl; it is assembled, each time, in the animal, out of everything the food turns out to be. Which means the work of making a food an animal wants was never the last stage's alone. It began at the first, in the choice of what to cook and how.

And if that is so, one habit is worth retiring. Why do we still speak as though flavour begins at the drum, as though the food before it were a blank waiting to be made worth eating? The handful we took off the dryer, warm and already smelling of something, said otherwise on the first page. The food was telling its sensory story from the beginning. The coating only wrote the last line of it.

We divide the factory into operations. The animal encounters their consequences together.

References

1. Martins, S.I.F.S., Jongen, W.M.F. & van Boekel, M.A.J.S. (2000). A review of Maillard reaction in food and implications to kinetic modelling. Trends in Food Science & Technology 11(9-10):364-373. doi:10.1016/S0924-2244(01)00022-X

2. Mottram, D.S. (1998). Flavour formation in meat and meat products: a review. Food Chemistry 62(4):415-424. doi:10.1016/S0308-8146(98)00076-4

3. Tran, Q.D., Hendriks, W.H. & van der Poel, A.F.B. (2008). Effects of extrusion processing on nutrients in dry pet food. Journal of the Science of Food and Agriculture 88(9):1487-1493. doi:10.1002/jsfa.3247

4. Guichard, E. (2002). Interactions between flavor compounds and food ingredients and their influence on flavor perception. Food Reviews International 18(1):49-70. doi:10.1081/FRI-120003417

5. Koppel, K. (2014). Sensory analysis of pet foods. Journal of the Science of Food and Agriculture 94(11):2148-2153. doi:10.1002/jsfa.6597

6. Aldrich, G.C. & Koppel, K. (2015). Pet food palatability evaluation: a review of standard assay techniques and interpretation of results with a primary focus on limitations. Animals 5(1):43-55. doi:10.3390/ani5010043

7. van der Vyver, Y., Paul, A., Blecker, C. & Danthine, S. (2026). Gaps and controversies in feline food palatability. Animals 16(17):2721. doi:10.3390/ani16172721

About the Author

Dr. rer. nat. habil. Dr. Seronei Chelulei Cheison is the founder and Chief Executive Officer of Sinonin Biotech GmbH, where he works with petfood companies on palatant sourcing strategies, the innovation of palatability enhancers, and the design of palatability assessment. A trained food enzymologist, he led alternative protein and palatant development at Mars Petcare before founding Sinonin, and his research on protein chemistry spans two decades, a doctorate from Jiangnan University, and a habilitation from the Technical University of Munich.

Sinonin Biotech GmbH is a partner in the ZEST project (Grant Agreement No. 101157382) and the PROSCALE project (Grant Agreement No. 101288362), both funded by the Circular Bio-based Europe Joint Undertaking (CBE JU) under the European Union's Horizon Europe research and innovation programme. Views and opinions expressed are those of the author only and do not necessarily reflect those of the European Union or CBE JU. Neither the European Union nor the granting authority can be held responsible for them.

Thursday, 1 October 2026

A Cat Is Not a Big Dog: Why Petfood Palatability Is Species-Specific

A Cat Is Not a Big Dog. The Friday Conversation No. 11. A cat and a dog facing a single food bowl, with two different streams of aroma and taste signals rising from it toward each animal.

Why petfood palatability is species-specific. A cat is not a small dog in the liver, where a drug tolerated by one species can be dangerous to the other. This essay asks whether we have remembered that at the bowl.

There is a tablet in almost every home that makes the point rather brutally. Paracetamol is a familiar medicine for people, and can be used therapeutically in dogs under veterinary supervision. In cats, the same molecule can be dangerously toxic. The difference is not in the tablet. It is in the animal receiving it.

Veterinary medicine learned this a long time ago. Species is not a matter of scale. A cat is not a dog made smaller, any more than a dog is a wolf brought indoors and shrunk to fit the sofa. Their biology diverges in places that matter, and what one species can metabolise, tolerate or use safely cannot simply be carried across to the other. A cat's liver, in this instance, lacks the machinery a dog's relies on to break the drug down and clear it, so what leaves one animal quietly builds up in the other. We accept the lesson readily when the consequence is toxicity.

At the bowl, we have sometimes been less careful.

A cat and a dog can be offered the same food, carrying the same volatile compounds, the same peptides and amino acids and nucleotides and fats. On the analysis sheet the stimulus is identical. Biologically it is not, because it arrives at two different sensory systems, shaped by two different evolutionary histories, equipped with different receptors, different feeding behaviours and different expectations of what a meal is supposed to signal. The formulation may be identical. The sensory information arriving at the brain is not.

So this Conversation begins with a proposition that veterinary medicine already knows by heart, and that petfood palatability has been slower to take seriously. A cat is not a big dog. Not in the liver, where the difference can be measured in survival. And, this essay will argue, not at the bowl either. Which leaves a question worth carrying through everything that follows: when a cat turns from a food that a dog accepts, what exactly have we learned, about the food, or about the difference between the two animals we offered it to?

Movement I

SAME BOWL, DIFFERENT ANIMAL

Start not with the senses but with the two histories that shaped them, because the difference between a cat and a dog at a bowl is older than either animal's tongue.

The dog descends from a pack hunter and scavenger, an animal that ate when it could and often could not, that pulled down large prey together and gorged, then went without. That past is written into the dog we feed, an animal broadly built to take a large meal quickly and to wait a long time for the next, tolerant of a bowl that arrives once or twice a day, and inclined to try what it finds, because a scavenger that samples widely eats more often than one that does not. The cat descends from something quite different, a solitary hunter of small prey, an animal that caught a mouse, ate it, and hunted again, many times across a day and a night. It was never a gorger, because a mouse is not a feast, and its body records the difference at the plainest level. A cat's stomach is small, holding only a few hundred millilitres, restricted enough that the natural pattern is many small meals rather than a few large ones. In the wild the cat takes something like a dozen or more tiny feeds across the day, five to seven grams at a time, little and often, the rhythm of the hunt.

The dog was built to gorge and wait. The cat was built to graze the day in small returns.

Hand these two animals the same bowl, on the same once-a-day schedule, in the same quantity, and something quietly odd has happened, though it is so ordinary we never notice it. We have asked the cat to eat like a dog. Much of what frustrates the owners of cats, the food left half-eaten and returned to through the day, the refusal of a large single serving, the picking and grazing that reads as fussiness, is the cat doing exactly what it was built to do at a bowl designed around the dog's pattern rather than its own. And the cat is warier of the new than the dog, because a specialist hunter of fresh prey is safer treating the unfamiliar with suspicion where a scavenger profits from trying whatever it finds. So it is worth asking, before we call the cat difficult, whether we have ever actually offered it a cat's meal, or only a dog's meal that a cat was expected to accept.

The difference runs deeper than schedule and quantity, down to what each animal is trying to achieve when it eats. Left to choose freely among foods, neither animal simply eats what tastes best. Each eats toward a target, a particular balance of protein and fat that suits its biology, and the two targets are not the same, the dog's leaning toward fat and the cat's toward protein, close to the composition of the prey it evolved to catch. The striking part is what happens when taste and target disagree. In studies where cats were offered foods of different flavours and different nutrient content, they chose at first by flavour, exactly as we would expect, and then, over the following days, learned the compositions and shifted their choices to reach their nutritional target, overriding the very flavours that had won the first meal. Read that slowly, because it unsettles a comfortable assumption. For the cat, in the end, palatability can lose to need. The tastiest option does not necessarily win if it pulls the animal away from where its body is trying to go, and that is not a fact one could ever recover from a single first-choice test.

It is worth conceding at once that the line is cleaner than nature is. A Chihuahua is not a Great Dane, and on several of these measures a tiny toy dog with a small stomach and a delicate appetite sits closer to a cat than to a mastiff that bolts a bucket of food and looks up for more. Breed, size, age and temperament all move an animal along these axes, and the within-species range can be as wide as the gap between species. The claim is not that every cat differs from every dog on every count. It is that the cat, as a type, is built along a different line from the dog, as a type, and that the differences are biological and consistent rather than matters of mood. So before we ask why the cat is harder to please, a prior question is worth holding: harder to please than what, and measured against whose idea of a meal?

Movement II

THEY DO NOT TASTE THE SAME WORLD

If the two animals were shaped by different pasts, the deepest mark that past has left is on the senses that meet the food, and here the differences are not of degree but of kind. Set the same bowl before a cat and a dog and, at the level of the nerves, two different foods are being received.

Begin with the plainest divergence, which is also the one most easily forgotten. The cat cannot taste sweetness. The receptor that detects sugars, which the dog carries and responds to, exists in the cat only as a broken gene, present in the genome but silent, switched off across evolutionary time in an animal that never ate anything sweet. This is not a mild preference against sweet things. It is an absence of the signal altogether, in the way a colour-blind eye receives nothing where another eye receives red. A sweet note that a dog leans toward reaches the cat as nothing at all. And it would be a mistake to fill that silence with our own vocabulary, because the risk throughout this territory is that we describe the animals' senses in the words of ours. Both cats and dogs respond to the savoury, meaty quality we call umami, but they do not reach it by the same route; the molecules that trigger it most strongly in a cat, abundant in fresh animal tissue, are not the same ones, or in the same proportions, that trigger it in a dog. The word is the same. The chemistry the word points to is not.

The formulation may be identical. The sensory information arriving at the brain is not.

If that is true of the one taste the two animals seem to share, what should we expect of a food built on the human assumption that savoury is savoury and sweet is a virtue, to whichever animal happens to eat it? The cat also judges with a strikingly small set of taste instruments, a few hundred taste buds where a dog has several times as many, and it would be easy and wrong to read that as a fainter version of the dog's palate. It is not weaker. It is narrower and more sharply tuned, an instrument built to make a small number of distinctions that matter to a hunter and to ignore much that does not. And because the palate gives it so little to work with, the cat throws the weight of the decision onto its nose. Even here the easy comparison misleads. The dog carries more scent receptors overall, and on that number alone one would call it the better-nosed animal, but the two noses are built for different jobs. The dog's is built to detect and to track, to find a faint scent across a field. The cat's is built to discriminate, to tell one close smell from another, and it carries several times as many of the specialised receptors that do that fine sorting. The dog's nose asks where is it. The cat's asks what exactly is it, and is it right. And because the cat can barely taste, that discriminating nose is not a helper to the meal decision. It is the meal decision.

The dog's nose is built to find the food. The cat's is built to judge it.

Then, if the food passes the nose, comes the mouth, and the cat's mouth is a set of prey tools the dog's is not. A dog's jaw can move sideways and grind; a cat's cannot. The feline jaw is close to a pure hinge, and the teeth behind it are blades, not millstones, shaped to shear meat from a carcass rather than to crush and chew. A cat has fewer teeth than a dog and none of the flat grinding surfaces, and so it does not really chew in the sense we mean; it slices and swallows, or rolls a piece to the side to break it. Even the tongue is a different tool, covered in backward-facing spines of keratin, the same material as the claws, a rasp built to strip meat from a bone where a dog's tongue is smooth. Salt, which flatters the human palate and is useful in the dog, is close to dead in the cat, an obligate carnivore that ate whole prey and was never short of sodium. At point after point, the same food is not the same food. It is warmed or cooled into a different aroma, met by a different palate, judged by a different nose, and handled by a different mouth. So the question that closes this movement is not whether cats and dogs differ. It is a harder one. How did we ever persuade ourselves that a signal built to please one of them would arrive, unchanged, at the other?

Movement III

THE PALATANT IS NOT THE MESSAGE

There is a way of speaking about palatability that treats it as a property a food simply has, a quality you can build into a recipe and then measure, the way you build in protein and then measure it. On that view a palatant is a thing you add to make a food more palatable, and palatability is what you have added. It is a comfortable picture, and it is wrong, and the two animals we have just been comparing are what expose it. Because here is the question the comparison forces. If the molecule leaving the bowl is the same, and the animal receiving it is not, where exactly does the palatability live?

Consider what a palatant actually is. It is a collection of signals, chemical and physical, aromas and tastes and textures, assembled to be detected. But a signal is not a message until something receives it, and detection is only half of what is happening at the bowl. The other half is interpretation, and interpretation belongs to the animal, not to the food. A molecule that lands on a receptor the cat does not have sends nothing. A molecule that lands on a receptor the cat has, but reads through the biology of a fresh-kill hunter, may mean something quite different to the cat than the same molecule means to the dog. The palatant does not carry its meaning inside it, sealed and portable, the way a number is carried on a specification sheet. Its meaning is made, each time, in the meeting between the signal and the animal that receives it. We said it of the drug at the start, and it holds just as firmly here. The difference is not, in the end, in the palatant. It is in the animal receiving the signal.

There is no such thing as a palatable molecule. There is a molecule, a receptor, an animal, and a response.

An earlier Conversation reached the same place from a different door. It argued that palatability does not reside in the food alone, that a diet is not palatable or unpalatable in the abstract but only to a particular animal, in a particular state, on a particular day. That was said of the individual patient, of how illness and appetite and memory change what a food means to the one animal in front of the bowl. This is the same truth read at the level of the species. If palatability does not reside in the food for a single sick cat, it does not reside in the food across the gulf between a cat and a dog either. It never lived in the molecule. It lives in the response, and the response is the animal's to give.

This is why the comfortable picture fails, and why it matters that it fails. If palatability were a property of the food, then a food made more palatable would be more palatable to whatever ate it, and the species of the eater would be a detail. But if palatability is a response, assembled freshly in each animal from signals its own biology decides how to read, then the species is not a detail at all. It is the thing that decides what the signals mean. So a food developed until it performs beautifully for one animal has been tuned, precisely, to one animal's way of reading it. What has it been tuned to, for the other? And how would we know, if the only animal we asked was the one it already suited?

Movement IV

ONE FACTORY, TWO BOWLS

None of this is news to the people who make pet food. Of course the industry develops separately for cats and dogs; of course it knows the two animals differ. The question is subtler, and it is about assumption rather than intent. When a discipline grows up around the easier subject, its habits form around that subject, and the habits travel quietly into the harder work without anyone deciding they should. The dog is the more forgiving eater, the one whose acceptance is simpler to win and simpler to read, and a great deal of what we know about testing food, about what a good result looks like and how to interpret a bowl, was learned where it was easiest to learn. The risk is not that we treat the cat as a dog on purpose. It is that a canine logic, built where the animal was accommodating, becomes the default logic, and is carried into feline work as though it were neutral.

Nowhere does this matter more than at the frontier the rest of this series keeps returning to, which is the replacement of familiar animal ingredients with new ones. When a formulator sets out to replace chicken with a protein from a fungus, an insect, a microbe or a plant, it is tempting to describe the task as swapping one protein for another. But a protein is never only a protein. It arrives with a whole constellation around it, a particular set of amino acids and peptides, of nucleotides and volatile compounds, of fats and physical characteristics, and that constellation is precisely what the animal's senses read. Change the source and you change the constellation, and you are no longer presenting the same message to be received. You are presenting a different one, to two different sensory systems, each of which will decide for itself what it means.

A protein is never only a protein. It is the whole constellation the senses read.

And here the species divide turns from a matter of biology into a matter of consequence. Suppose the new protein is tested and accepted by dogs, and performs well. That is a real result, and a welcome one. But when a palatant performs beautifully in dogs, what exactly have we learned about cats?

When a palatant performs beautifully in dogs, what have we learned about cats?

Less than we would like. The dog, with its broader tolerances, its functional sweet sense, its more forgiving nose and its scavenger's willingness, is the animal most likely to accept a substitution and least likely to notice what the substitution lost. A replacement that satisfies the dog has cleared the lower bar. Whether the same replacement has reconstructed, for the cat, the specific chemical world its narrow and exacting biology is tuned to detect, is a separate question, and the dog's acceptance does not answer it. This is why the palatability of alternative proteins is so easily underestimated. It looks like one problem, solved once the animals eat. It is at least two problems, and the one we are more likely to have solved is the one that was easier to begin with.

A replacement the dog accepts has cleared the lower bar. The cat's bar is a different question.

Step back, at the end, and look at the whole arrangement from the factory end of the chain. We put a cat and a dog under the same roof, call them both pets, formulate complete foods for both, coat those foods with things meant to make them desirable, and measure what disappears from the bowl. From that vantage it is natural to see two versions of a single problem, palatability, to be solved with one set of tools and confirmed with one kind of test. Evolution did not see two versions of one problem. It built two different animals, from two different pasts, reading the same bowl through two different sets of senses, wanting two different things from a meal and defending them in two different ways. A cat is not a small dog in the liver, where the wrong dose finds it out. It is not a small dog at the bowl either. And perhaps palatability, if it is to mean anything precise, has to begin not with the food, and not with the factory, but with the animal we are actually asking to eat.

References

1. Court, M.H. & Greenblatt, D.J. (2000). Molecular genetic basis for deficient acetaminophen glucuronidation by cats: UGT1A6 is a pseudogene, and evidence for reduced diversity of expressed hepatic UGT1A isoforms. Pharmacogenetics 10(4):355-369. doi:10.1097/00008571-200006000-00009

2. Li, X., Li, W., Wang, H., Cao, J., Maehashi, K., Huang, L., Bachmanov, A.A., Reed, D.R., Legrand-Defretin, V., Beauchamp, G.K. & Brand, J.G. (2005). Pseudogenization of a sweet-receptor gene accounts for cats' indifference toward sugar. PLoS Genetics 1(1):27-35. doi:10.1371/journal.pgen.0010003

3. McGrane, S.J., Gibbs, M., Hernangomez de Alvaro, C., Dunlop, N., Winnig, M., Klebansky, B. & Waller, D. (2023). Umami taste perception and preferences of the domestic cat (Felis catus), an obligate carnivore. Chemical Senses 48:bjad026. doi:10.1093/chemse/bjad026

4. Lei, W., Ravoninjohary, A., Li, X., Margolskee, R.F., Reed, D.R., Beauchamp, G.K. & Jiang, P. (2015). Functional analyses of bitter taste receptors in domestic cats (Felis catus). PLoS ONE 10(10):e0139670. doi:10.1371/journal.pone.0139670

5. Young, J.M., Kambere, M., Trask, B.J. & Lane, R.P. (2005). Divergent V1R repertoires in five species: amplification in rodents, decimation in primates, and a surprisingly small repertoire in dogs. Genome Research 15(2):231-240. doi:10.1101/gr.3339905

6. Montague, M.J. et al. (2014). Comparative analysis of the domestic cat genome reveals genetic signatures underlying feline biology and domestication. Proceedings of the National Academy of Sciences 111(48):17230-17235. doi:10.1073/pnas.1410083111

7. Bradshaw, J.W.S. (2006). The evolutionary basis for the feeding behavior of domestic dogs (Canis familiaris) and cats (Felis catus). The Journal of Nutrition 136(7):1927S-1931S. doi:10.1093/jn/136.7.1927S

8. Hewson-Hughes, A.K., Hewson-Hughes, V.L., Colyer, A., Miller, A.T., McGrane, S.J., Hall, S.R., Butterwick, R.F., Simpson, S.J. & Raubenheimer, D. (2013). Geometric analysis of macronutrient selection in breeds of the domestic dog, Canis lupus familiaris. Behavioral Ecology 24(1):293-304. doi:10.1093/beheco/ars168

9. Hewson-Hughes, A.K., Hewson-Hughes, V.L., Miller, A.T., Hall, S.R., Simpson, S.J. & Raubenheimer, D. (2011). Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. The Journal of Experimental Biology 214(6):1039-1051. doi:10.1242/jeb.049429

10. van der Vyver, Y., Paul, A., Blecker, C. & Danthine, S. (2026). Gaps and controversies in feline food palatability. Animals 16(17):2721. doi:10.3390/ani16172721

About the Author

Thursday, 17 September 2026

Petfood palatability: Why amount eaten under-measures liking

Beyond the Bowl, The Friday Conversation No. 9. An empty pet bowl on a digital scale reading zero grams, 263 grams consumed, with a dog and a cat regarding it.

We measure too little, we discard too much, and we sometimes infer more than the measurement can support.

A family finishes a good dinner and carries the plates to the kitchen. Someone scrapes the last of the bones into a bowl and steps out to the kennel, where two dogs have heard the door and are already on their feet. The bones go over the fence. What follows is not dignified. There is a scramble, a scattering, a low warning growl, a snatched femur carried off at speed and defended against a sibling who wants it more than anything in the world. To watch them is to be in no doubt at all. The dogs love these bones.

Now move a few hundred kilometres to a room where the same enthusiasm is being manufactured on purpose. A commercial food has been developed, refined and tested to the point of exhaustion, precisely to predict that dogs will eat it eagerly and come back for more. And when the trial runs, they do. The bowls come back empty. The numbers are excellent. The food, by every measure the room can produce, is a success.

Both scenes end the same way. An empty vessel and an animal that ate what was there. On the record they look identical, and that is exactly the difficulty. The dogs may truly love those bones. But the scene at the fence cannot tell us how much of what we are watching belongs to the bones themselves, how much to hunger, how much to the brother competing for the same femur, and how much to the simple fact that food has suddenly appeared. If ravening for scraps and clearing a tested bowl leave the same trace, then the trace is holding more than one cause and telling us less than we think. Somewhere underneath the grams eaten is a question the grams cannot answer on their own.

What exactly did we measure?

Movement I

THE EMPTY BOWL

There is an extraordinarily simple instrument at the centre of petfood palatability science. A bowl. Sometimes two. We weigh the food before the animal enters. We put the bowl down. The animal approaches, smells, hesitates perhaps, begins to eat, stops, moves away, comes back, changes bowls, eats again and eventually leaves. We collect what remains and weigh it. Between those two weighings an astonishing amount of biology has happened, and at the end of it we are left with a wonderfully precise number. Grams eaten.

These methods have served the industry well. They are simple, reproducible and commercially meaningful, and if animals consistently eat more of one formulation than another, anyone developing petfood should want to know. I have relied on them, and I would rely on them again tomorrow. The point of this essay is not that the bowl is wrong. It is that the bowl is quiet about most of what it saw.

Because an empty bowl is a powerful commercial signal, and a powerful temptation. A food that goes uneaten has a problem, whatever its nutritional formulation, and I have argued throughout these Conversations that adequacy and acceptance are different problems. But we should be careful about what an empty bowl allows us to conclude, and the care begins with a fact so obvious it is easy to step over. Animals eat because eating is necessary. An animal needs energy and nutrients to stay alive, and hunger exists to make sure it goes and gets them. Feeding therefore sits at an awkward junction between physiological necessity and sensory reward, and a bowl weight cannot tell the two apart.

A dog that finishes its ration has shown that the food was acceptable enough to eat. It has not shown that the dog liked it, and the gap between those two statements is the whole of this essay. There is a difference between eating a thing, accepting it, preferring it and taking pleasure in it. The phenomena overlap, and we have a single word, palatability, that we allow to cover all of them, and then we let the measurement of the easiest one stand as evidence for the rest.

An empty bowl proves that food was eaten. It does not prove that food was loved.

So perhaps we are not only under-measuring palatability. Perhaps we are over-interpreting intake. And it is worth asking the question plainly, because the whole industry answers it a hundred times a day without pausing on it: when a bowl comes back empty, what exactly have we been entitled to conclude?

Movement II

EATS TO LIVE

Here is the distinction the bowl cannot draw, and everything else follows from it. A pet must eat to live. But it may also eat because eating is rewarding, and sometimes an animal will take more than its immediate energy needs simply because the food is good. For analytical convenience these are often discussed as homeostatic feeding, the eating that answers a bodily need, and hedonic feeding, the eating that answers pleasure, although the underlying systems interact extensively rather than operating as two independent switches. Our difficulty is that the empty bowl records both at once and distinguishes neither. When we place a single food in front of a hungry animal, we are watching the homeostatic drive with the hedonic reward folded somewhere inside it, unseparated. The animal that clears the bowl has told us it was hungry enough to eat what was there. How much it wanted that particular food, as opposed to food, is a question the empty bowl leaves open.

The two-bowl test exists partly to close that gap, and it is a real improvement, because it introduces a choice. Put A beside B and let the animal decide, and now we can see how it distributed its eating, and which bowl it went to first. If A takes 70% and B takes 30%, we have good evidence that under those conditions the animals put more of their eating into A. We usually say A was preferred, and that is fair. But notice what the test did. It moved us from an absolute question, will you eat this, to a relational one, given these two, which will you eat more of. Preference now needs a comparator, and change the comparator and A's apparent quality changes with it. A food can lose 40:60 against an exceptional rival and be entirely acceptable. Another can win 60:40 against a poor one while neither food stirs much enthusiasm at all. A preference test has no winner without a loser, and it still does not tell us the thing we might most want to know, which is how much the animal actually valued the food it chose.

And hunger is not a constant sitting politely outside the experiment. It is inside it. The animal arrives in a physiological state, hungry or nearing satiety, carrying a feeding history and a set of learned associations and a temperament of its own, and its metabolism is a participant in our test. A sufficiently hungry animal has a reason to eat before the question of attractiveness even arises, and as it eats and hunger fades, the balance between drive and food-specific reward shifts under us. Which raises an uncomfortable possibility. The first grams and the last grams of a meal may not mean the same thing. Nor need the first meal and the twentieth.

Hunger asks the animal to eat. Palatability helps decide what it wants to eat.

We need, then, to be disciplined about words, because there is a hierarchy hidden inside the one we use most loosely. Need is the baseline, the homeostatic pressure to eat at all. Acceptance is the animal's willingness to eat this food rather than refuse it. Preference is how it divides its eating between alternatives when offered a choice. Wanting is how hard it will work to obtain one food over another. And liking, at the far end, is the hedonic question of pleasure that none of the others quite answers. Need, acceptance, preference, wanting, liking. The conventional bowl test observes the middle of that chain, acceptance and preference, and then quietly lets us infer rightward toward wanting and liking as though the steps were interchangeable. They are related. They are not synonyms, and the substitution of one for another is where a great deal of confidence has been manufactured. Later we will add a further construct the single meal cannot see at all, which is persistence, whether the animal still chooses the food after living with it, and that, it will turn out, is where the real disruption lies.

Movement III

THE DIET THE ANIMAL NEEDS MOST

If intake and liking come apart anywhere, they come apart most violently in the one place the stakes are highest, the sick animal and the diet meant to save it.

Consider the cat with chronic kidney disease. The therapeutic renal diet is one of the genuine achievements of veterinary nutrition. In the landmark trial, cats that ate one lived a median of 633 days against 264 for cats that did not, and that is not a marketing figure, it is survival. But the formulation problem here is unusually constrained. The nutrients most central to managing the disease, phosphorus above all, cannot simply be raised when they happen also to support sensory appeal, and the protein that carries much of a diet's phosphorus is moderated for the same clinical reason. Sodium is commonly kept low as well. None of this means palatability is impossible, and commercial renal diets are in fact engineered hard for acceptance. But it means the appeal has to be rebuilt inside a narrower nutritional envelope than an ordinary food enjoys, working around constraints an ordinary formulator never faces. The renal diet is, in large part by that necessity, among the harder foods in the category to make palatable. That is not an accident. It is the shape of the medicine.

Now feed it to the animal that needs it. The uraemic state that accompanies a failing kidney brings nausea and inappetence with it, and abnormal appetite is among the most commonly reported signs in these cats. So the very mechanism we have leaned on all along, the reliable hunger that empties a bowl and lets us read the emptiness as approval, is precisely the mechanism the disease takes away. The healthy dog at the fence may eat almost anything and hide the difference. The sick cat hides nothing, and will simply stop.

And the numbers from the clinic tell the story plainly. In that same survival trial, 21 of the 50 cats never reliably ate the diet at all, through limited intake or an owner unable to enforce the change. In a more recent survey of veterinarians, more than a third judged that the renal diet made up less than three-quarters of daily intake for most of their patients. On an intake sheet, a food that is mostly eaten reads as a formulation that mostly works. In the body of a cat quietly eating around it, it reads as a diet failing where it can least afford to, and a diet the animal refuses has, whatever the label promises, an efficacy it cannot deliver.

The healthy animal will eat to live and hide the difference. The sick animal hides nothing, and simply stops.

Intake is least trustworthy as a proxy for liking exactly where palatability matters most. Which leaves the clinician and the formulator holding an uncomfortable question. When the sick animal empties its bowl, or fails to, what have we measured, the food, or the disease?

We have been circling one half of the problem, the reading of the number, the way we let a gram of consumption stand for a measure of pleasure. Call that the interpretation problem, and it is real, and the sick cat shows how far it can go wrong. But over-reading the number is only the visible symptom, and beneath it sit two deeper faults that made the over-reading possible. We measure too little, because the test was built around what remains in the bowl rather than around the behaviour that emptied it. And we discard too much, because even the little we do capture is compressed, at the end, into a single figure. Three faults, then, stacked one on another. We measure too little, we discard too much, and we infer more than the measurement can support. The rest of this essay works down through those three layers, and then asks what we might build instead.

Movement IV

WHAT WE MEASURE

Begin with the measurement itself, because the first fault is built into the instrument. Return to the bowl. Before, 400 grams. After, 137. The animal consumed 263 grams, and what happened between the 400 and the 137 is very nearly everything we wanted to understand, and the protocol was designed to capture almost none of it. That is the quiet radicalism of the standard test. If palatability is a behavioural response that unfolds through time, why is the experiment built around what remains in the bowl at the end?

Think about what the animal actually did. How quickly it oriented to the food and approached it, whether it went straight to the bowl or hung back, how long it sniffed, how long between the first sniff and the first bite. Then, as it ate, how fast, in large bouts or small, accelerating or slowing. Whether it withdrew its head and came back, or switched bowls, and how often. Whether it lingered or bolted. When the meal ended, and, most telling of all, whether it came back. The two-bowl test enriches the picture by adding a choice, and first choice is a second genuine observation, but the architecture underneath stays the same. It is built around consumption as the endpoint. We kept the last number because a balance is cheap, robust and objective, while behaviour is messy, individuals differ, and scoring video by hand took forever. The field measured what it could measure well, and there is a quiet danger in that, because whenever the instrument defines the science, what is easy to measure slowly becomes what we believe the thing to be.

We built the experiment around what was left in the bowl, not around the animal that emptied it.

And what we left out has a shape, a timeline that a single endpoint erases. Aroma acts before the tongue arrives. Taste needs contact. Texture emerges during chewing. Fat contributes scent and mouthfeel and a chemistry that shifts as it warms. Hydrolysates release their amino acids and peptides once the food is sampled. Post-ingestive consequences arrive later still, some of them hours later. These cannot all be acting at the same instant, so no single final weight can tell us which of them mattered. Picture the sequence instead, detection to orientation to approach to first bite to sustained eating to return, and palatability stops looking like a number and starts looking like a process. Two foods can reach the same 65:35 ratio, one by seizing the nose and then losing the animal, the other by a slower approach and a longer, steadier meal. Those are not the same response. One captured the sniff. The other captured the meal. The bowl weight cannot tell them apart, and to the person trying to build the food, the difference is the entire job.

There is a whole dimension the endpoint cannot even reach, borrowed from a field that has studied it far longer. Behavioural science separates the motivation to obtain a reward from the pleasure of receiving it, wanting from liking, and shows the two can be pulled apart. We cannot ask a cat to rate its pleasure on a scale, and we should not pretend the human words map cleanly onto an animal. But the distinction reframes the whole enterprise. Instead of asking how much an animal ate when food was simply there, we can ask what it will do to get one food rather than another. Will it travel farther, wait longer, work harder, keep choosing that food as hunger fades and an easier option sits beside it. That question separates the need to eat from the wanting of this particular thing to eat, and it is far closer to what we meant by palatability all along. And notice what it does not give us. Even effort does not finally hand us liking. It hands us something different, and arguably richer, which is how strongly the animal is motivated to obtain the food, and the fact that our best new question still cannot reach pleasure directly is quietly fatal to the idea that there will ever be a single perfect palatability meter. The bowl never asked even this much, because the bowl was never designed to.

Movement V

WHAT WE DISCARD

Suppose, though, that the protocol never changed at all. Suppose we ran exactly the test we run today, the same bowls, the same 20 minutes, the same animals. There would still be a second fault, quite separate from the first, and in some ways more embarrassing, because it does not require any new experiment to see it. Even inside today's test, the animal generates far more information than we keep.

Imagine a two-bowl session that ends 65:35. Underneath that ratio, if anyone were recording it, is a sequence. At 3 seconds the animal orients to A. At 7 it sniffs A, at 11 it sniffs B, at 14 it returns to A, at 16 it takes the first bite, and eats without pause until it disengages near a minute, wanders to B, samples it briefly, then comes back to A and settles. A continuous weighing trace shows exactly how much went down in each bout. The final ratio, 65:35, is not the data. It is a single summary statistic sitting on top of a rich and largely discarded stream. We ran a behavioural film and kept one still frame from the end.

The intake ratio is not all the data. It is the one number we kept from a film we mostly threw away.

This is a different charge from the first, and worth keeping separate. The first fault is that the experiment was built too narrowly, around the endpoint. This one says that even within that narrow experiment, we collapse most of what we do observe. And this is the fault that technology is genuinely placed to fix, not by measuring more, but by keeping what the animal already shows us. A camera does not tire at the twentieth session. Computer vision can follow approach and orientation and the whole dance around the bowl. Load cells under the station turn two weighings into a continuous intake curve. Identity chips separate one animal from another automatically. Microphones can register patterns of crunching, chewing and pauses that the final weight never records. Researchers have even begun coding the faces of cats and dogs the way expression is read in pain and affective-state work, though it is early and no one should oversell a feline grimace. A word of precision matters here, because this territory is often described loosely. We are not reading an animal's mind or lighting up its brain. We are coding observable behaviour, the body and the face and the timing, and inferring a state from it, which is a far more modest and more honest claim. The behaviours the old test compressed, the sniff, the latency, the first bite, the bout structure, the return, are for the first time cheap to capture at scale.

But here is the discipline the whole essay turns on, and it is the most important sentence in it. More data is not more understanding. It would be the easiest thing in the world to bolt cameras and sensors and a machine-learning model onto the old test, generate a million measurements and learn nothing new. The question has to come first. What are we actually trying to know. Which behaviour carries information about it. Only then, which technology reads that behaviour reliably. Get that order wrong and we will have replaced an over-interpreted number with an over-engineered dashboard, and called it progress. Technology does not belong at the front of this story. It belongs in its proper place, between what we measure and what we understand, and never in the seat reserved for the animal.

Movement VI

BEYOND THE BOWL

So what would we build. Not, at first, a new machine, and not the abandonment of anything that works. The encouraging part is that the field has already begun to move, and much of what the next generation needs is here or arriving. A recent review of the field put it plainly: the one-bowl and two-bowl tests tell us how much is eaten but give little understanding of why the differences arise, and the newer work is turning toward behaviour, affective state and the analytical chemistry beneath. The upgrade comes in two stages, and the order matters.

The first stage keeps the established test exactly as it is, and instruments it. Keep the balance, keep the one bowl and the two bowls, so that decades of accumulated comparison are not thrown away, and simply stop discarding the rest of what the animal does in front of them. Add the continuous weighing, the vision, the individual identity, the timing of the feeding sequence. This is conservative, it is deployable now, and it costs the field none of its history. Its real value is not only the richer picture it gives. It is that it generates the evidence needed for the second stage, because only once we can see which behaviours actually carry information can we know what a better experiment should be built to capture.

The second stage is the genuine disruption. Having learned which parts of the feeding event mean something, redesign the experiment around the biology rather than around the convenience of the balance. Build protocols that deliberately separate attraction from acceptance, acceptance from preference, preference from motivation, and the single meal from the durable choice made after weeks of living with the food. That last is not a refinement. It is the whole commercial question, because the repeat purchase happens long after the panel has gone home, and a food can win a bright acute preference and lose the animal by the twentieth bowl.

This is also the point where artificial intelligence earns its place, and it is not the place it is usually given. The value is not a model that predicts a palatability score, which would only rebuild the old compression with more machinery. It is the fusion of streams that were never before brought together: the behaviour through time, the continuous intake, the identity of the animal, its previous exposures, and the measured chemistry and physics of the food. Bring those into one frame and we can stop asserting in advance what palatability is and let the data show us its structure. Perhaps there are foods that are high in attraction and poor in persistence, and others that are quiet at first and strong on return, and others that carry a hungry animal and collapse in a satiated one. Those categories should not be declared before the evidence exists. But an analysis that lets the dimensions emerge from the animal's own behaviour is a different enterprise from one that decides beforehand that everything must fold into a single word.

And here the old question itself begins to fail. We ask whether food A is more palatable than food B as though palatability were a single property, like moisture or protein, sitting in the food waiting to be measured. But suppose one food is thrilling at the nose, ordinary once eating begins and tiresome within a week, while another attracts less sharply, carries a meal beautifully and grows more preferred with familiarity. Which of them is more palatable. The honest answer is that the question has quietly folded several different biological phenomena into one word, and then asked a single number to carry all of them. The future is not a more accurate palatability score. It may be a palatability signature.

We have been asking which food is more palatable as though palatability were one thing. It may be several.

There is a second thing the old average hides, and it needs no new technology at all to see, only honesty about what a mean is. When a panel prefers A 60:40, that figure can mean most animals individually chose A in roughly that proportion, or it can mean half the animals strongly preferred A while half were indifferent or leaned the other way. The number on the report is identical while the underlying populations are entirely different. So the sharper question is not whether the panel preferred A. Did most animals prefer A, or did the average animal, which does not actually exist, prefer A? Once the identity chip and the camera let us follow the same animal across weeks, that question opens all the way up, and the interesting thing stops being that dogs preferred A 63:37, and becomes whether a given dog is consistent, whether one animal always responds to volatile attraction and another switches after 3 exposures, whether this cat approaches fast but ends meals early and that one refuses an unfamiliar food at first and comes to prefer it. The population mean washes all those trajectories together into a single ratio, and there is no average animal eating an average bowl beside the average owner buying the average bag. Longitudinal, individual phenotyping was economically impossible with a human scoring a panel by hand. It is not impossible now.

Tie those behaviours back to the chemistry and physics of the food, the volatiles associated with the approach, the lipid chemistry associated with sustained or declining engagement, the peptides that meet the tongue, the texture encountered during the chew, and the question stops being which palatant won and becomes why it won, when it won, and whether it will still win tomorrow. This is where the whole series converges. When a novel protein or a fermentation ingredient underperforms, the useful question is no longer simply whether the animal will eat it. It is where in the feeding sequence the unfamiliar ingredient does its damage. Does it dull the attraction, or is the attraction fine and the meal falls apart halfway through, or does the palatant rescue the first bite while the base formulation loses the animal by the twentieth. The Conversations on fats and plasma and hydrolysates were all, in the end, about single points along this sequence. A richer measurement is what lets us tell those points apart. There is a warning folded in, because a model trained on yesterday's ingredients may not understand tomorrow's proteins, and a fermentation product or a novel fat can sit outside the chemical space the model learned. The technology does not abolish the biology. It gives us another way to interrogate it, and the animal keeps the final vote.

Earlier I set out need, acceptance, preference, wanting and liking as a hierarchy, a ladder climbing from survival toward pleasure. Beyond the bowl, even that looks too neat. They behave less like rungs than like dimensions, interacting, sometimes moving together and sometimes pulling apart. An animal can want a food intensely and eat little of it because satiety has arrived, or accept a food for weeks without ever preferring it, or prefer one for its novelty and abandon it once the novelty is gone. Add attraction, meal engagement and persistence, and what we have been calling palatability stops looking like a score at all and starts looking like a signature. The essay began by finding a hierarchy hidden inside one loose word. It ends by finding that even the hierarchy was too simple.

I will not, in this essay, walk through how those signals are assembled into a working answer, because that assembly is the work itself, the point where the science stops being a public conversation and becomes someone's craft. The lighthouse can be described without handing over the map. But the thing the whole essay has been driving toward is simpler than any method. These signals are not unmeasurable. They are merely unmeasured by the standard test. The animal has been producing them all along, at every session, in plain view, and they disappeared not because they were invisible but because we were weighing the bowl.

None of which makes the bowl primitive. Sometimes the simplest measurement is the right one, and if I were launching a food tomorrow I would still want to know, plainly, whether animals eat it and whether they prefer it to what it replaces. But scientific maturity is knowing what a measurement cannot say. Intake is real, preference is real, first choice is real, and the danger begins only when we quietly enlarge them into something bigger than the behaviour we watched. The bones disappeared over the fence. The test food disappeared in the panel room. Both left the same evidence, an empty vessel and an animal that ate what was there, and the biology that emptied them was not necessarily the same. That difference, invisible on the balance, is the whole of it. A pet eats, in part, because life requires eating, and folded inside that necessity is everything else, attraction and choice and reward and persistence and learning, and something that in plain language we would call liking. For decades most of it vanished between the first weighing and the second. It did not vanish for the animal. It vanished for us.

So the question I would leave open is not whether the bowl was wrong. It was not. It is whether we are still willing, now that we can see so much more of the meal, to keep asking the animal only the one question the balance was built to answer. I do not think we should be. But that is a decision the industry has to make with its eyes open, and it has not yet, to my knowledge, even been put as a question.

We measure too little, we discard too much, and we infer more than the measurement can support.

The empty bowl has told us a great deal. It is time we found out what happened beyond it.

References

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About the Author

Tuesday, 1 September 2026

Protein Hydrolysate Palatability in Pet Food: Where to Stop the Cut

Where to Stop, The Friday Conversation No. 7. From papaya leaf to reactor, the protein hydrolysis continuum from intact protein to free amino acids.

On protein hydrolysates in petfood: when breaking protein makes food more palatable, when it does not, and why the animal decides where to stop.

In parts of this world, when the meat is tough, you wrap it in the leaf of the papaya tree and leave it a while before it meets the fire. In others you bury it, or hang it in the cold until the flesh gives up its stiffness on its own. My grandmother's generation did not call any of this chemistry. They called it good sense, and they were right, and they were also, without a word of the vocabulary, running a controlled enzymatic reaction on a kitchen table.

The papaya leaf carries papain. The pineapple carries bromelain, the fig its ficin, and the meat, left to itself in the cold, carries its own quiet proteases that go on working long after the animal has stopped. All of them do the same thing. They cut the long protein chains of muscle into shorter pieces, and the shorter pieces eat more tenderly, release more savour, and give the tongue more to find. Tenderisation is not softening in the way a soak in water softens. It is scission. It is the protein being taken apart, a little, on purpose, for the pleasure of the eater. And humans have been doing it, deliberately and with real skill, for far longer than they have had a name for the enzyme that does the work.

There is an older cousin to this, and the line between them is thinner than it looks. Long before refrigeration, communities learned to let meat and fish sit under the work of time and microbes, and to prize what came out: the deep, resonant flavour of a cured ham, a fermented fish, a sauce drawn from anchovies left to their own slow dissolution. We call that fermentation, and it is more than enzymes, microbes and time and salt all playing their parts. But enzymes are unmistakably in it, because much of what fermentation does to flavour, it does by proteolysis, by cutting protein into the fragments and free amino acids the tongue reads as savoury. Fermentation for flavour and tenderisation for tenderness are, at the level of the protein, close kin. Both are the controlled disassembly of protein for a sensory reward.

So the question this essay begins with is not a modern one at all. It is the one the grandmother answered with a papaya leaf, asked again with instruments: what happens, exactly, when you take a protein apart, and why has every food culture that ever lived gone to such trouble to do it?

Movement I

FROM THE LEAF TO THE REACTOR

The difference between the papaya leaf and the modern reactor is not the chemistry. It is the control.

When you wrap a tough cut in a papaya leaf, you get whatever the leaf happens to give you, for as long as you happen to leave it, at whatever temperature the kitchen happens to be. The enzyme works where it lands and stops when the heat of the fire finally destroys it, and the result is a better piece of meat and a great deal you never measured. It is real skill, but it is skill of the hand and the eye, passed down and adjusted by taste. What the last century added was not a new reaction. It was the dial. Choose the enzyme, and you choose which bonds along the chain get cut. Choose the temperature and the acidity and the time, and you choose how far the cutting goes. Stop it when you decide to stop it, and you fix the product exactly where you want it. The grandmother cut her protein by feel. The industry learned to cut it to a number.

The grandmother cut her protein by feel. The industry learned to cut it to a number.

That number has a name, the degree of hydrolysis, and it is simply the proportion of the protein's bonds that have been cut, from a whisper of cleavage to extensive fragmentation into small peptides and free amino acids. Everything that matters in this essay hangs on where along that range you choose to stop, because the protein is a different material at every point, and it behaves differently in the bowl and in the gut depending on where you left it.

This is not a marginal craft. Enzymatic hydrolysis is now a major industrial route to these ingredients, and the trade has grown into a substantial one precisely because controlled cutting turns out to be useful in ways the papaya leaf only hinted at. The proteins that go into it are drawn from wherever good protein can be had: whey and casein from milk, collagen from hide and bone, muscle and organ from slaughter, poultry, and a large and growing share from fish. And increasingly from plants, too, soy above all, along with pea and rice and wheat gluten, which matter more to this story than their share of the market suggests. Plant proteins are where hydrolysis has long been most notorious for the bitterness it can bring, and soy hydrolysate is the substrate on which a great deal of what we know about bitter peptides was first learned. In pet food the pull is strongest at the premium and therapeutic end, where hydrolysates are prized for two properties above all, and it is worth being precise about what those two properties are, because the rest of this essay is about the fact that they do not always come together.

The first is digestibility. A protein already cut into peptides has undergone part of the proteolysis the animal would otherwise perform for itself, and in some formulations and physiological circumstances that can alter the rate and pattern with which its nitrogen becomes available, which matters most for the young, the old, the recovering, and the compromised gut. The second is that extensive hydrolysis can reduce antigenicity, breaking the protein into fragments less able to be recognised by the immune system as the shape it once reacted to, which is why extensively hydrolysed proteins are reached for in the elimination and management diets of the allergic animal. These are real reasons for hydrolysing a protein, and they are why a formulator reaches for the tool. But neither of them tells us whether the resulting food will be eaten. Both are reasons of the gut, not the mouth, and a diet the animal refuses has a nutritional value of zero no matter how digestible or how hypoallergenic it is on paper. So the question this essay is really about is not what hydrolysis does to a protein. It is what hydrolysis does to a protein's chances at the bowl. And there the story stops being a list of benefits and becomes something far less obedient.

Movement II

THE SAME CUT

Here is the thing the papaya leaf never had to reckon with, because it never cut very far. The same scission that delivers the digestibility and the hypoallergenicity also does two other things, in the same stroke, that no one asked it to do. It is not that hydrolysis has a benefit and, separately, a side effect. It is that the cut is single and its consequences are plural. You cannot take the protein apart for one reason and leave the other reasons uninvited.

Consider what the cut does to taste, which turns out to be two opposing things at once. Cleaving protein releases free amino acids and small peptides that profoundly change flavour, and to a human tongue some of them carry a savoury character, the deep meaty resonance that has drawn every long-cooked stew and every aged cheese and every drop of fish sauce toward the same chemistry. But here the caution this whole series keeps returning to becomes almost the point. The cat does not read that chemistry as we do. Its savoury sense, the work of the palatability scientists tells us, is not built around glutamate the way ours is; it appears to lean more on nucleotides, with amino acids playing a supporting part, and the glutamate and aspartate that anchor the human idea of umami do not map cleanly onto how a cat responds at all. Kokumi, the mouth-filling roundness that is less a taste than an enrichment of the others, appears to be functional in the cat too, one more channel through which a broken-down protein might reach the animal.

So when hydrolysis unlocks a savour that sat mute inside the intact chain, we should be careful whose savour we mean, and honest that we do not fully know which of these channels a given cut is feeding, and which it is starving. We can release the molecules confident that they are appetising and be describing our own tongue rather than the animal's. But whatever the cat makes of that half, the very same cutting, carried further or aimed differently, can also do the opposite. It exposes the hydrophobic amino acids that had been folded safely inside the protein, and hydrophobicity is strongly associated with bitterness, though it is not the whole story. Hydrophobicity is a useful first clue to where the bitterness may reside, never a complete explanation of it: the more hydrophobic peptides tend to be both the more bitter ones and the ones that behave differently when you try to separate a hydrolysate by that property.

Some years ago I worked on exactly this, removing the bitterness and the salt from a whey protein hydrolysate at the same time by letting the bitter, hydrophobic peptides interact selectively with an adsorbent and lifting them out on that interaction. It works because bitterness is not scattered randomly through a hydrolysate; it rides on a physical characteristic you can act on. But knowing that bitterness and hydrophobicity travel together is a long way from knowing, for a given protein and a given purpose, where the balance tips. And the relationship between how far you cut and how bitter the result is turns out to be more interesting than a straight line. Bitterness depends on the substrate, the sequence, the size of the peptides and the specificity of the enzyme, and as the cutting proceeds it can rise as bitter hydrophobic peptides are liberated, peak, and even fall again as further cutting breaks those same peptides down. Every cut changes the peptide population, and the bitterness rides that changing population up and down rather than simply climbing. There is no monotonic dial you can simply turn less of. There is a moving target.

The cat makes this harder still, and in a way that ought to keep us humble. An obligate carnivore might be expected to have surrendered much of the bitter-detection apparatus that other animals use to avoid the toxins of plants. It did not; the domestic cat carries a substantial repertoire of bitter receptors that respond, in the laboratory, to bitter compounds. But a receptor firing in a dish is not the same as an animal tasting bitterness, still less disliking it, and the older work on how cats actually respond to bitter stimuli is genuinely murky, some of it pointing to responses that lack the clean specificity we would want before saying with any confidence what the cat perceives. So the honest position is a question rather than a claim. We know the cat kept the machinery, and we know a little of what it does with some of it: cats will reject quinine, so the apparatus is not idle. But quinine is a plant alkaloid, and the bitterness a hydrolysate carries is a different chemistry, a matter of peptides and exposed residues, and how the cat meets that is far less clear. We call these bitter receptors, but they earn the name only by resemblance to ours; the label is borrowed from the one species that can say what it tastes. When the cat's version fires, we do not actually know that the animal experiences bitterness as we would recognise it. The researchers who first characterised these receptors said as much, that the cat may detect a narrower, or simply a different, range of bitter things than we do, and that its bitter world has scarcely been studied. It might register something we have no word for, and the cat cannot tell us, because the one instrument that could settle the matter, its own report, is the one a cat does not have.

So the questions stack. Does the bitterness a cut liberates register at all in the cat; if it does, does it register as bitterness or as some other thing we cannot name; and if as bitterness, does a carnivore that meets such compounds in prey rather than in poison read them as an aversion to be masked, or make very little of them? I do not think anyone can answer that from a receptor, and until someone answers it some other way, a great deal of what we say about bitter hydrolysates and cats is really being said about our own tongues. The savour and the bitterness are not two ingredients you can order separately. They are two faces of the one act of cutting, and where you stop decides which face is showing.

The same cut that unlocks the savour exposes the bitter. You do not get to invite one and refuse the other.

Now consider what the cut does to structure, and here the essay meets its two predecessors. An intact protein can build things. It can be heat-set into a gel, woven into a network that holds water and fat and gives a chunk its bite, which is the entire subject of the two conversations that came before this one. Cut that protein into peptides and you take that ability away. A hydrolysed protein has been relieved of the very architecture that let it bind, because the long chains that entangled and cross-linked and held are now short pieces that cannot. So the tool that improves digestion dismantles structure in the same motion. The gain in digestibility is paid for in structure, and the loss is not incidental. It is the direct arithmetic of cutting a long thing into short things.

This is why there is no single best form of a protein, only a best form for a purpose, and it is worth laying the spectrum out honestly. At one end sits the intact protein: full structure, its savour locked up, and asking the animal's gut to do the work of breaking it down. At the far end sits the pool of free amino acids: no peptide bonds left for a protease to cleave, no peptide structure left to build a network with, and a sensory character that can be powerful without necessarily being attractive. And in the enormous middle sits the hydrolysate, wherever you chose to stop it, carrying some of each virtue and some of each cost. But it would be too tidy to call this a single spectrum with the good things at one end and the bad at the other. Every movement of the dial changes several properties at once, and they do not move in step, and they do not reach their best points together. Digestibility, structure, savour, bitterness: each follows its own curve as the cutting proceeds, rising and falling on its own schedule, and the peaks and troughs do not line up. The dial does not have a setting that is best at everything, and not merely because the properties compete along a line, but because they are several different response curves laid over one another, and no single point sits at the top of all of them.

Movement III

WHEN A HYDROLYSATE IS NOT A PALATANT

The word hydrolysate describes what we did to the protein. The word palatant describes what the animal thought of the result. They are not the same word, and they do not always describe the same thing, and the entire difficulty of this trade lives in the gap between them.

A hydrolysate can be, by every measure a laboratory can put to it, an excellent thing. Its nitrogen readily available, its antigenicity low, its solubility complete, its amino acid profile answering the animal's needs point for point. And it can still be met at the bowl with refusal, because none of those virtues is the same as being wanted. The cut that made it so digestible may have carried the bitterness up onto its peak. The peptides that make it dissolve so cleanly may be exactly the ones the cat's kept receptors object to. A protein can be hydrolysed perfectly for nutrition and badly for palatability, and the two failures are invisible to each other. The nutritionist's instruments will report a triumph while the animal walks away.

Hydrolysate describes what we did to the protein. Palatant describes what the animal thought of the result.

Collagen offers a particularly visible demonstration of what progressive dismantling can do, because it has been walked down that road in front of us for a century. In its native state it is highly ordered and structurally formidable, with real technological and nutritional consequences of its own. Disrupt that ordered triple helix through denaturation and partial hydrolysis into gelatine, and its behaviour changes dramatically: it becomes dispersible and can set a thermoreversible gel, a reminder in passing that the cut can be made by chemistry as readily as by the papaya leaf's biology. Hydrolyse it further into smaller collagen peptides and that gel-forming capacity largely disappears, leaving a soluble, available fragment that builds nothing. One parent protein, progressively dismantled into materials with profoundly different functions, and not one point along that road that is best at everything. Where you would stop, for collagen or for any protein, depends entirely on what you were trying to make, and whether the animal agrees is a separate question the road cannot answer.

None of this is waste rescued from a bin. The tougher streams a slaughter leaves, the connective tissue and the harder material, are already valorised into the rendered meals and fats that are real ingredients in their own right, and hydrolysis is simply a further rung on that ladder, a way of taking something already useful and giving it a different functionality, perhaps more soluble, perhaps more digestible, and potentially more useful within a palatability system. But none of those transformations guarantees that the animal will want it. You can climb every rung of nutrition and functionality and still arrive at a material the animal declines, because willingness is not a rung on that ladder at all. It is the judgement waiting at the top, and it belongs to the eater.

Which leaves a question worth sitting with, if you make or buy these ingredients. Before the animal has told you, how would you know whether the excellent hydrolysate in front of you is a good palatant? What, exactly, would you measure? We have instruments for every rung of the ladder and none for the judgement at the top, and I am not sure the industry has been honest with itself about how much of what it calls palatability prediction is really just the hope that the two will coincide.

Movement IV

WHERE TO STOP

So the whole art, in the end, comes down to a decision the papaya leaf never had to make consciously: where to stop the cut.

Stop too early and the protein may remain little changed, much of its original structure intact, its immunoreactive epitopes potentially preserved, and whatever sensory potential the cutting might have released still largely locked away. Cut too far and you have a pool of free amino acids that the gut absorbs in an instant, the structure gone entirely and the savour at risk of tipping over into a rawness the animal may or may not accept. Somewhere between those, for any given protein and any given purpose, there is a place to stop that gives the animal enough of what it needs and spares it enough of what it will not tolerate. That place is different for a hypoallergenic diet than for a digestibility aid, different for a fish protein than for a collagen, different for a cat than for a dog. It is not one setting. It is a judgement made freshly each time, against the specific material and the specific animal and the specific job the ingredient has to do.

I am not going to tell you, in this essay, how that judgement is made. Partly because it is the working life of people like me and not a thing to be given away in a Friday paragraph, but also because the answer is not a universal number. It belongs to the substrate, the process, the purpose, and, ultimately, the species doing the eating. It is the accumulated feel for a tool that the industry has spent decades learning, the modern inheritor of exactly the skill the grandmother had with her leaf, only now aimed with instruments and held to a number. What can be said plainly is what the decision is between, and this whole conversation has been an attempt to say it: between digestion and structure, between savour and bitterness, between what the gut will take and what the mouth will accept, all of them moving at once, all of them tied to the single fact of the cut.

There is no setting that is best at everything. There is only the setting that is best for this.

And here is where the title of this conversation finally asks its real question. Where to stop the cut is not, in the end, a question the laboratory can close. You can measure the degree of hydrolysis. You can measure the size of the peptides and the quantity of free amino acids, the solubility, the digestibility, and with enough patience even the bitterness. There are instruments now, electronic tongues and noses and the models built on top of them, that read these properties and predict, sometimes rather well, how a food is likely to be received. But prediction is not preference, and correlation is not consent. Every one of those readings is a number, and not one of those numbers is the animal's yes. The best of them forecast the verdict. None of them is the verdict. Which ought to unsettle us more than it does, because we specify these ingredients to numbers all the same. When we write a hydrolysate to a target, are we describing what the animal will accept, or only what the quality sheet can check? The two are not the same, and the gap between them is where a great many refused bowls have quietly lived.

The laboratory measures hydrolysis. The animal measures palatability.

The grandmother knew when the meat was ready. She knew it the way you know these things, by the eating. We have better tools than she had, and a great many more numbers, but at the very end we are still waiting on the same verdict she was, and it is not a verdict any instrument can return. We can say, with all the precision in the world, exactly how far we cut the protein. Only the animal can tell us whether we stopped in the right place.

Which means the question was never really only where to stop the cut. It was how to learn to ask the animal sooner, before the batch is made, before the diet is formulated, and before the refusal comes back from the bowl too late to do anything about it. I do not think we have answered that question yet. I am not sure we have been asking it in the right language. And that, more than any degree of hydrolysis, is the conversation I would like us to be having.

The bowl, as always, decides.

References

1. Cheison, S.C., Wang, Z. & Xu, S.-Y. (2007). Use of macroporous adsorption resin for simultaneous desalting and debittering of whey protein hydrolysates. International Journal of Food Science & Technology 42(10):1228-1239. doi:10.1111/j.1365-2621.2006.01461.x

2. Cheison, S.C. & Kulozik, U. (2017). Impact of the environmental conditions and substrate pre-treatment on whey protein hydrolysis: A review. Critical Reviews in Food Science and Nutrition 57(2):418-453. doi:10.1080/10408398.2014.959115

3. Liu, B., Li, N., Chen, F., Zhang, J., Sun, X., Xu, L. & Fang, F. (2022). Review on the release mechanism and debittering technology of bitter peptides from protein hydrolysates. Comprehensive Reviews in Food Science and Food Safety 21(6):5153-5170. doi:10.1111/1541-4337.13050

4. Fu, Y., Chen, J., Bak, K.H. & Lametsch, R. (2019). Valorisation of protein hydrolysates from animal by-products: perspectives on bitter taste and debittering methods. International Journal of Food Science & Technology 54(4):978-986. doi:10.1111/ijfs.14037

5. McGrane, S.J., Gibbs, M., Hernangomez de Alvaro, C., Dunlop, N., Winnig, M., Klebansky, B. & Waller, D. (2023). Umami taste perception and preferences of the domestic cat (Felis catus), an obligate carnivore. Chemical Senses 48:bjad026. doi:10.1093/chemse/bjad026

6. Laffitte, A., Gibbs, M., Hernangomez de Alvaro, C., Addison, J., Lonsdale, Z.N., Giribaldi, M.G., Rossignoli, A., Vennegeerts, T., Winnig, M., Klebansky, B., Skiles, J., Logan, D.W. & McGrane, S.J. (2021). Kokumi taste perception is functional in a model carnivore, the domestic cat (Felis catus). Scientific Reports 11:10527. doi:10.1038/s41598-021-89558-w

7. Sandau, M.M., Goodman, J.R., Thomas, A., Rucker, J.B. & Rawson, N.E. (2015). A functional comparison of the domestic cat bitter receptors Tas2r38 and Tas2r43 with their human orthologs. BMC Neuroscience 16:33. doi:10.1186/s12868-015-0170-6

8. Lei, W., Ravoninjohary, A., Li, X., Margolskee, R.F., Reed, D.R., Beauchamp, G.K. & Jiang, P. (2015). Functional analyses of bitter taste receptors in domestic cats (Felis catus). PLoS ONE 10(10):e0139670. doi:10.1371/journal.pone.0139670

9. Cho, M.J., Unklesbay, N., Hsieh, F.-H. & Clarke, A.D. (2004). Hydrophobicity of bitter peptides from soy protein hydrolysates. Journal of Agricultural and Food Chemistry 52(19):5895-5901. doi:10.1021/jf0495035

10. Schrieber, R. & Gareis, H. (2007). Gelatine Handbook: Theory and Industrial Practice. Wiley-VCH, Weinheim.

About the Author

Dr. rer. nat. habil. Dr. Seronei Chelulei Cheison is the founder and Chief Executive Officer of Sinonin Biotech GmbH, where he works with petfood companies on palatant sourcing strategies and the innovation of palatability enhancers. A trained food enzymologist, he led alternative protein and palatant development at Mars Petcare before founding Sinonin, and his research on enzymatic protein hydrolysis spans two decades, a doctorate from Jiangnan University, and a habilitation from the Technical University of Munich.