Dr.habil. Dr. Seronei arap Chelulei Cheison

Thursday, 24 September 2026

Petfood palatability in veterinary diets: what the patient will eat

The First Mouthful, The Friday Conversation No. 10. A nutritionally complete veterinary diet in a bowl and a cat walking away, the challenge of feeding the animal that needs the food but may not want it.

The First Mouthful. The palatability challenge in veterinary diets: when what the animal needs to eat and what the animal wants to eat are not quite the same thing.

Somewhere today a nutritionist finishes a formula for a sick cat. Every number on the sheet is right. The phosphorus is where the failing kidney needs it, the protein carefully judged, the mineral and acid-base balance attended to, the energy and essential nutrients accounted for. It is, on paper, a small triumph of veterinary nutrition, a diet that could genuinely slow a disease and lengthen a life. And then it is put down in front of the cat, and the cat looks at it, and walks away.

Nothing on the sheet was wrong. A veterinary diet can be perfectly formulated for the disease and badly formulated for the patient, and the two are not the same achievement.

This is the quiet difficulty at the centre of therapeutic nutrition, and it is a different difficulty from the one an ordinary pet food faces. An everyday food is designed to be wanted, and if the animal wants it, the job is largely done. A veterinary diet is designed to be needed, and being needed is not the same as being wanted. The clinical target and the animal's appetite are set by different authorities that do not consult each other. The kidney has its requirements. The nose has its own. And a diet does not become therapeutic when the nutritionist finishes the formula. It becomes therapeutic when the patient eats it.

So the question this essay begins with is one the analytical sheet cannot answer, and it is worth asking plainly, because so much sophistication rides on it. When what an animal needs to eat and what it wants to eat are not quite the same thing, which of the two decides whether the medicine works?

Movement I

THE COLOURS THE DISEASE REMOVED

To see why this is hard, start with the question each kind of formulator is actually asking, because they are not asking the same one.

The developer of an ordinary pet food asks, broadly, a question of addition. What can I bring forward, or turn up, to make this food more attractive? That formulator is far from unconstrained, since nutrition, safety, processing, cost and regulation all bind the work, but within those bounds there is considerable freedom to chase the palate. The developer of a veterinary diet asks the same question of attraction inside a much narrower clinical corridor. What can I use without compromising what this food is supposed to do? The clinical target comes first and is not negotiable, and the palate has to be satisfied in whatever room is left over. One formulator works on a wide canvas. The other works on a canvas where the disease has already painted, in fixed colours that cannot be moved, and has taken several of the best colours away.

Consider what the constraint actually means. A phosphorus ceiling for a failing kidney is not a preference to be balanced against palatability; it is a wall. A hydrolysed protein selected for an elimination diet cannot simply be swapped for a familiar intact one to improve acceptance, because doing so may defeat the diagnostic or therapeutic purpose the diet exists to serve. The mineral balance a urinary diet must hit is a chemistry the formulation has to deliver, not an aspiration. In each case a lever that an ordinary formulator would reach for without a second thought has been bolted to the floor, and often it is precisely the lever that would most have helped the food be eaten. The disease does not just set the nutritional brief. It confiscates the tools.

The ordinary formulator asks what to add. The veterinary formulator asks what is left.

An earlier Conversation looked hard at the sick animal from the side of measurement, and found that intake is the least trustworthy thing we measure in exactly this patient, because the reliable hunger that lets us read an empty bowl as approval is the first thing many diseases take away. Grant all of that. This essay stands on the other side of the same problem and asks a different question. Not how we misread the sick animal at the bowl, but how we formulate for it at the bench, knowing the appetite we are formulating for may already be compromised before the food is ever set down. The measurement problem and the formulation problem are two faces of one difficulty, and this is the second face.

Which is why the challenge cannot be met by the reflex the phrase invites. Told that veterinary diets are hard to make palatable, everyone reaches for the same answer, that we should simply make them more palatable, work harder at the acceptance, push the appeal. That is not wrong, but it is not sufficient, and it may not always even be the right aim. So before we ask how to make a therapeutic diet more palatable, a prior question is worth sitting with. What, exactly, has each disease forbidden, and how differently does each one break the quiet agreement between what an animal needs and what it wants?

Movement II

FOUR WAYS TO BREAK THE AGREEMENT

Between what an animal needs and what it wants there is, most of the time, a quiet agreement. Fresh meat is both nourishing and delicious; the food that keeps the animal alive is the food it enjoys, and evolution arranged the overlap on purpose. Therapeutic diets are the places where that agreement breaks, and it is worth seeing that it breaks in four quite different ways, because the difference is the whole subtlety.

The renal diet breaks it by subtraction. To slow a failing kidney the formulation restricts phosphorus, the protein quantity and quality have to be judged carefully, and the rest of the formulation is built around maintaining adequate nutrition inside those limits. Each of those judgements is a clinical necessity, and several of them remove or constrain something the palate was using. The diet is asked to be appealing with several of appeal's usual instruments taken out of its hands, and it is asked to be so for an animal whose illness has often dulled its appetite before the bowl is even filled. Need and want here are not in conflict so much as starved of common ground.

The elimination diet breaks the agreement more sharply, almost cruelly. Its whole purpose is to feed a protein the immune system cannot recognise, either one the animal has never met or one hydrolysed into fragments less likely to retain the antigenic structures that provoke the reaction, so that the source of an allergy can be found or managed. Now consider the ordinary formulator's instinct, which is to reach for a familiar, savoury animal protein and the flavour systems built around it. Many of those the elimination diet simply cannot admit, because the familiar ingredient is the very kind of thing the trial exists to exclude. The most convenient tools of acceptance are ruled out by the diagnosis itself. And hydrolysis, which solves the immunological problem, does so only by creating a new sensory one, since the same cutting that hides the protein from the immune system can, as an earlier Conversation followed in detail, expose a bitterness the tongue reads all too well. The diet has to win acceptance with much of the usual toolkit closed to it, and with a process that can work against the palate even as it serves the diagnosis.

The most convenient tools of acceptance are the ones the diagnosis rules out.

The urinary diet breaks it in yet another way, by making the animal's own consumption the delivery mechanism. The point of the diet is to alter the urinary environment, through mineral composition, urine concentration and, where appropriate, urine pH, so that conditions become less favourable to the particular crystal or stone at issue. And that altered environment only reaches the bladder through what the animal actually eats and drinks. A urinary formula that is perfect on the specification sheet and left in the bowl protects nothing. Here need and want are welded together in an uncomfortable way, because the therapeutic effect is not delivered by the formula at all. It is delivered by the eating.

And then there is the obesity diet, which breaks the agreement most interestingly of all, by reversing the goal. Every diet so far wanted the animal to eat and struggled to make that happen. The weight-management diet needs the animal to be nourished and satisfied on fewer calories, and its whole purpose is undone if the result is simply that the animal eats more. The food still has to be palatable enough to be accepted, because a refused diet helps no one. But acceptance is not the same as maximum consumption, and here, for once, the therapeutic objective is plainly not to make the animal eat as much as it possibly can. Which forces the question the whole essay has been circling toward. If one therapeutic diet succeeds by being eaten more and another succeeds by being eaten less, can the aim of veterinary palatability really be, as we so easily assume, simply to make the animal eat as much as possible?

Movement III

THE FIRST MOUTHFUL

There is one more thing the specification sheet cannot hold, and it may be the most important of all. A diet is not eaten in the abstract. It is eaten by a particular animal, at a particular moment, and the moment matters as much as the food.

We are tempted to speak of a food as though palatability were a fixed property of it, as though a diet were simply palatable or unpalatable the way it is high or low in phosphorus. But an animal does not meet a food the way an instrument meets a sample. It arrives carrying a physiological state, a history of what it has eaten and how that turned out, and a memory, and for the therapeutic patient every one of those is likely to be working against the meal. The food designed for the sick animal very often first meets that animal on one of the worst eating days of its life, at the moment of diagnosis, when it feels least like eating, and is asked at that exact moment to accept something unfamiliar. This is why refusal at the bowl is not one problem but several wearing the same face. Sometimes the patient is rejecting the food itself. Sometimes it is rejecting the memory of what happened the last time it ate, a nausea the food has been unluckily paired with. And sometimes it is not rejecting the food at all, but is simply too unwell to want to eat anything. Those are three different problems, and clinical guidance is right to insist that the medical causes of a poor appetite be addressed before the food is blamed for it. Palatability, seen this way, is not a number stamped on the food. It is what happens in the meeting between a food in a particular state and an animal in a particular state, and the sick animal brings the harder half of that meeting.

Palatability does not reside in the food alone. It happens between this food and this animal, on this day.

So return, at the end, to the cat we began with, and to the perfect formula it walked away from. Notice what has and has not changed. The formulation has not changed. The analytical sheet, with every number in its place, has not changed. The disease has not changed. All the nutritional sophistication that could slow that cat's illness is still sitting in the bowl exactly as designed. Only one thing stands between that sophistication and the patient it was built for, and it is not a molecule, and it is not on any sheet. It is whether the cat eats.

We have spent a great deal of veterinary nutrition, and a great deal of real ingenuity, on the first half of a sentence, asking what the sick animal should eat. It may be time to give equal seriousness to the second half, which is quieter and less flattering to our chemistry, and asks only whether the sick animal will eat it. The first half is a question of knowledge. The second is a question of acceptance, and acceptance is where the knowledge either reaches the patient or fails to.

Because for the animal in front of the bowl, the old opposition dissolves. Eat to live and live to eat were never really opposites here. The eating is not a reward that follows the therapy or a pleasure separate from it. The eating is the therapy's first and non-negotiable step, the point at which everything the formulation knows either enters the animal or does not. A therapeutic diet left in the bowl cannot deliver the therapy it contains.

The treatment begins with the first mouthful.

References

1. Elliott, J., Rawlings, J.M., Markwell, P.J. & Barber, P.J. (2000). Survival of cats with naturally occurring chronic renal failure: effect of dietary management. Journal of Small Animal Practice 41(6):235-242. doi:10.1111/j.1748-5827.2000.tb03932.x

2. Magalhães, T.R., Corbee, R.J., Queiroga, F.L. & Lourenço, A.L. (2026). Acceptance and preference of a commercial dry renal diet in healthy cats: an in-home proof-of-concept trial. Journal of Animal Physiology and Animal Nutrition. doi:10.1111/jpn.70043

3. Ilias, N., Zaki, A.H.H., Awang Junaidi, A.H., Lau, S.F., Saufi, I. & Ajat, M. (2022). Palatability assessment of prescribed diets on domestic shorthair cats. Veterinary World 15(3):640-646. doi:10.14202/vetworld.2022.640-646

4. Magalhães, T.R., Lourenço, A.L., Corbee, R.J. & Queiroga, F.L. (2023). Clinical management of feline chronic kidney disease in Portugal: a questionnaire-based study. Journal of Feline Medicine and Surgery 25(11):1098612X231206125. doi:10.1177/1098612X231206125

5. Weber, M., Bissot, T., Servet, E., Sergheraert, R., Biourge, V. & German, A.J. (2007). A high-protein, high-fiber diet designed for weight loss improves satiety in dogs. Journal of Veterinary Internal Medicine 21(6):1203-1208. doi:10.1111/j.1939-1676.2007.tb01939.x

6. Berridge, K.C. & Robinson, T.E. (2016). Liking, wanting, and the incentive-sensitization theory of addiction. American Psychologist 71(8):670-679. doi:10.1037/amp0000059

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, 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

1. 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

2. Tobie, C., Péron, F. & Larose, C. (2015). Assessing food preferences in dogs and cats: a review of the current methods. Animals 5(1):126-137. doi:10.3390/ani5010126

3. Calderón, L.A., Berendsen, B., Verbeek, E. & others (2024). Measuring palatability of pet food products: sensory components, evaluations, challenges, and opportunities. Journal of Food Science 89(9):5359-5382. doi:10.1111/1750-3841.17511

4. Elliott, J., Rawlings, J.M., Markwell, P.J. & Barber, P.J. (2000). Survival of cats with naturally occurring chronic renal failure: effect of dietary management. Journal of Small Animal Practice 41(6):235-242. doi:10.1111/j.1748-5827.2000.tb03932.x

5. Magalhães, T.R., Lourenço, A.L., Corbee, R.J. & Queiroga, F.L. (2023). Clinical management of feline chronic kidney disease in Portugal: a questionnaire-based study. Journal of Feline Medicine and Surgery 25(11):1098612X231206125. doi:10.1177/1098612X231206125

6. Berridge, K.C. & Robinson, T.E. (2016). Liking, wanting, and the incentive-sensitization theory of addiction. American Psychologist 71(8):670-679. doi:10.1037/amp0000059

About the Author

Wednesday, 16 September 2026

The Galaxy of Generalisation: A Reply to Matt Lawton

Nairobi did not steal the 2029 World Championships from London. London lost a vote, and a section of the British press has chosen to lose its composure.

By Dr. rer. nat. habil. Dr. Seronei Chelulei Cheison

Matt Lawton, Chief Sports Correspondent of The Times, reacted to Nairobi's award of the 2029 World Athletics Championships by calling it an "incredible decision", his first stated objection being that it meant "three consecutive champs away from Europe". When challenged, he added: "Massive doping problem in Kenya." He has now expanded that objection into a column headlined "It's wrong London lost out on World Championships to nation tainted by doping", arguing that it is "far too soon" to entrust Nairobi with the championships. Let us take the argument seriously, because it deserves a serious answer.

The complaint that indicts itself

Mr Lawton's first grievance, stated in his own words, was that Nairobi 2029 means three consecutive championships held outside Europe: Tokyo, Beijing, Nairobi. Consider what that sentence confesses. The World Athletics Championships have been staged twenty times since Helsinki in 1983. Twelve of those twenty editions were held in Europe, the most recent in Budapest three years ago. Africa, the continent that has supplied the sport's distance running for two generations, has hosted precisely none. That a British correspondent should regard three championships in a row beyond Europe's shores as a scandal, rather than as an overdue correction, tells us where his compass points. It points home. Munich will host in 2031. Europe will go eight years between championships. Africa waited forty-six years to receive its first.

A host city is not a defendant

Mr Lawton's argument rests on collapsing three things that must be held apart: the culpability of individual athletes, the performance of a national anti-doping system, and the capability of a city to stage a championship. A host city is not a defendant and a championship is not a sentence. Once those three are separated, the case against Nairobi comes apart in the hand.

If the proposition is that a country's doping record should disqualify its cities from hosting, then let it be stated as a universal rule and let its author explain how it would have applied historically. Moscow staged the 2013 championships while what the McLaren investigation would later establish as an institutionalised and systematic state doping programme was operating, one that implicated medallists at those very championships and more than a thousand Russian athletes across sports. Where was the editorial thunder from The Times demanding that Moscow be stripped? Eugene received the 2022 championships without a competitive bid at all. None of this excuses a single Kenyan doping offence. It demonstrates why individual violations, national anti-doping systems and the suitability of a host city must be analysed separately, and why a rule discovered only when the beneficiary is African is not a rule.

What the numbers actually say

The figure being brandished, 318 Kenyan athletes sanctioned since the Athletics Integrity Unit was created, is serious, and nobody defending Nairobi should pretend otherwise. But a sanctions total is simultaneously evidence of a doping problem and evidence that athletes are being detected, prosecuted and removed from competition. Kenya sits in the Integrity Unit's Category A, the tier subject to the most intensive testing in the sport, and its athletes are tested accordingly. The relevant question is therefore not whether Kenya has had a doping problem, for it plainly has, but whether that problem makes Nairobi incapable of staging a clean World Championships.

On that question the evidence runs the other way. Kenya criminalised doping by statute in the Anti-Doping Act of 2016, which vests the Anti-Doping Agency of Kenya with authority over testing, investigation, results management and prosecution. The government has committed five million dollars a year to testing and education, a commitment World Athletics itself cited this week in defending the award. Asbel Kiprop and Ruth Chepngetich were caught, charged and sanctioned. That is what a functioning system looks like. Mr Lawton offers Kenya's convictions as evidence of Kenya's guilt. A lawyer who argued that a country with many prosecutions must be lawless would be laughed out of chambers. World Athletics, for its part, has not presented Nairobi 2029 as absolution. Lord Coe said there were four outstanding bids and that the decision was difficult; the evaluation weighed government guarantees, budgets and growth potential. Nairobi won on the merits of a bid, not on the erasure of a record.

London's own scoreboard

Since the London Marathon was first run in 1981, Kenyan athletes have won its elite men's and women's races thirty-five times: twenty men's victories and fifteen women's. Eliud Kipchoge holds the men's record with four titles. This April, the greatest moment in the history of the event, the first sub-two-hour marathon ever run in open competition, was authored on the streets of London by Sabastian Sawe of Kapsabet in 1:59:30. British runners are welcomed each year to train in Iten and Kaptagat; Kenyan runners arrive each April to win in Greenwich. The sport's capital has been on the Rift Valley escarpment for decades. World Athletics has merely updated the postal address.

The galaxy of generalisation

Here is the true objection, and it must be named. Mr Lawton has taken the offences of individual athletes and draped them over fifty-five million people, a government, a city, a stadium, and a bid. That is the galaxy of generalisation. One need not speculate about Mr Lawton's motives; the asymmetry is visible in the argument itself. Individual Kenyan offenders become evidence against Nairobi. Comparable integrity crises elsewhere, Moscow above all, have not ordinarily been treated as permanent indictments of the cities and populations around them. When a European athlete falls, he falls alone; when a Kenyan athlete falls, a nation stands convicted. Whether that asymmetry is conscious or unconscious matters less than the fact that it exists, and that it has a long and unlovely history in how African achievement is reported in Britain. A standard enforced in only one direction is not a standard of integrity.

What Nairobi has already done

Kasarani hosted the World Under-18 Championships in 2017 and the World Under-20 Championships in 2021, the latter during a pandemic, and delivered both. The stadium is being rebuilt ahead of the 2027 Africa Cup of Nations. The bid was contested against London and Rome, and it won on the votes of the World Athletics Council under a president who is himself British, an Olympic champion, and the architect of the very governance reforms Mr Lawton concedes are exemplary. Lord Coe did not lose his judgment on Tuesday. He exercised it.

A closing word

Kenya does not require Mr Lawton's permission to host the world, any more than it required his permission to win London's marathon, break the two-hour barrier, or fill the medal tables of every championship he has covered. In 2029 the fastest men and women on earth will run at Kasarani, at altitude, before a crowd that knows every split, watched by a continent that has waited since 1983. Mr Lawton is welcome to attend. He will find the testing rigorous, the welcome warm, the stadium full, and Africa, after forty-six years of waiting, finally at home.

---

Dr. rer. nat. habil. Dr. Seronei Chelulei Cheison was born in Nandi County, Kenya, the birth county of Kipchoge Keino, Eliud Kipchoge and Sabastian Sawe. He writes from Langwedel, Lower Saxony, and Cheptabach, Nandi County.

Thursday, 10 September 2026

Petfood Palatability: The Physical Signals That Drive Preference

THE PHYSICS OF PETFOOD PALATABILITY

The same recipe, in a different physical state, is a different food to the animal. How much of palatability was never about the formula at all?

Take a single cut of beef, the same animal, the same muscle, and put it into four different kitchens.

In the first it is thrown onto a grill and left to char, and it comes off blackened at the edges, smoky, its surface a crust of browned reactions, eaten hot with the hands. In the second it is cut small and braised for hours until it collapses, and it arrives soft and yielding in a dark paprika gravy, the meat and the sauce by now almost one thing. In the third it is simmered gently and served in a clear rich liquor, tender pieces in a broth that carries its own separate warmth and smell. And in the fourth it is ground, salted, seeded with bacteria, stuffed and hung for months in a cool cellar until it is dense and dry and sharp, and then it is sliced thin and eaten cold.

A barbecue. A gulasch. Meat in gravy. A salami. The same animal stands behind all four. Yet no one who has eaten would call them the same food. No one wants the salami hot from a grill or the barbecue cold from a fridge in thin wet slices. We do not merely accept that these are different dinners. We feel it, in the mouth, without being taught.

So here is a question worth carrying into the rest of this essay, because the petfood industry answers it every day without quite noticing. If the same beef can become four foods that eat nothing alike, how much of what we call palatability was ever really about the recipe at all, and how much was about the state the food arrived in?

Movement I

THE OBJECT IN THE BOWL

Now carry that cow into the pet food aisle, because the same thing has happened there, and we have been much slower to admit it.

The industry does not sell one wet food. It sells a chunk in gravy, and a chunk in jelly, and a pâté, and a mousse, and a loaf, and alongside them a dry kibble that shares more with a biscuit than with any of the wet formats. These are not simply five recipes. They may share the same nutritional intention, the same protein source, the same flavour direction, and yet become radically different physical objects that an animal meets in radically different ways. The chunk must be picked up and broken. The pâté yields at once. The gravy carries smell and moisture separately from the solid it surrounds, so that a cat can, and often does, drink the sauce and leave the meat, or the reverse. The kibble is hard and dry and can deliver a disproportionate part of its immediate palatability signal from a surface rather than from its body. To the formulator these may be one product line in several presentations. To the animal they are several foods.

And this is the quiet assumption the whole category rests on, that if we get the formula right the food will follow. But the animal never encounters the formula. It encounters an object, with a temperature, a texture, a moisture, a shape in the mouth, and a smell that the physical state either locks away or sets free. The recipe is what we wrote down. The object is what the animal actually met. We have spent a great deal of this series arguing about the first, and comparatively little about the second, and the animal has been judging the second all along.

None of this is a failure of formulation. It is simply a part of palatability that sits in the physics rather than the chemistry, and that has never had the attention the chemistry receives. So the question is not whether recipe matters. Of course it does. The question is the one we rarely put to ourselves plainly. How much of the animal's verdict was shaped, from the first encounter, by the plain physical facts of how the food arrived?

The recipe is what we wrote down. The object is what the animal met.

Movement II

THE TEMPERATURE OF THE MEAL

Start with the lever that costs almost nothing and is discussed almost never. Temperature. Not the heat of cooking, which the animal never sees, but the plain warmth or cold of the food in the moment it is set down.

Anyone who has kept a cat has watched the small drama. A pouch or a can straight from the fridge is opened and spooned out, and the cat approaches, lowers its head, and declines, and the food sits congealing while the animal looks at its owner with what feels like reproach. The same food, left to reach room warmth, or briefly warmed, is eaten. Nothing in the recipe changed between the refusal and the meal. Only the temperature did. And the question that ought to follow is the one the industry rarely asks out loud. If the same food can be refused cold and eaten warm, what exactly was the cold food failing to do?

One important part of the answer, as far as the science can currently show it, is that the colder food was giving the nose less to work with. When aging cats were offered the same chunks-in-gravy product at three temperatures, chilled to 6 degrees, at room temperature near 21 degrees, and warmed to 37 degrees, they preferred the warmer food in every comparison, and the warmest most of all. What makes the study worth dwelling on is what it ruled out. The gravy's thickness barely changed across the three temperatures, so the difference was not that the cold food was harder to eat. What changed was the air above the bowl. Warming released markedly more of the volatile compounds that carry smell, including the sulfur notes associated with cooked meat and an acid tied to palatability, while some of the plant-like volatiles fell away. The cold food was not a different recipe. It was the same recipe with its aroma still locked inside it.

For a cat this may matter more than it would for us, because olfaction appears to be especially important in how a cat first investigates and accepts a food. Much of whether it approaches, and often whether it eats at all, seems to be settled by what reaches it through the air before a whisker touches the food. Warm the food and you set more of that aroma free; chill it and you hold much of it back, muffling the very signal the animal leans on for its first decision. The food that a cat meets cold is, in a real sense, a quieter food, and a quiet food asking a scent-led animal to commit is asking a great deal.

It is tempting to see an evolutionary fit here, since freshly killed prey is warm and not refrigerated, and a warmed food sits nearer that temperature than a chilled one. Whether a cat actually reads the warmth itself as part of a fresh-prey signal, rather than simply enjoying the fuller aroma that warmth releases, is a harder question than the tidy story admits, and one the evidence has not settled. What is clear is the direction, not yet the full reason.

And there is a deeper principle underneath the single study, one that belongs to physics rather than to cats. The molecules that carry smell are volatile, which is only to say that they leave the food and enter the air more readily as the food warms. Aroma release is temperature-dependent by its nature, and in humans a good deal of what we loosely call taste is really smell arriving by the back of the throat as we chew. How large that retronasal contribution is for a cat is not something we should assume from our own mouths, but the underlying physics, that warmth lifts volatiles from food, does not care whose nose is downwind. This is not a quirk of one product or one panel of elderly cats. It is true of a stew on a human stove and true of a chunk in gravy in a bowl, and it means the temperature of a food is never neutral. It is always either releasing the signal or holding it back.

Which raises something the industry knows and rarely says plainly. The animal does not choose the temperature. We do, or the room does. A pet has no fridge and no microwave and no sense of when the pouch was opened. It meets the food at whatever warmth we happen to have left it, and that warmth is doing quiet work on the aroma either way. Nor is warmth a free lever, because the same heat that frees the smell also hurries the spoiling. A wet food left out to reach an appetising warmth is also a wet food warming toward the temperatures at which it turns, and the window in which a bowl is both fragrant and safe is narrower than we like to admit. Temperature, in other words, is not a small convenience at the edge of palatability. It is a variable we control on the animal's behalf, it governs both the smell and the safety of the meal at once, and the animal lives entirely at the mercy of the choice we make for it.

We did not change the recipe. We changed how loudly it could speak.

There is a fairness in noting that the effect has been studied particularly carefully in older cats, a population in which age-related changes to smell and taste may make food presentation especially consequential. But the finding points somewhere uncomfortable for how we test and how we feed. A palatability trial run at one temperature has measured the food at that temperature and nowhere else. A diet judged wanting in the bowl may have been judged wanting cold. How much of what we have recorded as a preference for a food was, without our noticing, a preference for a temperature?

Movement III

HOW MUCH WATER

Temperature governs how loudly a food can speak. Water changes the language in which it speaks, and it does so along a spectrum most owners never think about even as they choose a point on it in the aisle.

At one end sits the dry food, a kibble holding less than about a tenth of its weight as water, closer in physical character to a biscuit than to anything an animal would meet in the wild. At the other end sits the wet food, most of its weight water, often three-quarters or more, soft and yielding and packaged in a can or a pouch because it cannot be stored any other way. And between them, less discussed and quietly interesting, sits the semi-moist food, somewhere around a fifth to a third water, soft enough to yield like meat yet stable enough to live on a shelf. Three foods, one nutritional intention, and three completely different physical propositions for the animal that has to eat them.

The industry has long observed that animals often take more readily to wet food than to dry, with semi-moist somewhere between, though the ranking is a tendency rather than a law and turns on the species, the individual, the product and the test. What is more certain, and more interesting, is that a good part of whatever difference exists is physics rather than flavour. Water is the medium in which taste-active substances dissolve and reach the tongue, so a wet food presents much of its flavour already in solution, ready to be perceived the moment it is in the mouth. Aroma is a subtler matter, because how much scent a food releases into the air depends not only on its water but on its fat, its proteins, its matrix and the particular volatile in question, and more water does not simply mean more smell. What water changes most is not whether a food has aroma but how the food organises and releases its sensory chemistry. A dry kibble is not silent; it carries scent in its headspace, which is part of why the outside of a kibble is where so much of its immediate palatability is deliberately placed. But a dry kibble carries relatively little flavour in solution until saliva begins to rehydrate it in the mouth, so a large part of its first, decisive impression has to be loaded onto its surface rather than built through its body.

That distinction, between sensory chemistry distributed through a food and sensory chemistry concentrated on its surface, is one of the most consequential facts in the category, and it follows directly from moisture. In a wet food, sensory chemistry can be distributed through the matrix. In a dry food, much of the immediate palatability signal is deliberately concentrated at the surface, so the animal meets that layer first, in the first second, dry against the tongue. The two formats are not louder and quieter versions of one food. They are two different architectures of flavour, and moisture is a large part of what decides which architecture you are building.

The flavour of a wet food is largely in the food. Much of the immediate flavour of a dry food is deliberately put on it.

The semi-moist food is the most ingenious point on the spectrum, and the reason repays a moment. Its appeal is softness and higher moisture, closer to the mouthfeel of meat than a hard kibble can manage, and yet it survives on a shelf without a can. The key is that the important number is not simply how much water a food contains, but how much of that water is free to participate in chemistry and support microbial growth, which is measured as water activity. A food can hold a good deal of water and still keep well if enough of that water is bound rather than free. Water activity is not the whole of the trick, because shelf stability also leans on solutes, acidity, preservation and packaging together. Salt is one of those solutes, and it is worth naming here because it is quietly doing physical work long before anyone asks whether it can be tasted. Dissolved in the food, salt lowers the activity of the water present, making less of it available to the microorganisms that would otherwise exploit it, which is part of why salting has preserved meat for as long as people have wanted meat to last. In a pet food, salt is one of the levers that helps hold a soft, moist texture at a moisture that would otherwise spoil. Its first job, in other words, is not flavour at all. It is physics. Water activity, then, sits at the heart of the compromise, and it lets a semi-moist food strike a clever balance, wet enough in the mouth to please the animal, stable enough in the microbial sense to keep. It shows how far the physical form alone, quite apart from the recipe, can be engineered to change what the animal experiences.

So the question that closes this lever is not which format is best, because that depends on the animal, the owner, the budget and the shelf. The question is subtler and more uncomfortable. When an animal prefers the wet food to the dry, as animals so often do, how much of that was a verdict on the flavour we formulated, and how much was a verdict on water itself, changing the way that sensory chemistry was organised, released and encountered?

Movement IV

THE SHAPE OF THE MOUTHFUL

There is a soft, semi-moist dog food, strongly aromatic and easy to mould, that anglers have quietly used for years as fishing bait. It is not hard to see why. It holds together on a hook, it releases its scent into the water, and it can be pressed into whatever shape the moment requires. Not one of those virtues has anything to do with the dog it was formulated for. They are pure physics, the properties of the object rather than the recipe, and they are compelling enough to work on a fish. A food designed for one species, doing some of its most persuasive work underwater, on another that it was never meant to feed. If the physical form of a food can do that, we should take seriously what it is doing inside the mouth it was actually built for.

Because the animal does not swallow a formula. It takes hold of an object, of a particular size and hardness and shape, and its mouth has to do something with it, and what the mouth can comfortably do differs between our two species. Dogs tend to eat quickly and bolt much of what they are given. Cats tend to take smaller bites and spend longer over a meal, and their jaws do not move sideways to grind; their teeth are built to shear and tear. That anatomy is part of why texture, size and shape appear to weigh more heavily for cats than for dogs, and why a cat is quicker to reject a piece that does not sit right in the mouth. For the cat, texture is often not a finishing touch on palatability. It can be a gate the food has to pass through before taste is ever consulted.

The consequences are surprisingly specific. How a kibble behaves in the mouth is a question of food mechanics, of its hardness and brittleness and the force needed to fracture it, and those depend on many things at once, on density and porosity and moisture and the way it was made, as well as on its size and shape. A cat that must break every piece with shearing teeth is sensitive to the result. Shape matters too, and not decoratively; a kibble with sharp edges can be awkward to grasp and uncomfortable to bite, and there are indications that cats favour rounded, easily handled forms, some so specifically that flat-faced breeds are offered kibbles shaped to be caught more easily by a short muzzle. Lower-density pieces that fracture readily tend to be appreciated. None of these are matters of flavour. They are matters of how the object meets the mouth, and where the fit is wrong the flavour may never get its hearing.

For the cat, texture is not the finish on palatability. It is the gate it has to pass first.

Salt belongs in this movement too, and not for the reason a human cook would expect. On our side of the bowl, salt earns its place partly by changing the food as a physical material, drawing out and dissolving proteins, altering how a mixture binds and sets and holds together, shaping the very texture we have been talking about. But cross to the animal's side and the familiar human logic loosens. Experimental work suggests that cats do not show the straightforward attraction to added salt that humans do, and that sufficiently high concentrations become aversive to them, so that even a sodium-depleted kitten will not reliably choose a salted diet over an unsalted one. One plausible explanation lies in their carnivorous history. An animal whose ancestral diet supplied its sodium through animal tissue may have faced a very different selection pressure from omnivores repeatedly meeting sodium scarcity, though whether that fully explains the feline response is harder to establish. What matters here is the practical point. Salt can be technologically important to the food, doing real work on its water and its texture, without functioning as the simple flavour reward a human cook would assume, which is one more sign of how far the animal's palate has diverged from the one we keep, without noticing, projecting onto it.

We salt our food for pleasure. For the cat, salt plays by different rules.

Wet food is where physical form becomes almost a language of its own, because here the same nutritional intention can be presented as a smooth pâté that yields at once, or a firm loaf that must be broken, or discrete chunks suspended in a gravy, or the same chunks set in a jelly, or a whipped mousse. These are not decorative distinctions. A pâté asks nothing of the teeth and gives its flavour immediately. A chunk asks to be seized and sheared and holds its flavour in a body the animal has to work into. And the chunk formats do something stranger still, because the chunk and its surrounding gravy or jelly are, in effect, two foods in one bowl, a solid and a sauce with their own separate textures and their own separate loads of smell and flavour. Watch a cat lick every trace of gravy from around the chunks and walk away, or clean up the chunks and leave the jelly congealing at the edges, and you are watching something precise. On the label there was one product. In the formulation system there was one recipe. In the bowl, the animal ran its own separation and chose. The manufacturer made one food. The cat found two.

The manufacturer made one food. The cat found two.

So the uncomfortable question that this lever leaves is the same one the others keep raising, in a new costume. When a cat turns from a food, we are inclined to record that it did not like the taste. But how often had the taste even been reached? How often was the refusal a verdict passed at the lips, on a piece too large or too hard or too sharp or too oddly shaped to be worth the trouble, delivered long before a single flavour molecule was ever given the chance to make its case?

Movement V

THE ACID EDGE

The last of the physical levers is the quietest, and the one that sits closest to the border between physics and chemistry, which is why it is worth handling carefully. The acidity of a food, its pH, is not a flavour in the way that a savoury peptide is a flavour. It is a condition of the whole food, a property of its water and its salts, and it shapes how the food is perceived without being an ingredient the animal could point to.

Cats, the palatability literature suggests, do care about it. Given a choice they tend to prefer a mildly acidic food over a neutral or an alkaline one, and acidulants are used in cat foods partly for that reason. One reading of why is evolutionary, that a carnivore eating fresh meat and organs is eating mildly acidic material, so a food in that range reads as right. That is a plausible interpretation rather than a settled fact, but the preference itself is real enough to matter to anyone formulating for cats. So far this looks like one more thing we could simply add and be done with.

But the lever has a hinge in it, and the hinge is the interesting part. The same cat that is drawn to a mild acidity will refuse a strong sourness. A sharply sour taste is aversive to cats, as it is to many animals, one of the signals a cautious eater treats warily. It is tempting to tie this neatly to spoilage, to say that sourness means rot, but the chemistry of decay is not that tidy. Spoiling food can turn more acidic when certain bacteria produce acids, and it can turn more alkaline when others release amines and ammonia from breaking-down protein, and it throws off sulfur compounds and other volatiles besides. Rising sourness is one possible sign among several, not a clean dial from fresh to foul. What we can say more safely is narrower and still useful. Cats like a little acid and reject a lot of it, so pH is not a setting you can push in one direction for more reward. It is a window, and both of its edges matter.

There is, separately, a real fact about acid and keeping. Lowering a food's pH is one of the oldest ways of preserving it, because many of the microbes that spoil food grow poorly as acidity rises, which is why acidified and fermented foods keep where neutral ones do not. So on the food's side, acidity is partly a preservation tool. Whether the animal's own taste for mild acidity evolved as a freshness cue, or for some other reason, or as a mixture of causes, is less certain than the neat story would have it. It is enough to notice that acid does real work on two fronts at once, on how long a food lasts and on whether a cat will accept it, and that a formulator has to satisfy both.

Step back and the physical levers we have walked through share a quality worth naming. Each of them is a case of the same thing: physics deciding how the chemistry of a food reaches the animal, or whether it reaches the animal at all. Temperature governs how much of the aroma leaves the food for the air. Water, and how much of it is free, governs how flavour dissolves and travels and how the food keeps. Texture and geometry govern whether the mouth can comfortably process the piece at all. Phase, the chunk and its separate sauce, governs whether the animal can take one part and leave another. And pH shifts taste, protein state, preservation and the food's chemical equilibria all together. None of these is the flavour. All of them decide what becomes of the flavour on its way to being judged. The recipe lists what is in the food. Physics settles what the animal actually gets.

We have brushed against this before in these Conversations, and only now does it show its shape. An earlier one followed fat down the road of oxidation and found that the same molecule which signals a fresh kill signals rancidity a few steps later, so that the animal is not reading whether the fat has oxidised but how far along the reaction has run. That was a story about how a chemical signal is presented to the animal in time, and this is the same story told in space and state, about how a whole food is presented to the animal in the physical form we give it. In both, the thing we call palatability turns out to live not purely in the composition, but in the meeting between a food in a particular state and an animal equipped to read it.

And here the physical lever quietly becomes a clinical one, which is a pattern this series keeps meeting. A cat's urinary health depends on the acidity of what it eats, because a diet that pushes the urine too far in one direction invites one kind of stone and too far in the other invites another. So the pH of a cat food is never chosen for palatability alone. It is chosen at the meeting point of what the cat will find attractive, what will keep it from harm, and what the food's own ingredients and preservation will allow. The window that palatability wants and the window that health requires are not guaranteed to be the same window, and the formulator lives in the overlap.

There is a last thing pH reveals, and it reframes the whole essay. The cat works with a relatively sparse gustatory apparatus, only a few hundred taste buds where a dog has thousands and a human more still, and it lacks a working sweet receptor entirely. Yet it remains one of the most discriminating animals we formulate for, the quickest to refuse, the hardest to please. That is not a contradiction. It is a warning against equating palatability with taste. The tongue is only one member of the committee, and for the cat, evidently, not the loudest. Smell, temperature, texture, geometry, the acidity the animal will accept only within a narrow band, the physical state of the food in every respect we have walked through: all of them get a vote. And all of them are, in one way or another, physics.

So the question this final lever leaves is the largest one. We have spent a career, as an industry, refining the flavour of foods for an animal that judges as much by other means as by the tongue. How much of the palatability we have been chasing was ever really in the flavour at all, and how much was waiting, all along, in the physical state of the food, in the plain facts of how warm it was, how wet, how hard, how shaped, and how sour, before the tongue was ever asked for its weak and final opinion?

Movement VI

THE SAME COW

Return, at the end, to the four kitchens.

The barbecue and the gulasch and the salami were the same cow, and no one who ate them was fooled into thinking they were the same dinner. We knew, in the mouth, that the fire and the braise and the ferment had made three different foods out of one animal, and we never once mistook the recipe for the meal. We grant ourselves that distinction without a thought. We have been slower to grant it to the animal in the bowl.

Because the pet food industry has spent most of its ingenuity, and most of these Conversations, on the recipe: the protein, the fat, the palatant, the chemistry of the thing. All of that is real and none of it is wasted. But the animal has never eaten the recipe. It has eaten an object, warm or cold, wet or dry, soft or hard, sharp or mild, and it has judged that object with its whole body, its nose and its mouth and its long inheritance of caution, well before the tongue was ever consulted. The formula was our question. The object was the animal's answer.

None of this asks us to think less of flavour. It asks us to notice how much of what we credited to flavour was being carried, quietly, by the plain physics of the food. And it suggests a way of holding the two together that does not make them rivals. Chemistry supplies the signals a food can send, the savoury peptide, the fresh-kill volatile, the amino acid the tongue is tuned to. Physics decides when, where and in what state those signals reach the animal, or whether they reach it at all. Physical form, in this light, is the delivery architecture of palatability. Chemistry writes the message. Physics controls its delivery.

Chemistry writes the message. Physics controls its delivery.

And it is worth pausing on the strangest thing of all, which is how the animal reads that delivery. The cat carries no pH electrode and no thermometer, no hygrometer to weigh the moisture and no instrument to measure the hardness of a piece or the water activity of a paste. It does not measure these properties one at a time. It encounters their consequences together, in the few seconds between approaching the bowl and eating or turning away. Our instruments separate the food into variables, temperature here, moisture there, acidity, hardness, geometry, each on its own dial. The animal integrates them into behaviour. And that behaviour is the only answer we ultimately receive. The food arrives whole. The animal answers whole. We are the ones who divide both into measurements.

We have spent these Conversations taking the food apart. We have looked at the volatile that announces a fresh kill, the fat that carries its own clock of freshness, the plasma that holds a chunk together, and the enzyme that cuts a protein until savour and bitterness begin to trade places. All of it matters, and none of it reaches the animal in the abstract. It arrives warm or cold, wet or dry, dissolved or held fast, on a surface or inside a body, in a chunk that fractures, a gravy that can be licked away, a jelly that keeps its water still, or a pâté in which there is nowhere for one part to hide from another. The same cow can be four dinners. The same formula can be five foods, because a formula has no temperature, no bite and no mouthfeel until we turn it into something an animal can actually eat.

The recipe tells us what we made. The animal only ever meets what it became.

References

1. Eyre, R., Trehiou, M., Marshall, E., Carvell-Miller, L., Goyon, A. & McGrane, S. (2022). Aging cats prefer warm food. Journal of Veterinary Behavior 47:86-92. doi:10.1016/j.jveb.2021.09.006

2. Bradshaw, J.W.S., Goodwin, D., Legrand-Défretin, V. & Nott, H.M.R. (1996). Food selection by the domestic cat, an obligate carnivore. Comparative Biochemistry and Physiology Part A 114(3):205-209. doi:10.1016/0300-9629(95)02133-7

3. Cook, N.E., Rogers, Q.R. & Morris, J.G. (1996). Acid-base balance affects dietary choice in cats. Appetite 26(2):175-192. doi:10.1006/appe.1996.0014

4. Yu, S., Rogers, Q.R. & Morris, J.G. (1997). Absence of a salt (NaCl) preference or appetite in sodium-replete or depleted kittens. Appetite 29(1):1-10. doi:10.1006/appe.1996.0088

5. Fettman, M.J., Coble, J.M., Hamar, D.W., Norrdin, R.W., Seim, H.B., Kealy, R.D., Rogers, Q.R., McCrea, K. & Moffat, K. (1992). Effect of dietary phosphoric acid supplementation on acid-base balance and mineral and bone metabolism in adult cats. American Journal of Veterinary Research 53(11):2125-2135.

6. Hagen-Plantinga, E.A., Orlanes, D.F., Bosch, G., Hendriks, W.H. & van der Poel, A.F.B. (2017). Retorting conditions affect palatability and physical characteristics of canned cat food. Journal of Nutritional Science 6:e23. doi:10.1017/jns.2017.17

7. Calderón, L.A. et al. (2024). Measuring palatability of pet food products: sensory components, evaluations, challenges, and opportunities. Journal of Food Science 89(9):5359-5382. doi:10.1111/1750-3841.17511

8. Shin, T., Nahm, I., Maeyama, T., Miyazaki, J., Matsuo, H. & Yu, Y. (1995). Morphological study of the laryngeal taste buds in the cat. The Laryngoscope 105(12):1315-1321. doi:10.1288/00005537-199512000-00010

Thursday, 24 September 2026

Petfood palatability in veterinary diets: what the patient will eat

THE COLOURS THE DISEASE REMOVED

FOUR WAYS TO BREAK THE AGREEMENT

MORE IS NOT THE ANSWER

THE FIRST MOUTHFUL

References

About the Author

Thursday, 17 September 2026

Petfood palatability: Why amount eaten under-measures liking

THE EMPTY BOWL

EATS TO LIVE

THE DIET THE ANIMAL NEEDS MOST

WHAT WE MEASURE

WHAT WE DISCARD

BEYOND THE BOWL

References

About the Author

Wednesday, 16 September 2026

The Galaxy of Generalisation: A Reply to Matt Lawton

Thursday, 10 September 2026

Petfood Palatability: The Physical Signals That Drive Preference

THE OBJECT IN THE BOWL

THE TEMPERATURE OF THE MEAL

HOW MUCH WATER

THE SHAPE OF THE MOUTHFUL

THE ACID EDGE

THE SAME COW

References

About the Author

Petfood palatability in veterinary diets: what the patient will eat