Kitchen Mysteries_ Revealing the Science of Cooking Part 1

Kitchen Mysteries.

Revealing the Science of Cooking.

by Herve This.

Series Editor's Foreword

As an ever-curious if scientifically untrained food lover and sometime home sous-chef, I have long sought to grasp the rationale that science might offer to explain the not-infrequent disasters I have produced in my unscientific and amateurish cooking. Thanks to Herve This, I discovered that I could live with the pitfalls as long as failure could become a learning experience.

What makes microwave heat so different from gas-fired ovens that it causes a tarte Tatin tarte Tatin to go all soggy? Why did that souffle fail to rise, what diabolical chemistry caused my bearnaise to liquefy? Call Herve This. He is our necessary navigator over microwaves and through formerly murky seas of culinary science. to go all soggy? Why did that souffle fail to rise, what diabolical chemistry caused my bearnaise to liquefy? Call Herve This. He is our necessary navigator over microwaves and through formerly murky seas of culinary science.

The chef's domain is a Faustian alchemist's laboratory. As Herve This demonstrates charmingly and convincingly, the mysterious transformations created there rely on predictable chemical or physiological reactions that we know how to bring about, avoid, or remedy (though we be ignorant of the scientific principles behind the phenomena). But chefs and cooks, whether amateur in the home kitchen or professional behind the stoves, anyone, in short, with more than the slightest curiosity, should want to know how things work. The incontrovertible laws of chemistry and physics are here made accessible, and their practical application demonstrated.

Why is the crust of bread tastier than the crumb? Are prosciutto and other salt- or air-cured pork products really safe? How does the chemistry of salt and air "cook" a ham? Why is the decomposition brought about by the enzymes in marinades a form of chemical creativity? By what chemical process does a fine red wine become "corked"? Under a manifesto of total accessibility, Herve This offers his reader "popular [culinary] science" in brief chatty chapters resembling sound bites from his famous TV shows. Overcoming whatever potential intimidation his use of basic scientific terms might arouse, Herve This writes in a style both endearing and dignified, combining science, cultural history, and humor. Kitchen Mysteries: Revealing the Science of Cooking Kitchen Mysteries: Revealing the Science of Cooking is a worthy companion to is a worthy companion to Molecular Gastronomy Molecular Gastronomy, the author's first book in our series Arts and Traditions of the Table.

"Molecular gastronomy": a culinary buzzword for the new millennium? In the last decades of the twentieth century controversies as to what const.i.tuted "nouvelle cuisine" or, later, "fusion cooking" inspired a veritable litany of protests from chefs denying their adhesion to such perhaps ephemeral fas.h.i.+ons. Methinks they doth protest too much.

Today, "I don't do molecular gastronomy" has become a much intoned protest song for those reluctant to join in the avant-garde chorus led by Ferran Adria, Pierre Gagnaire, Charlie Trotter, and Heston Blumenthal, to name but the most prominent innovators of a cuisine that some have called "cuisine scientifique" and others "deconstructive." (Mind you, Heston and the others never actually did Molecular Gastronomy, because MG is science. In the beginning, some chefs did "Molecular Cooking," and many others are still doing it, in spite of the fact that Heston and Ferran have now moved to culinary art instead of using the technological applications of MG. Deconstruction is another story, nothing to do with MG or Molecular Cooking.) These great pract.i.tioners of what is in fact a panoply of variegated cuisines share a spirit of scientific inquiry. They are chefs who w.i.l.l.y-nilly combine their art with science (caution: applied science cannot exist because if it is science, it's not applied, and if it is applied, it's not science but technology). No chef actually practices science, of course; they engage in a craft, because they have to produce: the kitchen is, after all, a laboratory. There, inevitably, chemical and physics experimentation is constantly under way. For example, as This emphasizes, a question ceaselessly raised and tested has to do with the ongoing importance of Maillard reactions (the action of amino acids and proteins on sugar), or what makes foods change color, to what degree does heat transform tastes or aromas? In the cooking process, a chef has to ask how to keep the primary colors of vegetables intact. What is the scientific explanation for those methods? Indeed, why do certain procedures work or inevitably fail?

Herve This examines the why behind kitchen rituals. He makes complex science easy to grasp for nonscientists and the general reader. Here we have science and history at the service of the practical in a veritable physiology of taste, one worthy of the first promulgator of gastronomic science, Brillat-Savarin!

Albert Sonnenfeld

Cooking and Science.

Venial Sins, Mortal Sins.

"Add the cheese bechamel to the egg whites, beaten into stiff peaks, without collapsing them!" Such vague instructions in a souffle recipe often make amateur cooks nervous. How to avoid collapsing those laboriously beaten egg whites? In our ignorance, we begin by using what we think is a gentle-that is, slow-technique. The egg whites and the bechamel do not mix easily, so we stop before we have a h.o.m.ogeneous blend or we stir the two ingredients so long that the egg whites collapse. In both cases, the effect is the same: the souffle is ruined.

Where does the fault lie? With the cookbook that takes for granted such simple techniques, known to professionals but not sufficiently mastered by the general public? With the neophyte, who naively, even presumptuously, ventures into a discipline that is not so simple as it seems?

Difficulties like those encountered in preparing a souffle do not jeopardize our access to the realm of taste, and even the cookbook's scant instructions mark only a venial sin. With a little research, the novice will soon track down an explanation of the basic culinary techniques, and, rea.s.sured, she or he will come around to accepting-even to wis.h.i.+ng-that cookbooks not all repeat the same advice, which he once considered them to be lacking.

On the other hand, more troubling, it seems to me, are such terse phrases as "Mix the egg yolks two by two into the cheese bechamel sauce thus prepared." Why two by two? And why not six at once if I am in a hurry? This time, the explanation is nowhere to be found. Experience alone demonstrates the validity (or not!) of the advice. A few attempts to break the rule will return the audacious cook to the wisdom of the ancients, but he will remain intellectually frustrated if he is as curious as he is epicurean.

In this work, I want to share with you the explanations that science offers for those empirical precepts handed down from chef to chef and from parent to child. Better understood, the bits of advice and suggested techniques that cookbook authors offer in pa.s.sing will be better respected. Knowing the reasons behind them, you will be able to follow recipes considered difficult for their thousands of "fundamental trifles" and achieve results you never expected. You will learn to adapt recipes to the ingredients available to you; sometimes you will even modify proposed techniques according to the available utensils. Feeling equal to the task, you will be more confident and more relaxed, and you will be able to call into play all your innate creativity.

Canard a la Brillat-Savarin To whet your appet.i.te by giving you the chance to verify that an infusion of science can have its usefulness in cooking, I offer you a recipe that compensates for the inadequacies of the microwave: a quick canard a l'orange canard a l'orange.

Who has not taken a bland, gray, tasteless piece of meat from his microwave? Should we prohibit the use of microwaves for cooking meat and restrict them to reheating prepared dishes? It would be a shame to deprive ourselves of their advantages (quick, economic, energy-efficient cooking), but we must learn the specific possibilities this new kind of cooking offers, so that we do not ask it for more than it can give. As the old, politically incorrect proverb says, even the most beautiful woman in the world can only give what she has.

Microwave cooking is no great mystery. Very simply, microwaves heat the specific parts of food that contain lots of water. In other words, if we are not careful and put a piece of meat in a microwave oven, we will only succeed in steaming it. What a shame to turn duck or beef tenderloin into stew!

Why are microwaves so deficient when used in this way? Because they skip over one of the three fundamental functions of cooking. Cooking must, of course, kill microorganisms and make tough, fibrous, or hard-to-digest foods a.s.similable. But it must also make food taste good.

If grilling works wonderfully, it is precisely because it fulfills these roles simultaneously. First, the surface of the meat hardens because the surface juices evaporate while the meat proteins coagulate. Second, the meat's const.i.tuents react chemically to form vividly colored molecules but also odorant or tasty ones. In other words, a flavorful and colored crust is formed. Within the piece of meat, the collagen molecules that toughen the meat are broken down.1 The meat becomes tender. If the meat is seared, that is, cooked quite rapidly, the juices at its center do not disperse too much toward the exterior, and the meat retains its succulence and its juiciness. Biting into the meat will break the muscle fibers so that internal juices are released, bathing the mouth in a wave of delicate sensations. The meat becomes tender. If the meat is seared, that is, cooked quite rapidly, the juices at its center do not disperse too much toward the exterior, and the meat retains its succulence and its juiciness. Biting into the meat will break the muscle fibers so that internal juices are released, bathing the mouth in a wave of delicate sensations.

Let us recognize in pa.s.sing some princ.i.p.al chemical reactions in cooking, Maillard reactions, to which I will often return in this book: acted upon by heat, the molecules of the family to which our table sugar belongs (wrongly called carbohydrates, because these compounds are not strictly speaking made of carbon and water) and amino acids (the individual links in those large protein molecules) react and produce various odorant and tasty molecules. In cooking, this is one of the reactions we utilize to add savor even when we do not add flavorings to our dishes.

To make a canard a l'orange canard a l'orange worthy of its name, the microwave will not suffice. Since microwaves heat water in particular and do not increase internal temperatures to more than 100C (212F, the boiling point of water) in ordinary culinary conditions, they do not promote Maillard reactions. In the worthy of its name, the microwave will not suffice. Since microwaves heat water in particular and do not increase internal temperatures to more than 100C (212F, the boiling point of water) in ordinary culinary conditions, they do not promote Maillard reactions. In the canard a la Brillat-Savarin canard a la Brillat-Savarin that I am suggesting you make, the microwave will only be used for the braising, after a quick turn in the frying pan. that I am suggesting you make, the microwave will only be used for the braising, after a quick turn in the frying pan.

Control your desire to discover this much antic.i.p.ated recipe and grant me a few lines to introduce you briefly to the one to whom I have dedicated it, one of the greatest gastronomes of all time, the author of the Treatise on the Physiology of Flavour Treatise on the Physiology of Flavour, which every gourmand ought to have read.2 His mother was a blue ribbon chef named Aurore (hence the name of the sauce), but Jean-Anthelme Brillat (1755-1826) took the name Savarin from one of his aunts, as a condition for becoming her heir. Because of the French Revolution, his was a turbulent career. After spending some time in exile in the United States, he returned to France, where he was named adviser to the French Supreme Court in 1800. Two years before his death, he published the book that made him famous and from which I will draw many precepts, quotations, and anecdotes in the pages that follow.

Now for that duck recipe. Begin with thighs that you have grilled in clarified b.u.t.ter over a very hot flame but for a very short time, long enough to allow a lovely golden crust to appear. The clarification of b.u.t.ter, that is, melting b.u.t.ter slowly and using only the liquid fatty portion of the melted product, is useful as b.u.t.ter thus treated does not darken during cooking. After the first grilling process, the meat is still inedible because the center remains raw, and we know that duck must be cooked! Using a paper towel, blot the fat from the surface of the thighs, and, using a syringe, inject the center of the meat with Cointreau (better yet, with Cointreau into which you have dissolved salt and infused pepper). Place the thighs in a microwave for a few minutes (the precise amount of time will vary according to the number of pieces and the power of the oven). During the cooking process, the surface of the meat will dry slightly and need no further treatment. On the other hand, the center of the meat will be "braised" in an alcohol vapor and flavored with orange (my own personal taste also prompts me to stud the flesh with cloves before microwaving it).

Spare yourself the trouble of making a sauce: it is already in the meat. No need to flambe: the alcohol has already permeated the flesh. Check your watch: you will see that putting science to work has cost you no time; quite the contrary. Furthermore, it has rejuvenated an old recipe by making it lighter.

Horresco Referens 3 3 If the book you are now holding in your hands explains a few mysteries of cooking, it nevertheless sheds no light on many areas. Foods are a complex mix, hard to a.n.a.lyze chemically. For example, Maillard reactions operate simultaneously in hundreds of compounds. The chemical combinations are countless, as are the products formed. And certain molecules present in minimal concentrations in foods perform brilliant solo parts in the grand symphony of flavors.

The natural world is so rich that cooking will always remain an art, in which work and intuition will sometimes lead to miracles. A plant like sage, for example, contains more than five hundred odorant compounds. Many a roux will thicken in our saucepans before we ever determine the exact role of these compounds in the flavor. Simple calculations show that the exploration of food combinations, compounds, and flavors will never come to an end.

So does science have no place in the kitchen? Not at all! The knowledge it produces offers simple principles that apply to the different cla.s.ses of food. It explains many procedures. What you will discover here is the useful information it can provide us for eating well.

This book is not concerned with the composition of food, however. Dietary books annoy gourmands because their immediate objective is not gustatory pleasure. Often the long lists of ingredients, the tables of food const.i.tuents, in terms of fats, carbohydrates, proteins, and trace minerals, serve no purpose because they do not help answer the main question: how do the various culinary operations transform foodstuffs? How do these operations simultaneously render fibrous or indigestible foodstuffs not only a.s.similable but also delicious?

In one chapter of his book, Brillat-Savarin writes, "Here I meant to insert a little essay on food chemistry, and to have my readers learn into how many thousandths of carbon, hydrogen, and so forth, both they and their favorite dishes could be reduced; but I was stopped by the observation that I could hardly accomplish this except by copying the excellent chemistry books which are already in good circulation."4 Is that really what stopped the great gastronome? Or, rather, was he applying the maxim he gives in his introduction? "I have barely touched on the many subjects which might have become dull." Is that really what stopped the great gastronome? Or, rather, was he applying the maxim he gives in his introduction? "I have barely touched on the many subjects which might have become dull."5 Reactions in the Saucepan Having considered what this book's subject will not be, let me move on to its central theme: science and cooking. Cooks are rarely scientists, and sometimes science frightens them. Nevertheless, the marvelous thing about science is that its subjects and its laws are simple. Notwithstanding a few explorations into the composition of matter, it asks us only to accept that our universe is composed of molecules, which in turn are composed of atoms.

That we have known since middle school. We also know that atoms are linked by chemical bonds, more or less strong according to the types of atoms. Among the atoms in a single molecule, these forces are generally strong, but between two neighboring molecules, they are weak. Often when a substance is heated moderately, only the bonds between neighboring molecules are broken. Water in the form of ice, for example, is a uniform arrangement of water molecules.

When ice is heated, the energy supplied is enough to break the bonds between the water molecules and create a liquid in which the molecules still form a coherent ma.s.s but move in relations.h.i.+p to one another.

In the liquid created in this way, the molecules themselves are not transformed. The water molecules in the liquid water are identical to the water molecules in the ice. Then, as the water is heated further, it evaporates more and more, until it boils at 100C (212F), under ordinary pressure. The energy provided is enough to overcome the forces of cohesion binding the water molecules.

Again, however, in each molecule, the oxygen atom remains linked to two hydrogen atoms. This type of transformation is physical, not chemical, in nature. The water molecule remains a water molecule.

What the cook must keep in mind, however, is that foods are sometimes heated so much that chemical reactions can be produced as well. That is, molecules can be broken up and atoms rearranged, creating new molecules. I have already mentioned Maillard reactions, but they are not the only kind. Foods are chemical mixtures (and what is not a chemical mixture in our environment?), and the qualities we attempt to modify through cooking are manifestations of the chemical properties of these mixtures. When odorant compounds form on the surface of a roast, that is the result of a chemical reaction. When mushrooms darken after being cut, that is the result of a chemical reaction (enzymatic, but we shall return to this).

One reaction? Rather, a set of countless reactions, but we may simplify the a.n.a.lysis by using the biochemical cla.s.sifications: carbohydrates, fats, proteins, water, mineral elements. The austerity of this decomposition allows for an overall understanding of the phenomena. Food chemistry is still in its infancy, and chemists are working hard to discover which reactions take place in foods. They are still only seeing the tip of the iceberg. We are very ignorant about the chemistry of cooking.

Universal Gastronomy Nevertheless, there are some famous forerunners. In the mid-eighteenth century, the French cook Menon referred to the "art" of cooking, insisting on the need for experience and theory. In 1681, Denis Papin (1647-1712) invented the pressure cooker in the process of trying to discover a way to make stock from bones. The English philosopher Francis Bacon gave his life for cooking by trying to take advantage of a snowstorm to study the preservative effect of the cold. He stopped at a farm, bought a chicken, and stuffed it with snow. But he caught cold during the experiment and died of bronchitis fifteen days later.

Brillat-Savarin surveyed the scene in his time, and his admirable treatise contains a few errors that I will occasionally rectify, always paying tribute to the old master. On the other hand, I will not discuss the doc.u.ments of the microbiologist Edouard de Pomiane (1875-1964). Pomiane was very popular in the 1930s, writing best sellers and creating one of the first radio programs focusing on questions of science and cooking. He believed he had invented a new science, which he called gastrotechnie gastrotechnie, or gastrotechnology. This "science" encompa.s.sed nothing more than what Brillat-Savarin had already considered in his definition of "gastronomy": "Gastronomy is the intelligent knowledge of whatever concerns man's nourishment."6 (Incidentally, it is not generally known that the word "gastronomy" comes from the t.i.tle of a Greek work, (Incidentally, it is not generally known that the word "gastronomy" comes from the t.i.tle of a Greek work, Gastronomia Gastronomia , written by a contemporary of Aristotle, Archestratus, who had compiled a kind of , written by a contemporary of Aristotle, Archestratus, who had compiled a kind of Michelin Michelin guide for the ancient Mediterranean area; Joseph Berchoux [1765-1839] introduced the word into French in 1800.) guide for the ancient Mediterranean area; Joseph Berchoux [1765-1839] introduced the word into French in 1800.) Today, the science of cooking is progressing thanks to methods of a.n.a.lysis perfected in the last few decades that can detect compounds present in minuscule concentrations that nevertheless play a major role in the flavor of foods. Yet it remains true that we know the temperature at the center of the planets and the sun better than the temperature at the heart of a souffle. One of the cofounders of the scientific discipline called molecular gastronomy (the other being myself), the late Nicholas Kurti (1908-1998), a physicist at Oxford University and a member of London's very old and very respectable Royal Society, reminds us of this paradoxical fact. How to explain the paradox? I tend to think that we sometimes fear that cooking does not fall within chemistry's domain.

As proof, I offer an experiment carried out among friends, to "improve" wines. The physical chemist at Dijon's Inst.i.tut National de la Recherche Agronomique (INRA), Patrick Etievant, had discovered that two important molecules in the flavor of well-aged burgundy were paraethylphenol and paravinylphenol. I acquired these molecules from a chemical products retailer, planning to add them to a poor-quality wine. The only comment I got from my guinea pigs was: "That smells like a chemical." An astonis.h.i.+ng remark, because isn't everything a chemical? The foods we eat, the tools we cook with, we ourselves?

Well, it is time to discover the very substance of cooking, avoiding remarks like "it is methylmercaptan that makes urine smell after eating asparagus." What puts us off here is less the trivial nature of the remark than its uselessness in terms of cooking. To know that asparagus contains methylmercaptan does not help us cook it. Likewise, to know that the external parts of potatoes contain alkaloids like solanine or chaconine simply allows us to eat better, not to cook better. This book aims only to promote the latter.

In this book, I examine the proven techniques, a.s.semble the physical and chemical explanations, and do my a.n.a.lyses, seeking to understand without always believing that the solution given is definitive. Excuse this guide's inadequacies if you discover any, and, through your letters, help me compile improvements for the next edition. In doing this, you will be helping all gourmands, of which, naturally, I am one. Finally, please excuse me for sometimes being a bit academic. Like Brillat-Savarin, I am well aware that to speak without pretension and to listen with kindness, that is all that is necessary for time to flow sweetly and swiftly.

My huge regret is my inability to explain the genius of the great chefs, gifted with a sixth sense for harmonizing ingredients and creating unexpected a.s.sociations and surprisingly happy combinations. A veal scallop to which one adds, at the end of the cooking, a little white wine to deglaze the pan ... and a drop of pastis? The miracle happens: a superb taste emerges. The art of cooking is not a matter of succeeding with the souffle every time but of suspecting that pastis will transform a veal scallop. The rest is just the first course in cooking.

Mysterious as it is to many of us, this first course in cooking is indispensable if we are to devote ourselves to the study of tastes and flavors without being afraid of the bearnaise sauce turning or the souffle collapsing on us at the last minute. When we master these things, we can follow in the footsteps of our great forebears.

The New Physiology of Flavor The Prehistory of Tastes Before digging into the main course-the methods of preparation-let us make a little detour useful to understanding how we eat, because we will be better cooks if we know how to distinguish the various sensations that dishes produce: tastes and flavors, colors, scents, aromas.

Aristotle knew everything, but what did he know about tastes? Let us entrust ourselves to this old philosopher. Tirelessly traversing the lyceum with his disciples, he worked up an appet.i.te and turned his metaphysical mind toward gourmand meditations: there are "in the tastes as in the colors, on the one hand, the simple kinds which are also the opposites, that is, the sweet and the bitter; on the other hand, the kinds derived either from the first, like the unctuous, or from the second, like the salty; finally, halfway between these last two flavors, the sour, the pungent, the astringent, and the acid, more or less; these seem to be, in effect, the different tastes."

Aristotle is not the only authority to have appreciated oral sensations. In particular, in the eighteenth century the great Linnaeus also applied his talents to tastes, but paradoxically the most famous of systematicians, the father of botanical cla.s.sification, lacked some systematic spirit, because he mixed together the moist, the dry, the acid, the bitter, the fatty, the astringent, the sweet, the sour, the viscous, the salty. He put them all pell-mell in the same bag for us, this mix of tastes and mechanical sensations.

A Frenchman deserves the credit for establis.h.i.+ng a little order in the domain of oral impressions. In 1824 the great chemist Michel-Eugene Chevreul (1786-1889), famous especially for his work on fats, distinguished the olfactory, gustatory, and tactile sensations. He recognized that the perception of hot or cold is distinct from that of sweet or bitter. He separated out the tactile sensations of the oral cavity, as well as the proprioceptive sensations (for example, toughness). With Chevreul, the taste of physiologists-one component of flavor-was distinguished from everyday sensation, where all the sensations a.s.sociated with the absorption of food and drink are mixed.

In the same period but in a different circle, among the gourmands centered around Brillat-Savarin, the only confusion that continued to reign was between tastes and smells. The tongue was known to perceive tastes, but the nose was also believed to be a receptor. Apart from a few more or less harmless errors, the remarks made in the Treatise on the Physiology of Taste Treatise on the Physiology of Taste are as insightful as their author is pa.s.sionate about cooking: "The number of tastes is infinite, since every soluble body has a special flavor which does not wholly resemble any other.... Up to the present time there is not a single circ.u.mstance in which a given taste has been a.n.a.lyzed with stern exact.i.tude, so that we have been forced to depend on a small number of generalizations such as are as insightful as their author is pa.s.sionate about cooking: "The number of tastes is infinite, since every soluble body has a special flavor which does not wholly resemble any other.... Up to the present time there is not a single circ.u.mstance in which a given taste has been a.n.a.lyzed with stern exact.i.tude, so that we have been forced to depend on a small number of generalizations such as sweet sweet, sugary sugary , , sour sour, bitter bitter, and other like ones which express, in the end, no more than the words agreeable agreeable or or disagreeable disagreeable."7 On the other hand, a bit later, Brillat-Savarin adds that "any sapid substance is perforce odorant." On the other hand, a bit later, Brillat-Savarin adds that "any sapid substance is perforce odorant."8 He had forgotten that some molecules that are hardly volatile at all at ambient temperatures and thus odorless nevertheless bind easily to taste receptors on the tongue and palate and therefore have a taste. Salt, for example, is sapid but odorless. He had forgotten that some molecules that are hardly volatile at all at ambient temperatures and thus odorless nevertheless bind easily to taste receptors on the tongue and palate and therefore have a taste. Salt, for example, is sapid but odorless.

Modern Meanderings and Recent Revelations In trying to learn how we perceive food, physiologists first discovered the taste buds, that is, groups of sensitive cells that are responsible for detecting tasty-or sapid-molecules. In all mammals, taste is ensured by these receptors, distributed throughout the mouth, on the palate, epiglottis, pharynx, and especially the tongue. Our tongues have about nine thousand taste buds, in groups of fifty to one hundred, loaded with nerve endings. The number of taste buds seems to diminish with age, especially after the age of forty-five.9 Cla.s.sical works have been reexamined. The alchemists said this of taste and smell: corpora non agunt nisi soluta corpora non agunt nisi soluta (bodies are only capable of action in the divided state). They thought in macroscopic terms: nutmeg only has a flavor when reduced to a powder. In microscopic terms, alchemical law must be articulated in this way: a molecule is only sapid if it is soluble in water and has one or many receptors. If it is soluble in water, it is circulated through the saliva to the "nervous and sensitive tufts," as Alexandre Balthazar Laurent Grimod de la Reyniere called the taste buds. (bodies are only capable of action in the divided state). They thought in macroscopic terms: nutmeg only has a flavor when reduced to a powder. In microscopic terms, alchemical law must be articulated in this way: a molecule is only sapid if it is soluble in water and has one or many receptors. If it is soluble in water, it is circulated through the saliva to the "nervous and sensitive tufts," as Alexandre Balthazar Laurent Grimod de la Reyniere called the taste buds.10 Receptors are needed to induce some sensation, however: water-soluble molecules that lack receptors do not deliver taste. Receptors are needed to induce some sensation, however: water-soluble molecules that lack receptors do not deliver taste.

Petroleum jelly has no taste because its compounds do not dissolve in saliva. Apparently, sapidity results from the establishment of bonds between the sapid molecules and taste bud receptors. A molecule only has a taste if it is linked to the receptors present on the surface of the gustatory cells in the mouth. This connection seems to take place through a lock-and-key system. Because of complementary forms or electrical charges, the sapid molecule links to its specific receptor molecule and stimulates the nerves that relay the perception of a taste to the brain. The weakness of these links has the advantage of letting us sense different flavors at short intervals. One taste dispels another.

We can also understand why our forebears had so much difficulty distinguis.h.i.+ng tastes, odors, and proprioceptive sensations. These various perceptions are relayed along nerve pathways that merge upon entering the brain. The perception of a scent can alter our perception of a taste, for example. The flavor of a dish can depend on its temperature.

To study the perception of pure tastes, sensorial physiologists today use standardized experimental protocols and devices that gently blow air into the noses of the subjects being tested. If odors no longer pa.s.s through the retronasal openings (connecting the mouth and nose), the subjects perceive the true taste of the foods, the quintessential sapidity, as it were.

Despite the incontrovertible results recently obtained, the public and even certain distinguished scientists still believe that there are only four tastes. The error dates back to 1916, when the chemist Hans Henning proposed his "theory of the localization of receptors," according to which the mouth supposedly perceived only four tastes (salty, sour, sweet, bitter), through specialized taste buds confined to certain regions of the tongue. Sweet was supposedly perceived by taste buds located on the tip of the tongue, bitter by taste buds at the base of the tongue, salty by the front edges, and sour by the back edges.

Recent physiological a.n.a.lyses have revealed how wrong this theory is. First of all, even though the salt receptors are more numerous along the front edges of the tongue, they are present throughout the mouth and all over the tongue. Similarly, the sweet, sour, and bitter receptors are present throughout, though in varying proportions. Furthermore, licorice, for example, because of glycyrrhizic acid, is neither sweet, nor bitter, nor salty, nor sour. And the molecules acting as gustatory receptors seem very much more varied than once supposed, forming weak bonds with molecules sometimes very different from one another.

Recent studies have not called into question the reality of the salty taste, which is actually due only to sodium ions, or the sour taste, which is due to hydrogen ions, but they have demonstrated the vast and varied nature of the domain of taste and confirmed Brillat-Savarin's vision.11 Salt forms molecular structures with food proteins, structures that are stable in the cold but destroyed by heat. Salt having thus formed what chemists call a complex cannot stimulate the taste buds. That is why a given amount of salt by itself produces a salty taste, cold, and that is also why, given equal concentrations of salt, raw products seem less salty than warm, cooked products. Salt forms molecular structures with food proteins, structures that are stable in the cold but destroyed by heat. Salt having thus formed what chemists call a complex cannot stimulate the taste buds. That is why a given amount of salt by itself produces a salty taste, cold, and that is also why, given equal concentrations of salt, raw products seem less salty than warm, cooked products.

In addition, fat often does not seem salty, because it does not dissolve salt and contains little water, which does. On the other hand, it is good at dissolving many odorant molecules. It is primarily the fat in meat that gives it its characteristic flavor. Try the experiment of cooking a lean piece of pork with lamb fat. Say nothing to your dinner guests and ask them what they think they are eating.

Licorice, with its glycyrrhizic acid, is not the only substance with a taste that does not appear in the list sanctioned by ignorance. j.a.panese physiologists have demonstrated the need to add the taste umami as well. Umami is said to be a universal taste, although this is a complicated matter. The fact is that umami characterizes the taste of broths called das.h.i.+, made by infusing kombu (kelp) in hot water. During the infusion process, primarily two amino acids are released, glutamic acid and alanine, so that, strictly speaking, umami is the taste of the combination of these two products, not of glutamic acid, as has been claimed. So, are there four tastes, or five, or six? None of the above. Numerous molecules, the various amino acids or quinine (the prototypical bitter molecule), for instance, among many others, have unique tastes that cannot be reduced to a combination of other tastes.

Even sweet is more complex than we once imagined. The various modern sweeteners sweeten everything, but they do not all have the same sweet taste. As for the relations.h.i.+ps between sweet and bitter, they are astonis.h.i.+ng. Certain molecules, such as methylmannopyranoside, have both a sweet and bitter taste, or only sweet, or only bitter, depending on the individual. Why? We do not know, but recent scientific works provide glimpses of new phenomena.

I would like to propose a little detour (another one, my dear gastronomads) into two of these studies, one on sweet tastes, and one on strange molecules in the form of an L L that are simultaneously bitter and sweet. that are simultaneously bitter and sweet.

Recent Progress in the Chemistry of Sweeteners Since scientific studies of the gustatory receptors are difficult because these receptors have only a weak affinity for the sapid molecules, certain physiologists are a.n.a.lyzing gustatory phenomena indirectly by having subjects taste various sweet molecules, for example, every day for several months. In a laboratory in Ma.s.sy, near Paris, many hundreds of individuals tested twenty sapid molecules in this way, using the nasal air current device previously described.

Thus, in the early 1980s, the neurophysiologist Annick Faurion and her colleagues discovered that the threshold for detecting sucrose, that is, the smallest quant.i.ty of table sugar perceptible in a fixed quant.i.ty of water, varies from one individual to another. Likewise, the thresholds for perceiving various other sweeteners are specific to individuals. In other words, the quant.i.ty of sugar that we take in our coffee depends not only on the sensation we like to have but also on our own personal sensitivity to the sweetening molecule. Moreover, the sensitivity threshold depends on the sweetening molecules themselves. Some individuals are more sensitive to sucrose (table sugar), others to glucose (the sugar in honey or grapes).

What is fascinating, though not surprising, is that the detection thresholds evolve through "learning." Over the course of the trials, the thresholds decreased; that is to say, sensitivity increased. Furthermore, when the training for one molecule ended, that is, when the detection threshold ceased to vary, it continued for other molecules. What a stroke of luck! This kind of observation demonstrates that, if we want to, we can train ourselves to develop fine palates.

Finally, comparisons among various molecules in different concentrations revealed an additional complexity in the gustatory system. The sweet taste of a sweetening molecule depends on its concentration. That is an effect we must consider, looking toward the day when we reach the final stage of mastering the slightest variation in flavor in the dishes we prepare.

What relations.h.i.+p exists between a molecule's structure and its taste? The indirect studies done in Ma.s.sy and elsewhere have not answered this question, of interest to higher gastronomy. Yet if we understood these structure-activity relations.h.i.+ps, as scientists call them, we could synthesize molecules tailor-made to individual tastes!

Because of the huge market for synthetic sweeteners, this subject has been addressed with special attention to sweet molecules, and enticing prospects appeared when Murray Goodman and his colleagues at the University of San Diego tested subjects with peptidic sweeteners (peptides are small molecules formed from chains of only a few amino acids). As in many artificial sweeteners-aspartame, for example-these molecules contain two rings of atoms, only the first of which can bond to water molecules, linked by a short chain of atoms in the form of an elbow at a right angle. The rings are semicoplanar, and the complete molecule forms an L-shape.

By altering such molecules so that the two rings are no longer coplanar, the San Diego chemists first obtained molecules with no taste. Then, by placing one flexible molecular part between the rings, they created molecules in which the rings could turn in relations.h.i.+p to one another. The continuous movements of the molecules can actually make the rings turn incessantly and very rapidly, at a speed that varies according to the relative orientation of the rings.

The taste of these molecules is ... unpredictable. Some seem bitter at first, then sweet, whereas others are initially sweet, then bitter. This strange property might result from certain molecules being in a sweet configuration longer and bonding initially to the sweet receptors, while others, in a bitter configuration longer, bond more to the bitter receptors. When are we going to have the same "blinking" effect with other tastes?

We have not heard the final word in this gustatory adventure. As Brillat-Savarin sensed, tastes are astonis.h.i.+ngly complex. Even without considering the "flas.h.i.+ng light" tastes discussed above, studies seem to indicate that tastes inhabit a ten-dimensional s.p.a.ce. In other words, tastes seem to be infinite in number, and ten descriptors at least would be necessary to talk about them. We are falling far short of the mark with only sour, bitter, sweet, and salty.

Does Taste Lose Its Edge As One Eats?

Do we perceive the taste of a dish or a drink less well after consuming a great deal of it? This question deserves study, because Brillat-Savarin affirmed-with as much authority as good reason, I believe-that "the most delicious rarity loses its influence when its quant.i.ty is stingy."12 Yet what would be the interest in consuming a dish in abundance if the perception that we have of it and the pleasure that it provides us disappear after a few mouthfuls? Yet what would be the interest in consuming a dish in abundance if the perception that we have of it and the pleasure that it provides us disappear after a few mouthfuls?

Let me pose the question in concrete terms: does the taste of mustard disappear when we overuse this condiment? Do we lose our sensitivity to wine when we allow ourselves the time to taste it and to examine all the components of its bouquet? Or, on the contrary, does practice in the perception of flavor increase sensitivity through the phenomenon of training?

Let me clarify these ideas by stating first of all that the term "fatigue" can be used in several ways. The first is an alteration in the physiological state of the muscles, which takes place only in very rare cases when we eat tough or hard products. The second corresponds to a progressive incapacity of the nervous system to a.n.a.lyze the signals it receives. This is the mental fatigue brought on by psych.o.m.otor (for example, dactylography) or intellectual (the case of flight controllers) tasks. If we acknowledge that the exercise of gustatory or olfactory perception is a recognition of forms, like dactylography or flight control, we can a.s.sume that mental fatigue can also occur in the sensory evaluation of food products.

Third, we also call a waning of interest in what we are doing "fatigue," because the activity is monotonous or because we consider it too difficult. This form of fatigue should be called "la.s.situde" instead. Such fatigue does not seem to apply to gourmands. How can they get tired of good things?

Finally, fatigue can be the weakening of a sensation as a result of constant exposure to a stimulus. We no longer notice the odor of a stuffy room a few minutes after entering it. This phenomenon is an inevitable adaptation, but since it occurs as much at the beginning as at the end of the tasting process, it seems wrong to consider it a true instance of fatigue. Furthermore, it may be that an adaptation to stimuli increases the quality of perception. Wine tasters rinse their mouths with wine (thus adapting their palates) before beginning an evaluation session, to provide themselves with a point of reference, just as musicians tune their instruments together before a concert. This phenomenon is well known among taste physiologists, who have observed that the threshold of perception for sucrose (table sugar) in water is lower (one is more sensitive to it) when subjects rinse their mouths with a sucrose solution before the trials than when they do not rinse or rinse with plain water.

To learn definitively whether the taste sense is dulled or not, Francois Sauvageot and his colleagues at Dijon University did sensory evaluation tests on subjects in which the difficulty of the task proposed to any subject at a given time depended on the quality of the prior response. When subjects gave correct responses, the next tests they had to pa.s.s were more complicated. When they made mistakes, the next tests were easier. The trials lasted four to five hours, with a thirty-minute break midway through the session. On average, the results for tasting did not deteriorate over the course of the sessions. Taste was not dulled. Good news for gourmands, who, without knowing the results of these experiments, must have hoped for this outcome.

Taste and Colors It is sometimes said that the colors on a table are half the meal. No doubt that is true, in a sense: we do not expect the same kind of pleasure when entering a dining room glimmering with candles, crystal, and silverware as when we sit down to eat at a counter covered with an oilcloth in garish hues.

Do colors determine the flavor of a dish in the same way the temperature of a food alters its taste? It is hard to answer that question because oral pleasure can never be reduced to a single factor. Since gastronomy is precisely the art of combining pleasures, it would go very much against the grain to isolate out colors in order to examine their hedonic power.

So let us concentrate instead on the strange relations.h.i.+p that seems to exist between the color of a dish and the hunger it prompts. Intuitively, cooks strive to retain the fresh color of vegetables, a certain pinkness to meats, the white of fish. Pastry cooks have the time of their lives creating creams in tempting colors.

A cla.s.sic cookbook published in the 1960s by the French food critic Curnonsky introduced the prize-winning creations of pastry cooks who used methylene blue to color their cakes.13 Cooks rarely resort to such colorations, but they know that gray meat or yellowish leeks are not appealing. Cooks rarely resort to such colorations, but they know that gray meat or yellowish leeks are not appealing.

In his Grand dictionnaire de cuisine Grand dictionnaire de cuisine, Alexandre Dumas lists several "inoffensive" food colorings that can brighten dishes:

BLUE:indigo diluted in water YELLOW:gamboge or saffron GREEN:juice of spinach leaves or crushed green wheat, cooked over a flame, strained, and diluted in sugar water RED:cochineal and alum powder boiled in water CRIMSON:pollen from dried wild carrot flowers diluted in water or elderberry juice diluted in water PURPLE:cochineal and Prussian blue ORANGE:saffron and cochineal

Are these colorings really inoffensive? And, more important, are they enticing? The following anecdote demonstrates that Curnonsky hit the nail on the head when he remarked that "things are good when they have the flavor [and the color, let us add] of what they are." For a dinner that later became famous, the amphitryon had wanted all the dishes to be green, as well as all the objects on the table and in the dining room: tablecloth, napkins, place settings. The guests had a very hard time swallowing even a few mouthfuls, and some departed, leaving their host to clean up the little they had temporarily forced down. More recently, in taste trials, even competent judges have mistaken orange juice dyed blue for blueberry juice or even white wine, colored with flavorless pigments, for red. Let us not force the hand of nature but rather compensate when we degrade it. We can certainly give wilted vegetables their colors back, but why not eat fresh or perfectly cooked ones?