Note-by-note cooking will sound the death knell for the false theory of the four tastes. Once chefs and gourmets taste pure compounds, they will notice real differences that until now have been hidden from them by four simplistic and misleading terms: salty, sweet, acid, bitter. Words do sometimes lead us astray, it is true. A new vocabulary will have to be introduced.
The difficulty facing anyone who wishes to have a better understanding of taste is that gustatory perception is influenced to a very substantial degree by color, consistency, smell, and so on. When we eat, our perception of tastes is inevitably mixed with the perception of odors because odorant molecules released by chewing rise up into the nose. It is therefore possible to isolate tastes only by closing off the retronasal channel. You could do this, of course, by holding your nose while eating, but a better way would be to use a small aquarium pump to blow air through a tube inserted in one nostril while pinching the other; alternatively, you could make a small mask out of modeling clay and divide the stream of air coming from the pump into two equal streams passing into the nostrils at the same time. The air from the pump blocks the odorant molecules from reaching the nose, so you can perceive the taste of pure compounds.
MISDIRECTION AND MISPERCEPTION
The gourmet who is serious about exploring the world of tastes will also have to dissolve sapid compounds. Why? Because otherwise he will be fooled by the consistency of the foods he eats (as you can see for yourself by comparing the taste of sea salt, table salt, and salt that has been finely ground). Color will have to be disguised as well (sensory analysis is often done by putting subjects in rooms lit with red light, but you can also simply close your eyes). Having taken these precautions regarding smell, consistency, and sight, begin by tasting whatever happens to be in your pantry: wine, chocolate, the oil in which sardines are packed, Roquefort—you name it. Just as novice oenophiles must learn to taste wines, aspiring gourmets will have to be taught to recognize the different tastes of the foods they eat, starting with traditional dishes and moving on to pure sapid compounds and artificial flavoring substances. Keep in mind that compounds can be both sapid and odorant. It is true that salt and sugar have no smell when they are pure, but what about the ethanol in brandies? It has a smell, quite obviously, but it also has a taste.
Moreover, the taste depends on its concentration when it is mixed with water. This is a phenomenon that sensory physiologists are well familiar with: even the taste of salt and sugar varies according to their concentration; indeed, at very low concentrations in water, salt can actually taste sweet.
Note, too, that if the theory of the four tastes is false, the familiar map of taste-receptor areas on the tongue is no less mistaken, no matter how many times it may have been reproduced in monographs, textbooks, and works of popular science. It is a mystery that this map should still have any credibility at all. One has only to put a few drops of sapid solution on different parts of the tongues of different people to see that the map changes from person to person. It is customarily said, for example, that the tip of the tongue recognizes sweetness—a doubtful notion to begin with since there are several kinds of sweetness. As it happens, many people sense sweetness less on the tip of the tongue than on other parts of the organ. (Personally, I register a variety of sour sensations there.) When participants in a seminar held in Paris a few years ago were invited to stick their tongues in a glass of sweetened water, only 40 percent of them sensed a sweet taste in the tip of the tongue.
How do such misconceptions gain currency? The answer seems to be that human beings are susceptible to arguments from authority: we willingly adopt the ideas of acknowledged experts, no matter how far-fetched they may be. We are, after all, ourselves primates, a group of animals in which certain dominant individuals are able to persuade the other members of the group to do more than they could be made to do by force alone. Nevertheless it is also true that in matters of taste it is what each of us likes personally that we consider to be good: if we don’t like a dish, we can’t imagine it’s worth eating—even if we know that a billion people are wild about it; conversely, if we like something, there’s no point arguing about it, unless of course we want to argue with friends for the sake of cultivating a spirit of open discussion and strengthening social ties. This last point seems to me essential. When we debate the meaning of existence over a meal in the corner bistro, we do so as part of a group. Being part of a group is the crucial fact of life for members of a social species.
But I digress. Anyone who wishes to construct note-by-note dishes will have to acquaint himself or herself with the tastes of compounds in order, as I have already said more than once, to learn to say new words in a new language and then to make new sentences. No doubt this is why some cooks will resist note-by-note cooking. Understandably, they do not relish the thought of being dispossessed of everything they have learned until now—of being stripped naked, as it were, both intellectually and professionally. But this will be true only for cooks who are timid or lazy; for the others—the artists, the innovators, the brave and industrious ones—the prospect of discovering a new world will be experienced as an immense thrill and welcomed as an incomparable opportunity.
THE IMPOSSIBLE DESCRIPTION OF UNKNOWN TASTES
Earlier we saw that although shapes can be readily enough described, consistencies are harder to imagine when we have not encountered them before. What about tastes? Suppose you had never tasted sweetness. We do, of course, have certain points of reference for naturally occurring compounds in the vegetable and animal kingdoms: the tastes of meats, fruits, and vegetables that contain these compounds in significant concentrations. Anyone who has tasted sugar cane or honey can easily imagine the taste of sucrose.
Even so, the ability to construct note-by-note dishes requires a period of apprenticeship. As in the case of consistencies, the wisest course will be to acquaint ourselves with the taste of pure sapid compounds before sampling pairs of such compounds, triplets, and so on. By itself, however, tasting isn’t enough, for being human also means sharing. This is why we must also devise a new vocabulary of tastes that goes beyond the worn-out mantra “salty, sweet, sour, bitter,” which for many years now has been refuted both by personal experience and by sensory physiology. Consider, for example, sodium bicarbonate, which is used in cooking chiefly to soften dry vegetables and to keep green vegetables green. It has a somewhat soapy taste, but not quite soapy either; it is sweetish, but not really sweet; slightly salty, but at the same time something else. How are we to describe it? Obviously we could speak of “bicarbonate of soda taste,” but this would force us to introduce as many such terms as there are compounds! For the glycyrrhizic acid of licorice, we would then have to say “glycyrrhizic acid taste”; for glucose, “glucose taste”; for aspartame, “aspartame taste”; for tyrosine, “tyrosine taste”; and so on without end.
This difficulty is compounded by the fact that human beings perceive different tastes differently. An excellent example is monosodium glutamate, much used by cooks in parts of East Asia and by certain sectors of the food industry in Western countries. It is derived from glutamic acid, which, together with other amino acids, becomes linked in chains of various lengths to form proteins, and in particular the very proteins on which the functioning of the human body depends. Like all acids, it loses a hydrogen atom when it is dissolved in water, forming a glutamate ion. If this glutamate ion is combined with sodium ions (sodium atoms that have lost an electron), one obtains monosodium glutamate in the form of small, white, needlelike crystals.
When a fairly large number of people chosen at random taste monosodium glutamate, they fall into three groups: some subjects perceive a salty taste, some a sweet (or at least a very mild) taste, and still others an assertive taste of chicken broth. These sensations seem to correspond to individual genetic differences. Moreover, the phenomenon is almost surely not restricted to the perception of tastes. After all, it is not because we call a certain color blue that all of us perceive it in the same fashion. This suggests that it will be possible to find a common gustatory language if we start from a shared set of conventions.
SAPID COMPOUNDS
What is there to be said, then, about sapid compounds? To be honest, we know scarcely anything at all about them. It is true that I shall go on in a moment to examine a considerable variety of sapid compounds about which a great deal is known. But much more remains yet to be discovered before we can claim to have a proper understanding of this vast and so far largely uncharted world.
Let us begin this time by adopting a biological point of view. Why do we perceive tastes? The question is poorly put because yet again it seems to suggest that biological evolution has a purpose. Few people really believe that human beings were endowed with the faculty of perceiving tastes, which I have proposed to call “sapiction,” so that they could take pleasure from eating.
No less than our ancestors, we are animals, and if we are alive today it is only because our ancestors succeeded in reproducing themselves. And if they were able to reproduce, it is because they managed to reach sexual maturity, which means they found a way to feed themselves. And if they were able to feed themselves, it is because their sapictive system allowed them to recognize foods, which is to say edible things from which they could absorb nourishment and energy. As the anthropologist Claude Marcel Hladik has emphasized, nonhuman primates (the “apes”) coevolved with plants that produced sweet fruits. Our ancestors benefited from ingesting the sugars of these fruits and in dispersing their seeds and pits caused sweet fruits to be widely propagated. The consumption of toxic plants, by contrast, was discouraged by the presence of various compounds, typically bitter in taste, with the result that their propagation depended on other mechanisms of dispersal. Still today, human beings commonly consider bitterness to signal danger. But plainly this is not always true. Beer is perfectly safe to drink, even though the alpha-humulene contributed by hops makes it bitter.
It should be clear that opposing sweetness to bitterness serves no real purpose. The only things that matter are the specific proteins, known as receptors, on the surface of the papillary cells in the mouth and on the tongue that register specific tastes. When we eat a food, it releases various compounds; some of these compounds dissolve in saliva, as we have seen, and some of those that dissolve can bind with a receptor, producing a sapid sensation. Although water solubility is a necessary condition of our perceiving taste, it is not a sufficient one: some compounds that dissolve in saliva have no taste, quite simply because neither the mouth nor the tongue contains the receptors needed to detect them.
The word detect is really a bit too strong, for it is a verb of action. Taste receptors consist of inert strings of protein that are more or less compactly folded up on the surface of the papillary cells. Owing to the random motion of molecules in solution, one such molecule may pass in the vicinity of a receptor. A sapictive sensation is registered when a sort of complementarity between the molecule and the receptor allows a bond to be established. Think of the receptor as a string on which north and south magnetic poles are located at various places: if the compound that comes near to a receptor is complementary, then the molecule–receptor connection is made; if not, nothing happens. In those cases where a compound binds with a receptor, a series of molecular transformations causes an electrical signal to be transmitted from the cell bearing the receptor to the brain. There, in the brain, the signal is interpreted.
A compound may therefore be said to be sapid if it binds to a receptor. But a taste can also appear if two small molecules, neither of which is capable by itself of stimulating a sapictive sensation, succeed in binding to two parts of the same receptor. There may be any number of other possible configurations as well. As I say, the world of sensory physiology is still only very incompletely understood. Most of us would agree, I think, that enlightened food lovers should help to make the case for public funding of further research on this fundamental aspect of human experience. For the time being, however, let’s make do with the knowledge we have and take a quick look at some of the sapid compounds that we already understand fairly well, organizing them into a number of general categories for the sake of convenience.
MINERAL SALTS
The term mineral here denotes compounds that are not organic. Organic compounds are so called because they were found first in living organisms. The term is unfortunate, however, for organic compounds are now known to exist in everything and everywhere, even in interstellar space. Chemists used to suppose, following the Bible and the Quran, that the world is divided into two separate kingdoms, the living and the inanimate. The inanimate (or mineral) kingdom could be explored, and it was. In the course of examining various minerals, especially ores, chemists noticed that heating some of them produced acids and bases (or alkalis). The calcination of carbonates, for example, brings about the formation of a caustic substance, quicklime, which in water becomes slaked lime, an alkali with a mild taste. (But don’t dare ingest it in too concentrated a form!) Similarly, macerating wood ashes in water yields a caustic aqueous solution known as potassium hydroxide (caustic potash or lye).
It was soon observed that acids react with bases and form less corrosive substances, called mineral salts. Thus hydrochloric acid reacts with caustic soda (sodium hydroxide) to produce sodium chloride—which is nothing other than table salt. In reaction with potash, the same hydrochloric acid forms another mineral salt, potassium chloride. Starting from mineral substances, in other words, we obtain a class of substances that are neither acids nor bases.
In the early days of modern chemistry, these substances seemed very different from the organic compounds associated with living organisms. It was gradually discovered that the molecules of these compounds are typically composed of carbon, hydrogen, oxygen, and nitrogen atoms, sometimes in the company of sulfur and a few other elements. It came as a complete shock, then, a seismic upheaval, when the German chemist Friedrich Wöhler (1800–1882) discovered that heating a mineral substance could produce an organic compound. The barrier between the living and inanimate worlds suddenly collapsed—a terrible blow to the doctrine known as vitalism, according to which the living world contained something more than the inanimate world (a divine spark, as it was usually conceived). Now that biologists are able to construct viruses from scratch, synthesized compound by synthesized compound, only the ignorant can go on being vitalists—unless, of course, vitalism today is not a matter of ignorance, but of faith. In the latter case, not even the long-anticipated synthesis of a living cell (now an accomplished fact), molecule by molecule, will be enough to do away with vitalism, which will have taken refuge in objects other than physical bodies, substances, minerals, and atoms.
Let us come back, then, to more down-to-earth questions. Where are mineral salts found? In water, to begin with. On the label of every bottle of mineral water, there appears a list of ingredients: chloride, sodium, calcium, phosphate, hydrogen carbonate, nitrate, magnesium, fluoride. These ions are what give water its taste. Evidently our teachers in school were not telling the truth when they told us that water has no taste, for it is well known that no two mineral waters taste the same. Their taste depends on the proportion of mineral salts they contain.
How can the salts be separated from the water? Evaporating the water is one way, though not a costless one (assuming you use heat) or a very entertaining one (waiting for the water to boil off). The ions will eventually end up being deposited at the bottom of the pan, but in only very small amounts: the residue is seldom as much as a gram per liter of water; typically, it is on the order of 0.1 gram per liter. Another, more efficient method is to use one of several modern filtration systems, which operate on the same principle as the removable filter found in the water-filtration pitchers sold today in grocery stores. The recovered dry residue will in any case consist of a mixture of calcium, sodium, fluoride, carbonate, and other ions, and, as a practical matter, you won’t be able to taste any of them individually.
Indeed, experiencing the particular taste of an ion is impossible in principle, for ions are either positive or negative. An ion is an atom or a group of atoms that has lost or gained electrons, becoming a very powerful sort of magnet in the process (electromagnetic rather than magnetic, however). This means that cooks will never succeed in isolating ions of a single kind, unmixed with ions having an opposite electrical charge. In sodium chloride (table salt), for example, whether it is rock salt or sea salt, there will always be as many chloride ions as sodium ions; in potassium nitrate (known also as saltpeter, used in curing meats), there will always be as many potassium ions as nitrate ions, which are composed of one nitrogen atom and three oxygen atoms. The pure taste of an individual ion, as opposed to the taste of mixtures of ions, will therefore forever remain beyond our grasp (unless perhaps in the case of organic acids, but that’s another story). Even so, let’s not give up quite yet.
It may yet be possible to have at least some idea of what ions taste like. Get hold of some mineral salts (they’re ridiculously cheap, sold by the ton), dissolve them in water in low concentrations, and taste each solution separately; then mix them together, taking care to ensure that the overall concentration in these “cocktails” does not exceed the levels typically found in bottled mineral water—and that none of the ions is poisonous.
It is well known, for example, that there are ignorant (perhaps criminally ignorant) winemakers who treat their casks with volcanic sulfur. Any chemist can tell you that such “native” sulfur is liable to be contaminated by arsenic, an element that when burned produces arsenic oxide (a substance that used to be reserved for mothers-in-law). It is well known, too, that the Romans sweetened their wines with lead salts, especially lead acetate, a water-soluble salt. Some historians now wonder whether this practice may not ultimately have been responsible for the fall of the empire (lead is extremely toxic and would have poisoned the elites who drank such wines). Copper is scarcely a more prudent choice. You should think twice about spraying your garden with copper sulfate (following the example of winegrowers in France and elsewhere, who belatedly stopped spraying their vineyards with it after years of intensive treatment). We will do better, at least starting out, to limit ourselves to the ions found in mineral water. The problem is that although elements such as aluminum, scandium, titanium, chromium, vanadium, cobalt, and zinc do figure among the essential trace elements (oligoelements) studied by nutritionists, they occur in food only in very small quantities. Even talking about grams is out of the question! Selenium, for example, is found in fish in a proportion of 30 micrograms (a microgram is a millionth of a gram) per 100 grams of flesh and in meat in a proportion of 6 to 10 micrograms per 100 grams. An observed proportion of 55 micrograms per liter in the blood is sufficient to establish the presence of cardiovascular risk.
Again, as a practical matter, what does a microgram mean? A milligram? A gram? Georges-Auguste Escoffier’s Le Guide culinaire (1903), venerated in some quarters still today, courted ridicule by instructing cooks to season two eggs with 32 centigrams of salt, or 0.32 gram—an astonishing degree of precision at a time when kitchen scales measured to the gram, at best. One imagines that Escoffier (or perhaps one of his coauthors, Philéas Gilbert or Émile Fetu) obtained this value by dividing some measurable quantity of salt by the number of eggs called for in a recipe.
Assuming the number to be six, rather than two, yields a quantity of 1 gram, just about. But dividing 1 by 3 yields 0.333333 ad infinitum, not 0.32. To specify an exact number of centigrams in this case implies, altogether falsely, that gourmets are able to tell the difference between 0.3 and 0.4 grams of salt. Escoffier should have said instead: “Season in a proportion of roughly one-third of a gram of salt per egg.” That would have been more in keeping with customary practice. The moral of the tale? Undue precision is not only useless, it’s absurd!
And how much is a gram, really? Using a precisely calibrated scale to weigh the contents of a tablespoon of salt or sugar, you will usually get values between 5 and 10 cubic centimeters (a cubic centimeter is the volume of a cube each of whose sides measures one centimeter). The contents of a teaspoon are generally reckoned to be between 2.5 and 3.5 cubic centimeters—a figure that reflects not only minor variations in the actual size of different teaspoons, but also in the levels to which the spoons are filled. I had the idea once of pouring granulated sugar into the same teaspoon four times in succession and weighing the result. The values I got were 3.8985 grams, 4.1201 grams, 3.5644 grams, and 3.8892 grams. In other words, any given teaspoon contained about four grams of granulated sugar, but the exact value varied considerably from one teaspoon to another.
The time has now come to exchange theory for practice. Probably not many have actually tasted mineral salts. I have. Jacques Decoret in Vichy has experimented with salts recovered from the spring waters of his native region, which makes him the first chef I know of to use mineral salts in his cooking. The chefs most likely to follow him are ones with close ties to the world of winemaking, where aluminum salts are used when the fermentation process is in danger of being arrested because there are no more nitrogen compounds left for the yeast to absorb. The principal products authorized for winemaking in Europe are ammonium sulfate and ammonium phosphate, with a maximum approved dose of 0.3 grams per liter; ammonium sulfide and ammonium hydrogen sulfide are also permitted, though not in a proportion exceeding 0.2 grams per liter. These substances can’t help but change the taste of wine!
Salts are also authorized as additives in wine production, especially for purposes of preservation. A moment ago I mentioned the practice of sulfurizing wine barrels. This used to be done by burning sulfur to form sulfur dioxide, a substance that is liked neither by microorganisms (which are killed by it) nor by human beings (who are apt to get terrible headaches from it). Sulfides (E221–228) and sulfurous anhydride (another name for sulfur dioxide, E220) need to administered with caution. Among food preservatives, saltpeter has long been used to lengthen the shelf life of hard sausages and hams. Today the list of authorized additives includes both nitrates and sodium and potassium nitrites (E249–252), as well as boric acid (E284) and sodium tetra-borate (borax, E285), which are to be used sparingly. In this connection (recalling yet again the Romans’ habit of sweetening wines with lead salts), one shouldn’t suppose that what tastes good is always good for one’s health. Nor should the mostly unproblematic use of such compounds as preservatives lead anyone to suppose that they can be used in cooking without formal instruction. Chefs must be taught how to handle such products safely, just as they had to be trained in the proper use of liquid nitrogen in molecular cooking—or, for that matter, in the proper use of knives. All these things pose risks that must be minimized as far as possible.
ORGANIC AND MINERAL ACIDS
Let’s move on to acids, only this time starting with acidifiers, a well-tested class of derivative substances that appear in the list of approved food additives. These compounds—citric, acetic, tartaric, phosphoric, ascorbic, lactic, malic, and succinic acids, among others—enhance the taste of foods and beverages. Like their sodium, potassium, and calcium salts, they lower pH (a measure of acidity, as noted earlier, ranging from 0, for the most powerful acids, to 14, for the strongest bases).
Chemists know very well that acids are not interchangeable and that acidity is not the only thing that determines their taste (contrary to what the false theory of the four tastes would seem to suggest). Not only do they have different tastes, but the sensation of acidity is not equally long lasting in every case. Chemists also know that the addition of an acid makes it possible to sharpen or soften the perception of odorant compounds. This is why beverage manufacturers delight in exploiting the contrast between sweetness and tanginess (due mostly to the acidity of phosphoric acid)—a trick they picked up from traditional cooking. In France, cooks have long used gastriques, sweet-and-sour sauces that typically combine vinegar and sugar; they have also long been accustomed to add a touch of citrus juice to veal stews just before serving or a pinch of sugar to wine sauces or a dash of dry white wine to sauces for fish.
Then there is the class of acids proper. Among mineral acids, I mentioned hydrochloric acid (E507) earlier, but there are others: phosphoric acid (E338), sulfuric acid (E513), and so on. Their very names frighten the culinary world, but in low concentrations they are only mildly acidic and present no risk. To put matters in perspective, recall that raspberries are very acidic (they can have a pH as low as 2), whereas diluted hydrochloric acid can have a far higher pH (and therefore far lower acidity). Among organic acids, acetic acid (E260) is one of the best known because it is a product of alcoholic fermentation. It is the principal acid in vinegar, for example, in which it is produced by Mycoderma aceti, a microorganism that transforms the ethanol obtained from the fermentation of sugars into acetic acid. In its pure form, acetic acid is called glacial ethanoic acid—a transparent, colorless liquid with an unpleasantly pungent odor that dissolves in water in all proportions. Is it something we should be afraid of? No, because anyone who sniffs glacial ethanoic acid will at once realize that it is not to be swallowed, and because once dissolved in water it turns into something that is both harmless and very familiar—white vinegar! Acetic acid is officially approved today for use as a preservative. This will come as no surprise to cooks, who have long been in the habit of preserving little gherkins (known in France as cornichons) in white vinegar.
Lactic acid (E270) has an equally ancient pedigree. Produced by bacterial fermentation of lactose, a sugar found in milk, lactic acid is what gives yogurt and some cheeses their slightly sour taste. It is also found in hard sausages, sauerkraut, pickled cucumbers, turnips, green olives, and so on. In its pure state it is a viscous, nonvolatile liquid. It is authorized both in this form and in that of its sodium salt for certain preparations of black olives as well as in the manufacture of certain new processed cheese products.
Citric acid (E330) is the principal acid in lemon juice. In its pure form, it is a white powder. Many chemists fondly remember making “artificial” lemonades as children by mixing pure citric acid with sodium bicarbonate. Combine the two powders in roughly equal proportions (I myself recommend putting more citric acid than bicarbonate), add water, and voilà, you’ve got a sparkling and delightfully lemony soda—sweetened with a dash of sugar if you like!
Tartaric acid (E334) is famous for having made Louis Pasteur’s reputation. The marvelous advances in microbiology due to this son of a winegrower (whose vineyard in the Jura is the property of the French Academy of Sciences today) have caused us to forget that he made an extraordinary discovery while studying tartaric acid in grapes. Pasteur was the first to realize that there exist pairs of compounds whose properties differ even though their atoms are identical. Just as a right hand is the image of a left hand in a mirror, so the atoms of these pairs of compounds are ordered in such a way that they form molecules having mirror-image forms; and just as a left hand won’t fit into a right-hand glove, so a “left-hand” molecule cannot bind with a “right-hand” receptor. Ignorance of this phenomenon was responsible for the catastrophe of thalidomide, a drug given to pregnant women that caused missing or malformed limbs in their children. The organization of atoms in space is important for odorant molecules (we will see in chapter 4 that limonene, depending on whether it is a right-hand or left-hand molecule, has a smell of lemon or of orange), but also for some sapid molecules as well.
The tartaric acid found in grapes occurs in a form denoted by the symbol L(+)—it would take too long and be of too little interest for our purposes here to explain why—and it is in this form that it is used to acidify liquids and wines. Oenologists and winemakers habitually use tartaric acid in alcoholic fermentation, though getting the proportions right takes practice: if it is added to a wine before the process of cold stabilization (which causes potassium tartrate to crystallize) is initiated, predicting the degree of acidification is difficult. The legal limit is 1.5 grams of tartaric acid per liter for musts and 2.5 grams per liter for wines—roughly a teaspoon per liter of liquid, in other words. Its taste? I leave it to you to judge. Personally, I find it elegantly acidic, unlike acetic acid, which has a rather sharper edge. It would be a welcome thing, by the way, if, in addition to salt and pepper shakers, we were to put a tartrate shaker on our dining room tables. But what, I wonder, should we call a shaker that contains lactic acid?
Perhaps we should stop here before we find ourselves too far afield. Once again, a whole volume could be devoted to acids. We haven’t yet even touched on malic acid (from the Latin word for apple, malum), ascorbic acid, vitamin C, or, indeed, many others. There’s an acid for every taste!
AMINO ACIDS AND THEIR DERIVATIVES
Alongside the particular acids I have already mentioned, there is another set of organic acids having quite different tastes: the amino acids. These compounds are molecules that contain both a group of atoms known as a carboxyl (—COOH) group, present in carboxylic acids (consisting of one carbon atom, two oxygen atoms, and one hydrogen atom) and an amino (—NH2) group (consisting of one nitrogen atom and two hydrogen atoms). The arrangement indicated by the general formula is never actually encountered in the real world because, depending on the acidity of a particular environment, the carboxyl group is liable to lose its hydrogen atom or the amino group is liable to gain a hydrogen atom. The molecular details are of little importance for someone just beginning to explore note-by-note cooking without any training in the marvelous science of chemistry. Novices will do well simply to keep in mind that what is written in many textbooks on food science and technology is false—namely, that amino acids are either sweet or bitter.
First, where do amino acids come from? In the human body, they are the links in the molecular chains that form proteins. Proteins are of two kinds: some are what we are made of (the collagen of collagenous tissue, for example, found in muscles and tendons); others, known as enzymes, perform specialized tasks (proteases, for example, serve to cut up other proteins into small pieces, which are none other than amino acids). And so, yes, we are literally full of amino acids. They have various functions in the human body, just as they do in fruits, vegetables, meats, and fish. Proteins, which occur in all living things, are made up of twenty-one amino acids that bear charming names: glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, aspartic acid, glutamic acid, lysine, arginine, histidine, phenylalanine, tyrosine, tryptophan, proline, hydroxyproline, asparagine, glutamine. What do they taste like? Here again I would have a very hard time describing such sensations in words, but you can try tasting these substances for yourself (health food stores and even supermarkets now sell them). Earlier I mentioned monosodium glutamate, the sodium salt of glutamic acid, which is an amino acid.
All the compounds I discuss in this book can be used to make foods, of course, but there is no reason why they themselves should not be cooked as well. They can be pan fried or grilled or roasted or fermented or braised. The slow cooking of proteins in water, for example, produces a reaction known as hydrolysis, which cuts the proteins up into amino acids as well as fragments called peptides. It is for this reason that gelatin, if it is cooked long enough, no longer sets the cooking liquid in the form of a gel but instead strengthens and intensifies the liquid’s flavor. It is for this reason, too, that meats that have been slowly braised acquire a marvelous flavor that makes you want to keep on eating. And it is also for this reason that the fish sauces of Southeast Asian cuisines, not unlike the garum of the ancient Romans, impart so much flavor: monosodium glutamate is neither a great culinary novelty nor a Japanese invention; cooks in many countries have been making preparations of this type since antiquity, widely imitated thereafter.
Allow me, if you will, to anticipate somewhat the discussion of sugars that follows and mention a class of reactions named after the French chemist Louis Camille Maillard (1878–1936). Maillard discovered that amino acids react with so-called reducing sugars, such as glucose, with the result that, following an initial condensation reaction (in which an amino acid molecule binds with a sugar molecule and hydrogen and oxygen are eliminated in the form of water molecules), rearrangements of various atoms produce a great many odorant, sapid, and coloring compounds. Although these Maillard reactions are not solely responsible for the taste of bread crusts and roasted meats, they do decisively contribute to it. Amino acids can nevertheless react and be transformed even if they are heated in water without sugar. Cooking cysteine, for example, releases a gas called hydrogen sulfide. In large quantities, this gas is both nauseating (it has a smell of rotten eggs) and toxic; indeed, it is all the more dangerous as the first sign of intoxication is masked by the fact that, because hydrogen sulfide deadens the sense of smell, its presence can no longer be detected. In lesser amounts, however, it imparts an agreeable taste of cooked egg.
These few examples will suffice, I trust, to show that the cooking of amino acids may form the basis of a theory of new compounds, just as the cooking of sugars to make caramels inspired research on the chemistry of sugars more than a century ago—which leads directly to my next topic.
SUGARS
Normally, a lengthy introduction to this sizeable group of compounds would be required, distinguishing between carbohydrates, saccharides, monosaccharides, and so on. But it would serve no very useful purpose in this case, and I propose to dispense with it altogether, except for a few preliminary words regarding the term carbon hydrate. A little historical background is needed to understand why chemists consider it to be a misnomer. Modern chemistry began with elemental analysis: for any given pure compound, chemists sought to determine the quantity of carbon, hydrogen, oxygen, and other elements it contained. In the case of sucrose, for example, they found twelve parts carbon for twenty-four of hydrogen and twelve of oxygen. Having detected twice as much hydrogen as oxygen, as in the case of water, they concluded that sucrose contains water in addition to carbon—more precisely, that it contains one part water for every part carbon. This should not seem so surprising, really, for chemistry was still in thrall to the ancient doctrine of the four elements, according to which all matter is made up of earth, fire, air, and water. In short, imagining that sucrose consists of water and carbon, chemists considered sucrose to be a carbon hydrate, just like the other sugars, which, as it happens, contain the same proportion of one part carbon for one part oxygen and two parts hydrogen.
Elemental analysis nevertheless said nothing about the structure of molecules, and chemists soon came to realize that they were dealing instead with a family of so-called polyhydroxylated compounds, in which several carbon atoms bear a hydroxyl group consisting of an oxygen atom joined to a hydrogen atom. I won’t go into the details, which chemists find fascinating, but which most note-by-note cooks and general readers will not need to know. It is enough to say that there exist on the one hand simple sugars and on the other more elaborate sugars formed by linking simple sugars together to form chains, just as proteins are formed by creating chains of amino acids. There is, however, one essential difference: whereas proteins are linked in linear chains only, sugars may be linked in both linear and branching chains.
THE SIMPLEST SUGARS
The simplest sugar is glycerol, also known as glycerine (E422). It is used in making wines and has a mild taste. It is still seldom used in cooking, but that may change before long.
Glucose is only slightly more complicated. Present in most vegetables and abundant in carrots, onions, fruits, and honey, it serves, as we saw earlier, as a source of fuel for the human body. Glucose is not officially classified as an additive, though it can be used as one. In its pure state, it is not a syrup, as pastry chefs (who buy it in this form) are inclined to believe, but a white powder with a singular taste. Its appeal can readily be seen by performing a simple experiment: add glucose to any classic sauce, and you will see that it enhances the taste in a most remarkable way. What is more, it is very easy to prepare: all you have to do is hydrolyze a modified starch (as the food industry has done for many years now in manufacturing the glucose syrup generally used in pastry making).
Fructose, like glucose, is found in carrots, onions, and other vegetables, as well as in fruits—whence its name. Honey is more than 40 percent fructose. Much sweeter than glucose and even than sucrose, it has a wide range of uses in the food industry. Indirectly, however, it is responsible for the disappearance of a part of the honey bee population in the United States, which raises the question in some people’s minds whether glucose poses a danger to human health. Again, I must ask the reader’s indulgence, for the opportunity to take up arms once more against the merchants of fear whom I assailed earlier is irresistible.
The facts of the matter are as follows. Beekeepers, having learned that bees were attracted to fructose syrup that had been spilled in food-processing plants, naturally thought of using this inexpensive product to feed their hives. What they didn’t realize (because no one realized it at the time) was that under sunlight fructose is gradually transformed into a compound called hydroxymethylfurfural, which, despite its delightful caramel odor, is poisonous to bees. But hydroxymethylfurfural does not pose a comparable risk to human beings, for the simple reason that humans are not bees. What’s more, anyone who believes that hydroxymethylfurfural is to be avoided should also stop eating caramel—and indeed any dish in which liquids containing fructose have been heated or in which fruits and vegetables have been cooked. The idea is obviously absurd. This is why I feel an obligation, not only in my writings but also in my teaching and lecturing, to combat fears that have no basis in sound research and reasoned argument. The problem is not that we have too much chemistry, but that we do not have enough of it. Precisely because chemistry is a science, it permits us to distinguish between those things that pose dangers, when they are proved to exist, and those things that do not.
Let’s move on now to sucrose—ordinary table sugar. This time it is clearly not necessary to make any introductions. I shall limit myself to saying that the sucrose molecule is a chain of glucose and fructose units, and that although sucrose does not play a role in Maillard reactions (about which I shall have more to say in a moment), it can be used to make caramel. This is a remarkable phenomenon, which can be extended to include other simple sugars. Heating table sugar to obtain caramel is not merely a splendid example of note-by-note cooking, but also an archetypal example because it shows that compounds do not need to be used only in their raw state; they can be cooked as well. In the case of caramel, especially if a drop of lemon juice or vinegar has been added, the sucrose molecules disassociate, splitting into glucose and fructose; the fructose molecules then react, forming fructose dianhydrides, reactive compounds that bond in turn with neighboring sugar molecules. By applying the same technique to glucose and fructose it is possible to obtain new kinds of caramel, which I have proposed naming “péligots” in honor of the French chemist Eugène Melchior Péligot, whom we have already met, a pioneer in the study of caramelization. More about these later.
There are a great many other simple sugars in addition to glucose and fructose, and it would be a wearisome business to go through them all, one by one. Let me limit myself therefore to mentioning just a few: mannose, rhamnose, galacturonic acid, guluronic acid, glucuronic acid, sorbitol, lactitol, maltitol, maltose, mannitol, xylitol, agarose, galactose. Some of them are today considered to be additives, others not, but the reasons why are of no concern to us here.
COMPLEX SUGARS
Simple sugars such as glucose, galactose, and fructose are technically known as monosaccharides. Sucrose, a disaccharide formed by linking two monosaccharides together, is somewhat more complex. Linking three monosaccharides together gives you trisaccharides, linking four together gives you tetrasaccharides, linking five together gives you pentasaccharides, and so on. Onions contain fructooligosaccharides, in which one glucose molecule is linked to several fructose molecules. Inulin, found in chicory, is also an oligosaccharide.
Once the number of monosaccharide units exceeds ten, we arrive at the complex sugars, polysaccharides. Although polysaccharides generally are tasteless, they are useful in creating consistency, as we saw not only in the case of cellulose, but also of amylose and amylopectin, found in starches; of chitosan, produced from chitin; of various compounds extracted from algae; and of gums, to name only a few. As I say, these compounds typically have no taste except when small amounts of sugar are released in the mouth. Salivary amylases, for example, are proteins that function as enzymes, cutting up long chains of amylose and amylopectin in flour, with the result that after a few seconds a sweet taste appears—enough of one, at any rate, to allow an inventive cook to achieve novel effects.
ALCOHOLS AND POLYOLS
ALCOHOLS
The best-known alcohol is ethanol, preponderant in wines, beers, ciders, and brandies. It was the first alcohol to be distilled in the early medieval period—a discovery that bought about an upheaval in chemistry, for until then it was believed that all matter was made of four primary substances (water, fire, earth, and air). Distillation had succeeded in creating a fifth substance, a quinte essence.
Ethanol is nevertheless not the simplest alcohol from the point of view of its molecular structure. In organic chemistry, an alcohol defined is a compound whose molecules bear a hydroxyl group (in which one oxygen atom is bound to a hydrogen atom). The simplest alcohol—having a single carbon atom, a functional group (in this case the hydroxyl group—OH), and two hydrogen atoms for good measure (satisfying the requirement that each carbon atom must be bound to four other atoms)—is methanol, also known as wood alcohol. It is prepared by prolyzing wood, which is to say that the wood is heated in an airtight stove, producing gases that are highly flammable because they are rich in methanol. I should hasten to add that methanol is very toxic (indeed, in sufficient quantities it makes people go mad and blind), and government agencies are therefore justified in strictly regulating the production and sale of white alcohols, which give off methanol during the distillation process. The small quantity of methanol that survives this process is at least partly responsible for hangovers. Drinking too much white alcohol causes the jaws to tighten and become clenched—the first sign of methanol poisoning. This may well be the origin of the French expression for a hangover, gueule de bois (literally “wooden mouth”), though of course no one can say for sure.
Adding a second carbon atom gives us ethanol, a good example of a compound that has both a taste and an odor. Ethanol is a wondrous thing for purely intellectual reasons as well: neither sweet nor salty nor sour nor bitter, it once again refutes the false theory of the four tastes; more prosaically, perhaps, its physiological effects are somehow connected with the fact that ethanol seems to act on the trigeminal nerve, a nerve that comes from the rear of the skull and whose endings in the nose and the mouth detect pungency and coolness. And because ethanol is a colorless liquid that is less dense than oil, it has the very practical virtue of allowing us to create layered cocktails, beginning with the famous Irish coffee. Human beings value ethanol especially for its psychoactive effects, of course, but they are not alone: even horses and cows are fond of fermented fruits!
Whereas methanol molecules are built around a single carbon atom, ethanol molecules contain two of them. As the number of carbon atoms gets larger, the variety of alcohols continues to grow: they come in every size, with names such as “propanol,” “butanol,” “pentanol,” “hexanol,” “heptanol,” and “octanol.” The list goes on, for the chain of carbon atoms that forms the backbone of these molecules can be almost endlessly elaborated with branchings and various other embellishments. Earlier I mentioned 1-octen-3-ol (octenol), which has a marvelous odor of undergrowth—hence, its colloquial name, “mushroom alcohol.” The root oct- means that there are eight linked carbon atoms; the suffix -en means that two carbon atoms (whose position is indicated by the “3”) are joined by two bonds instead of one; ol designates the hydroxyl group typical of alcohols; the 1 specifies a further modification of the molecule’s structure at the first position. Once again, this alcohol is not merely sapid, but fragrant as well.
The world of alcohols is immense, and we risk getting, well, a headache if we go on cataloging them much longer. Let’s move on, then, to polyols, at least a few of which are already known to some modern cooks.
POLYOLS
Six polyols are commonly used by the food industry: sorbitol, mannitol, maltitol, isomalt, xylitol, and lactitol. Sorbitol, mannitol, and xylitol occur naturally in various fruits and vegetables, but samples that are obtained artificially through the hydrogenation of sugars come from starches. Thus sorbitol is derived from glucose, manitol from fructose, and maltitol from maltose.
Polyols can be used as sweeteners, but also as emulsifiers, stabilizers, moisturizers, thickeners, and texturizers. Unlike sucrose they do not cause dental cavities, and their calorie content is low—whence their appeal as an ally in combating obesity.
Isomalt (E953) is a combination of two hydrogenated saccharides: alpha-D-glucopyranosyl-1,6-sorbitol and alpha-D-glucopyranosyl-1,6-mannitol. It is obtained from sucrose in two steps: first, with the help of enzymes, the sucrose is transformed into isomaltulose, which then is hydrogenated to form isomalt.
Lactitol (E966) is a hydrogenated disaccharide obtained by lactose hydrogenation.
Maltitol (E965) is obtained by catalytic hydrogenation of D-maltose, a disaccharide present in malt that is made artificially through the saccharification of purified starch using an enzyme known as beta-amylase.
Mannitol (E421) owes its name to manna, the sweet-tasting exudate of the ash tree (Fraxinus ornus), of which it is the principal constituent. It is also found in olives, figs, and the sap of the larch tree, as well as in some edible mushrooms and in seaweeds of the genus Laminaria. Catalytic hydrogenation transforms a mixture of D-glucose and D-mannose into a mixture of D-mannitol and D-sorbitol.
Similarly, D-sorbitol takes its name from the berry of the rowan or mountain ash tree (Sorbus aucuparia), from which it was first extracted in 1872. A sugar found in many vegetables, it too is produced commercially through catalytic conversion of D-glucose (dextrose), itself obtained through enzymatic hydrolysis of starch.
Last but not least, xylitol (E967) is found in many fruits (greengages, strawberries, raspberries, and the like) as well as in cauliflower. It is commercially produced through catalytic hydrogenation of D-xylose, which is abundant in corn cobs, almond hulls, and birch bark. Xylitol, like sorbitol, has a refreshing effect on the palate.
INTENSE SWEETENERS
Sweetening compounds are legion, but the key word here is the adjective intense. Some compounds are several thousand times sweeter than sucrose. The degree of sweetness is crucial, for intensely sweet substances sweeten while providing little or no energy, which is to say they contain few, if any, calories needing to be burned off—a considerable advantage at a time when the plague of obesity shows no sign of abating.
No one knows to what extent traditional Western diets, which developed in an age when famines were still common, are responsible for our present predicament. It is plain, however, that unless food suddenly ceases to be overabundant, eating habits will have to change if we are to avoid dying from cardiovascular disease in even greater numbers than we do today.
From this point of view, note-by-note cooking has undoubted advantages. There is no reason why we should not make use of intense sweeteners, for innumerable studies have established that the toxicological risk associated with them is too small to warrant limiting commercial production, much less banning it altogether. All the compounds I discuss here are currently approved for commercial use in both Europe and the United States.
Acesulfame potassium, also known as acesulfame K (E950), was discovered by accident in 1967 by two agricultural research chemists at Hoechst AG in West Germany, Karl Clauss and Harald Jensen, and described in a paper they published six years later. Clauss happened to dip his finger into a batch of chemicals without noticing and then, licking it to pick up a piece of paper, tasted a mixture of remarkably sweet compounds. Together with Jensen, he managed to isolate the sweetest of them (two hundred times sweeter than sucrose), which also turned out to be the easiest one to use, acesulfame K. Molecularly very stable, it withstands both pasteurization and sterilization, decomposing only at temperatures higher than 200°C (392°F). The initial sensation of sweetness is followed, however, by a bitter aftertaste.
Aspartame (E951) was also discovered by accident two years earlier, in 1965, by James Schlatter, a chemist at G. D. Searle & Company, who was studying oligopeptide synthesis as part of an attempt to develop antiulcer drugs. Moistening his finger in order to turn the pages of a journal, he realized that he had unwittingly touched a sweet substance. Although aspartame is one of the most thoroughly tested food additives on either side of the Atlantic, it still comes under attack from time to time. The compound’s charms are nevertheless undeniable: a sweetening power 130 to 200 times greater than that of sucrose and a similar taste profile. It is unstable when exposed to prolonged heating, which releases phenylalanine and methanol, but the small quantities in which it is typically used in cooking make it no more dangerous than fruit jams, whose pectins are likewise sources of methanol.
Cyclamic acid and its sodium and calcium salts (cyclamates, for short), bear the number E952. Like so many intense sweeteners, cyclamates were also discovered accidentally, in 1937. Michael Sveda, a graduate student at the University of Illinois who was engaged in research on the synthesis of fever-reducing drugs, discovered that a cigarette he was smoking had a sweet taste after he picked it up from the lab bench.
Neohesperidine dihydrochalcone (E959) was discovered in 1963 by two American researchers, Robert Horowitz and Bruno Gentili, who were studying the relationship between the molecular structure of citrus compounds and bitter taste. Horowitz and Gentili had identified neohesperidine as one of the flavonoids found in bitter (Seville) oranges. To their astonishment, a derivative of this compound, neohesperidine dihydrochalcone, turned out to be sweet rather than bitter. It has an unpleasantly pronounced and persistent cool, licorice-like aftertaste, however, which can be offset only in combination with other sweeteners. Neohesperidine dihydrochalcone is also used for a purpose that falls outside the scope of the present chapter: in concentrations lower than those that make the sweet taste appear, it enhances odors.
Saccharin and its sodium, potassium, and calcium salts are assigned the number E954. Saccharin, the first of the intense sweeteners to be discovered, was accidentally encountered in 1878 by two chemists at Johns Hopkins, Ira Remsen and Constantin Fahlberg, who were investigating a class of coal tar derivatives known as toluene. At supper one evening after a day in the lab, Fahlberg happened to notice that his fingers tasted sweet. Commercial production by Monsanto Company began a quarter-century later, in 1902. Saccharin has a metallic and bitter aftertaste, less pronounced in the calcium salt than the others.
Sucralose (E955) was discovered almost a hundred years after saccharin, in 1976, in London. This time the discovery was the result of a misunderstanding: a chemist tasted a group of sugar derivatives instead of testing them, as he had been instructed to do. On further investigation he found that these halogenated sucrose derivatives (in which organic compounds form bonds with iodine, chlorine, and fluorine) include an insipid series, a bitter series, and a sweet series. Trichlorogalactosucrose, a chlorinated derivative of sucrose valued for its intensely sweet flavor, is now conventionally known as “sucralose.”
Thaumatin (E957) is an outlier on this list: it is a protein and therefore a large molecule. Thaumatin is extracted from the katemfe fruit (Thaumatococcus danielli), found in West Africa. The fruit itself was already known for its intensely sweet flavor, but it was only in 1972 that two sweet proteins, thaumatin I and II, were isolated by a pair of Dutch chemists, Henrik Van der Wel and Kees Loeve. Alas, it has a very strong licorice aftertaste, like rebaudioside A, extracted from the stevia plant, a native of South America, which quite recently has been recognized as an intense sweetener.
The sale of a number of intense sweeteners is prohibited in Europe, such as neotame (made by the American company NutraSweet) and alitame (made by Pfizer).
FLAVORING AGENTS
Earlier I explained why it is essential to distinguish between flavor (goût in French), a synthetic sensation, and taste (saveur), which is my subject in this chapter. Neither commercial producers nor regulatory bodies have yet really grasped the distinction, with the result that incoherence continues to reign, even in the scientific literature. I therefore persist in taking a clear, consistent, logical line in this matter, in the possibly forlorn hope that one day everyone will see things my way.
The category of additives coded E600–699 bears the official name “Flavor Enhancers.” Surely there can be no objection to speaking of taste enhancers or odor enhancers. But flavor enhancers? One commonly hears it said that salt, for example, is a flavor enhancer. It is true that an unsalted vegetable soup does not have a vegetable flavor; it only acquires one when salt is added in a quantity that nonetheless does not make the soup taste salty. Salt is therefore said to bring out the flavor of vegetables. In that case, is it the odor that is brought out or the taste? No one knows—although there is reason to believe that it may be odor because odorant compounds, which do not dissolve in water, dissolve even less easily when the water is salted—and so are able to be “salted out,” or extracted, from the liquid into the air.
However this may be, salt has another remarkable effect that can be experienced by conducting a test with tonic water, which contains quinine: add a bit of salt, and the water becomes sweeter and less bitter. In other words, salt is a taste enhancer because it enhances the sweet taste of the sucrose; but it is also a taste weakener, because it weakens the bitter taste of the quinine (which perhaps is why some people lightly salt their coffee). At all events, salt cannot be said to enhance a flavor if it diminishes a taste.
Even if the category of artificial flavoring substances that we are presently considering has been misnamed, it includes compounds that the note-by-note cook will want to make use of. I have already mentioned monosodium glutamate. It is the sodium salt of glutamic acid, an amino acid that is commercially produced by fermenting molasses and other liquids obtained from starch sugars. This acid, in the L form, is very commonly found in the natural world. It is salted out by the sodium ion, then purified and crystallized in the form of odorless white crystals. Depending on the individual, the sodium salt has a sweet or salty taste (some detect the taste of chicken broth); in every case, it intensifies the sensation of a particular taste. Other substances are reputed to have similar effects, such as sodium guanylate, sodium inosinate, isovaline, sodium DL-threo-8-hydroxyglutamate, sodium DL-homocysteine, sodium L-aspartate, sodium L-alpha-aminoadipate, L-tricholomic acid, and L-ibotenic acid. All these substances are derived from amino acids, and their action remains poorly understood.
Maltol, ethyl maltol, and furaneol enhance the fruit taste of jam and caramel and the rich, round notes that intensify the sensation of sweetness. Various substances affect the sensation of milk flavor: dioctyl sodium sulfosuccinate modifies the fresh milk taste, and NN-diorthotolylethylene diamine and cyclamic acid modify the butter taste. These compounds act in infinitesimally small doses, on the order of 0.0001 parts per million. Finally, let me mention diethyl glutamate, which can augment sweet and bitter tastes as well as the smell of ether, and methylpropyl alcohol, which acts in a way similar to sodium glutamate.
BITTERANTS
Is bitterness a sign of danger? It may be. Earlier I mentioned that many bitter alkaloids (compounds, extracted from plants, whose molecule contains one nitrogen atom) are toxic.
Nevertheless we are not just animals—and even our animality is singular. One has only to look at the many different sorts of food people eat to see that bitterness is by no means avoided. Beers are bitter. So are browned onions, to say nothing of the many aromatic plants, such as rue, that have been used in cooking since medieval times.
Nearer to our own day, the chef Édouard Nignon (1865–1934) sang the praises of bitter tastes in his remarkable book Éloges de la cuisine française, published a year before he died. Note that I speak of bitterness in the plural: like every good cook, Nignon knew (in his case without having to wait for the confirmation provided by biological research in the past few decades) that there are various kinds of bitterness, some persistent, others not; and that they stimulate different parts of the mouth and excite very specific sapictive receptors on the papillae.
In the food industry, the most commonly used bitter compounds are quinine (and its salts) for sodas and alpha-humulene for beers, but the rinds of citrus fruits contain many interesting compounds, among them naringin, which is found in grapefruit.
EXTRACTING BITTER COMPOUNDS
One of the difficulties facing note-by-note cooks today is that pure compounds are sometimes hard to come by. The Internet makes it possible to buy products from vendors halfway around the world, but it is worth keeping in mind that, if need be, we can always extract compounds ourselves. To take only the simplest example, heating grapefruit rinds in water produces a very bitter solution. Typically what is extracted in this way is a mixture of compounds, of course, rather than a pure compound. The technique of liquid–liquid extraction is commonly used in laboratories to separate the component parts: one liquid containing several dissolved compounds is combined with another liquid that does not mix with it; after the two solvents have been vigorously shaken, the compounds that dissolve more readily in the second one migrate to it.
In the kitchen, all you need are a glass jar and some water and oil. Take a grapefruit, for example, grind it up, and then put the crushed rind and flesh in the jar with equal amounts of water and oil. Screw the top on and shake the jar vigorously. Let the solids settle, and then separate the oil from the water. Taste the two liquids: each will have its own distinctive flavor! I leave it to you to try the same experiment with tomatoes (raw or cooked), fruits, or meats (again, raw or cooked). Whatever ingredients you choose, from one flavor you will obtain two new flavors. The water and oil that have been flavored in this way do not contain just one compound; they are what chemists call “fractions,” comprising all the compounds that these liquids dissolve respectively. There is no reason why we should not make use of fractions as well.
MATRIX EFFECTS
By now we have learned a few of the notes—sapid notes—that can be played on this marvelous piano we call cooking. It remains for us to mix them together. How do we go about doing this?
It would be altogether presumptuous for a chemist to give instructions in this matter, for how best to arrange the notes is an artistic, not a technical question. Even so, the chemist should not be bashful about calling attention to facts that may be useful to culinary artists. In particular, chefs should be mindful that the taste of a dish is not reducible to an isolated or momentary sensation. A dish must be constructed in such a way that its sensory effects will be registered over a succession of moments since the perception of flavor is an enduring sensation—or should be one if it is not.
With regard to the water in which sapid compounds are dissolved, the taste one perceives lasts only as long as the longest lasting of the sensations produced by the compounds that are mixed together in the water. But just as note-by-note cooking cannot be reduced to liquids alone, so there is no reason why the taste of a note-by-note dish has to be brief. The idea of producing solutions and nothing else holds no interest in any case. With enough imagination and ingenuity, the overall sensation can be very intricately structured, particularly if we exploit the properties of colloidal systems.
The key to success in this endeavor is to be found in what I call “matrix effects.” Let’s once again consider sodium chloride—the salt we use every day in our cooking. Depending on whether we are dealing with coarse salt or finely granulated salt or rock salt or hand-harvested sea salt (fleur de sel) or flake salt or the golden pyramid-shaped crystals known as Cyprus salt, the taste is not always the same, nor does it contribute to the perception of flavor in the same way because the chloride and sodium ions are not released at the same rate for every shape.
Varying the shape and size of different sorts of particulate matter is not the only possible way to shorten or lengthen the perception of taste and flavor, however. Dissolve some salt in water and now give the solution the form of a gel—by adding gelatin, for example. The particular microstructure, or “matrix,” of the gel causes the salt to be released into the gelatinized water more slowly; in other words, it produces a different salty sensation. We can introduce an additional degree of complexity by making the gels more or less firm, using gelatin as before or some other gelling agent. In this way a whole range of release rates for the salt can be devised. If they are skillfully combined it will be possible to make dishes having an immediate sensation of saltiness that gradually disappears and then suddenly returns.
These mechanisms are simple enough. But matters become rather more complicated once one is acquainted with chemical bonds—particularly, in the case of salt, once one knows how to combine ions (in this case chloride and sodium) with various molecules, whether these molecules are added in solution to the liquid trapped in the matrix of a gel or whether they themselves constitute the solid walls of the gel’s matrix.
All this goes to show that note-by-note cooking can attain an unrivaled degree of precision with respect to taste. Something similar may in fact be possible using the methods of traditional cooking, but only with immensely greater difficulty and without being able to separate tastes from odors. With note-by-note cooking, by contrast, the independence of sensory registers—think of them by analogy with the registers of an organ, a set (or “rank”) of pipes—multiplies occasions for creativity by whole orders of magnitude!
A NEW BASIC TASTE
The world of tastes is still, as I say, poorly understood. Should we deplore this state of affairs, or should we rejoice in the opportunities it provides for making new discoveries? Optimists will prefer to adopt the latter view, and their hopes will grow further when they learn that fats, which have long been reputed to be flavorless, turn out to be rather less insipid than was believed only twenty years ago.
More precisely, what has been discovered is a new modality or sensory faculty: human powers of gustatory perception include the ability to perceive the taste of what are technically known as long-chain unsaturated fatty acids. What exactly is meant by this term? Let’s begin with an oil. We saw earlier that its constituent molecules, triglycerides, resemble microscopic combs with three teeth. Such molecules can be formed by causing a reaction between glycerol (the shaft of the comb) and fatty acids (the teeth). Fatty acids? Think of a linear chain, a sort of backbone, formed by joining carbon atoms together. To one of the last carbon atoms let’s attach a carboxyl (—COOH) group, in which a carbon atom is bound to an oxygen atom on the one side and to a hydroxyl group (an oxygen atom and a hydrogen atom) on the other. Next, let’s attach hydrogen atoms to the carbon atoms so that each of the carbon atoms is duly bonded to four other atoms in all. We now have a saturated fatty acid. To get an unsaturated fatty acid, remove one hydrogen atom from two neighboring carbon atoms and join these carbon atoms by means of a new bond.
Chemists in France recently discovered that such compounds are “recognized” by sapid receptors on the papillae. Initial studies were conducted on mice, but experimental evidence regarding human perception continues to accumulate. At first it was unclear whether one was dealing with a taste—the taste of fat—or with something else. It is now quite clear, however, that fatty matter does not consist only of a group of compounds that we appreciate by virtue of a sort of nutritive reflex, so that eating fat triggers an agreeable sensation like the one provoked by the ingestion of modified starches, which sl Press, owly release glucose into the digestive system. No, the perception of fat does seem in fact to constitute a new sensory modality—a sixth basic taste, as it is often referred to.
In addition to the compounds I have discussed in this chapter, there are many others, natural and synthetic alike, that are now known to have novel and distinctive tastes. How many other such discoveries await us in the years ahead?
Written by Hervé This (translated by M. B. DeBevoise) in "Note-by-Note Cooking - The Future of Food" (La cuisine note à note), Columbia University Press, 2014, excerpts chapter three. Digitized, adapted and illustrated to be posted by Leopoldo Costa.