Kitchen Mysteries_ Revealing the Science of Cooking Part 3

First, imagine what would happen if water evaporated from the top of the souffle preparation. No swelling would take place. Thus the highest souffles will result from heating the ramekins from below. Put them directly on the lowest rack in a heated oven.

Second, the bubbles have to be trapped for them to be able to make the souffle rise. Thus the egg whites must be beaten into very firm peaks, so the bubbles will be trapped in the very firm foam.

Third, the increase in volume is diminished if the bubbles escape from the top. Thus allowing a crust to form on the top of the souffle, as proposed earlier, will promote successful rising.

To summarize, then: heat from below, use firmly beaten egg whites, and let a crust form on the top of the souffle.

Cooking The Secrets of Tenderness As mentioned earlier, in cooking we have three objectives: to kill harmful microorganisms that contaminate food, to change the consistency of foodstuffs, and to give them flavor. Often the cook achieves these ends simultaneously, because heat, which kills microorganisms, for example, also degrades meat's toughest molecules and triggers chemical reactions that engender aromatic compounds.

Why does cooking tenderize meat? Why does it make vegetables lose their rigidity? And, more generally, what is the secret of culinary transformations?

The culinary arts begin and end with the art of cooking, and it certainly isn't feasible to summarize the whole book in this one chapter; such an extraction would be too concentrated. I will only attempt a preliminary clarification, saving the various types of cooking for later chapters.

In every case, heat increases the mobility of atoms and molecules, which can thus react because they now have enough energy to be transformed. The molecules b.u.mp into one another, break apart, and, when chemical groups with some affinity come into random contact because of the erratic movement of the molecules, rearrangements take place. These rearrangements are called chemical reactions. They produce new compounds.

How Do We Heat Foods?

The question seems naive, but try, for example, to heat a thick soup by holding a small electric heater over its surface. The very top layer will boil, but the rest of the soup will remain cold. Likewise, a good roast on a spit must be done in front of the fire rather than directly over it. If you roast quail, the most delicate of birds, barded as it should be with grape leaves between the fat and the bird, you will get only the taste of smoke if you cook it directly over the fire. But if you know the mechanics of radiation and put the spit at the same height as the flame and beside it, your fowl will roast gently, through to the center, and the flesh will be delicately flavored with the subtle taste of grape leaves.

This is why it is especially useful to know that heat is transmitted to dishes through three mechanisms: conduction, convection, and radiation.

BILLIARD b.a.l.l.s IN THE SAUCEPAN.

Conduction is the phenomenon that occurs when a solid is heated. A metal spoon left in a boiling liquid will burn your fingers. Likewise, the heat conveyed by an oven to the surface of a roast, for example, is gradually transmitted to the molecules of the interior. In effect, the outside molecules, agitated by the heat, collide with molecules located deeper within and thus transmit their energy to them. Those molecules, colliding with molecules even closer to the center, pa.s.s along the activity and thus the heat.

Heat is the agitation of molecules. Foods are like heaps of billiard b.a.l.l.s. If you agitate the outer b.a.l.l.s, they will transmit their agitation to the adjacent b.a.l.l.s closer to the center of the heap, which will then transmit their energy to the b.a.l.l.s still closer to the center, and so on. This is the phenomenon of heating through conduction.

CONVECTION AND SKIMMING.

In liquids, it is convection that accelerates the transmission of heat. When a saucepan full of water is heated from the bottom, the water at the bottom heats first, through contact with the bottom of the pan, which is itself in contact with the stove. Naturally, the heat is transmitted through conduction, but beyond that, the hot water at the bottom, less dense than the cold water found above it, rises and is replaced by the cold water, which is then heated. The liquid currents, called convection currents, circulate in the liquid and rapidly distribute the heat.

This phenomenon is apparent when you skim a sauce. Say you are making a braised dish, for example. First you sear a piece of meat and its tr.i.m.m.i.n.gs in the oven (see the chapter on braising). After five minutes of searing, you add one-fourth of a liter (about a cup) of good white wine, cover the pan, and continue the cooking at a very low boil by lowering the oven temperature to between 60C (140F) and 100C (212F), depending on the coagulation point you desire. After an hour of this slow cooking, you combine half the liquid with a roux (made by cooking a little flour in b.u.t.ter until it is a pleasing golden color). The roux will thicken the liquid drawn from the meat pan. Skimming it will produce a sauce that is light, smooth, and satiny; the process must be slow and consistent. First, you tilt the saucepan to one side (by raising the opposite side with an object that does not mind the heat, like an old spoon). Heated in just one spot, the liquid forms a single convection cell that absorbs the heat from below at the point of contact, rises vertically and descends along the sides. This prompts the coagulation and aggregation of all the unwanted solid matter, which is returned to the center of the convection cell and forms a sc.u.m that can be regularly drawn off. At the same time, you dab the surface of the sauce with absorbent paper toweling to remove the fat that appears as unemulsified droplets. With this slow process, you allow the time for many chemical reactions to occur ... and to generate a wonderful flavor.

Convection was discovered by Count Rumford (Benjamin Thompson), an inspired adventurer who, among his many other scientific studies, pondered the question of why his applesauce remained hot long after his soup had cooled.23 We know now that convection is most active when the medium is least viscous. In a viscous medium, the liquid circulates with more difficulty. In the case of Rumford's thin soup, convection rapidly exchanged the heat of the bowl and the air, whereas the heat of the thick applesauce could escape only through conduction and thus slowly. So the sauce stayed hot longer than the soup. We know now that convection is most active when the medium is least viscous. In a viscous medium, the liquid circulates with more difficulty. In the case of Rumford's thin soup, convection rapidly exchanged the heat of the bowl and the air, whereas the heat of the thick applesauce could escape only through conduction and thus slowly. So the sauce stayed hot longer than the soup.

A LIGHT THAT COOKS.

The third method of heating involves radiant heat, which is what makes the front of you warm but leaves the rest of you cold when you are facing a fire. Heating through radiation is the principle behind roasting meat. A fire or a grill emits heat rays a.n.a.logous to light rays but invisible: infrared rays. Like light, they disperse in straight lines and are stopped by opaque bodies. When they are absorbed by meat, their energy heats and cooks it.

Cooking with microwaves, of course, is also a process of heating with radiation. But in that case the waves penetrate the foods in much the same way as light pa.s.ses through gla.s.s windows.

What Kind of Cooking for Which Dish?

Once the heat is in the food, it fulfills various functions that are all part of the cooking, among them, softening hard substances, coagulation, inflation or dissolution, transforming the appearance, reduction or extraction of juices or nutritional elements.

Convection, conduction, or radiation? The following a.n.a.lysis considers most of the cooking processes. The heating medium will generally be a fat, a liquid, dry air, or moist air.

When the heating medium is a hot solid, conduction produces a grilled dish.When the heating medium is hot liquid fat, convection and conduction produce a sauteed dish if the food is simply lying in the fat.When the heating medium is hot liquid fat, convection and conduction produce a deep-fried dish when the food is immersed in the fat.When the heating medium is warm liquid fat, convection and conduction produce such wonderful dishes as confits.When the heating medium is a boiling liquid, convection and conduction produce a boiled dish.When the heating medium is a simmering liquid, convection and conduction produce a poached dish.When the heating medium is steam, convection produces a steamed or braised dish.When the heating medium is moist air, convection is responsible for the cooking of oven roasts.When the heating medium is dry air, radiation is responsible for roasting foods on a spit.

Keeping in mind that "The discovery of a new dish does more for human happiness than the discovery of a star" (Brillat-Savarin),24 let us not forget microwaves, which cook in a unique fas.h.i.+on. Radiation is absorbed by certain molecules within the food (water molecules), and the heat of these molecules then cooks the entire food by being transmitted through conduction to the molecules unaffected by microwave radiation. let us not forget microwaves, which cook in a unique fas.h.i.+on. Radiation is absorbed by certain molecules within the food (water molecules), and the heat of these molecules then cooks the entire food by being transmitted through conduction to the molecules unaffected by microwave radiation.

Cooking Without Heat?

No list of cooking processes would be complete if it failed to mention one slightly peculiar process: cooking with chemicals.

Do not be frightened by the name. Cooking with acids, for example, is simply a matter of placing foodstuffs in lemon juice or vinegar. In these two cases, the liquid, an acid, is responsible for making the proteins coagulate. That is how fish left in lemon juice is transformed, just as if it had been poached in boiling water, although its flavor is very distinctive.

The Boiled and the Bouillon Fifty Hams!

For a long time, meat was believed to be made up of two parts: the part that pa.s.sed into the bouillon when meat was cooked in water for a long time and the fibrous part, which was called le bouilli le bouilli, or the boiled. Gourmands did not have words harsh enough for le bouilli le bouilli. Stripped of its succulent elements, boiled meat no longer deserved a place on their tables.

Brillat-Savarin relates the following anecdote in honor of the "osmazome," which was supposed to be the princ.i.p.al component of taste in meats: The Prince of Soubise planned to give a great party one time; it was to end with a supper, and he asked for the menu.His steward appeared at his morning conference with a handsomely decorated sheet of paper, and the first notation the prince's eyes fell upon was this: fifty hams fifty hams."Look here, Bertrand," he said, "it seems to me you are dreaming! Fifty hams! Are you trying to treat my whole regiment?""Not at all, sir! Only one ham will appear on the table, but the rest are essential for my sauce espagnole sauce espagnole, my white sauces, my garnishes, my ...""Bertrand, you're thieving from me, and I shan't let you get away with it.""Ah, my lord," the artist said, hardly able to hold back his wrath, "you know very little of our resources! Command me, and I can put these fifty hams which seem to bother you into a gla.s.s bottle no bigger than your thumb!"What was there to say to such a positive a.s.sertion? The prince smiled, nodded, and the menu was approved.25 A bit further on, Brillat-Savarin considers the osmazome more explicitly: The greatest service rendered by chemistry to alimentary science is the discovery or even more, the exact comprehension of osmazome.Osmazome is that preeminently sapid part of meat which is soluble in cold water, and which differs completely from the extractive part of the meat, which is soluble only in water that is boiling.It is osmazome which gives all its value to good soups; it is osmazome which, as it browns, makes the savory reddish tinge in sauces and the crisp coating on roasted meat; finally it is from the osmazome that come the special tangy juices of venison and game.This property is found mainly in mature animals with red flesh, blackish flesh, or whatever is meant by well-hung meat, the kind that is never or almost never found in lambs, suckling pigs, pullets, or even in the white meat of the largest fowls. It is for this reason that lovers of poultry have always preferred the second joint: in them the instinct for flavor came long before science confirmed it.It is also the infallible goodness of osmazome which has caused the dismissal of so many cooks, destined as they were to ruin their basic soup stock; it is osmazome which has made the reputation of the richest consommes, which once made toast soaked in bouillon a favorite restorative during weakening curative baths, and which inspired Canon Chevrier to invent a soup pot which locked with a key. (It is this same holy Father who never used to serve spinach on a Friday unless it had been cooking since the Sunday before, and put back each day on the stove with a new lump of fresh b.u.t.ter.)Finally, it is to husband this substance, as yet largely unrecognized, that the maxim has been propounded that in order to make a good bouillon the pot must only smile smile with heat, a truly worthy expression considering the country from which it came. with heat, a truly worthy expression considering the country from which it came.Osmazome, discovered at least after having for so long delighted our forebears, can be compared with alcohol, which tipsified many generations of men before any of them knew how to strip it naked in the a.n.a.lytical process of distillation in a laboratory. During the action of boiling water osmazome gives place to what is understood more especially by extractive matter: this last product, reunited with the osmazome, makes up the juice of meat. During the action of boiling water osmazome gives place to what is understood more especially by extractive matter: this last product, reunited with the osmazome, makes up the juice of meat.26 A Universal Flavor?

Even if it is scholarly and learned, this long treatise by our master gastronome is very wrong. Brillat-Savarin's osmazome is only a myth created in the era when a.n.a.lytical chemistry was in its infancy. It was the French chemist Louis Jacques Thenard who coined the term "osmazome," based on the Greek osme osme, "odor," and zomos zomos, "soup." He proposed it for the first time in an article in the Bulletin de la Faculte de medecine de Paris Bulletin de la Faculte de medecine de Paris in 1806. in 1806.

In his use of the term, Brillat-Savarin seems to suggest that the osmazome is a unique, well-defined compound, like the ethyl alcohol in alcoholic drinks. But modern methods of a.n.a.lysis show that the part of meat extracted cold is already a complex mix of water, lipids, various odorant molecules, salts, and more. In total, meat contains hundreds of sapid or odorant compounds. As for the first extract being the most sapid, let us trust our ancestors on this. They were more accustomed to boiling meat than we are, and, what is more, volatile molecules are often better perceived than the molecules the food retains, which activate neither the taste buds nor the nasal receptors.

On the other hand, Valery's aphorism according to which "what is simple is always false" applies here to the osmazome. It is not the sapid element in meat; it is only one of the various flavorsome extracts that can be drawn from it.

And, if we are to believe Brillat-Savarin, it is the best.

How Does One Obtain a Flavorful Bouillon?

Let us think this through: meat contains many proteins. That is well known, and we eat meat for the protein it provides us. But what else does it contain? Amino acids, as these are produced when proteins are cooked for a very long time. These compounds are important because, as we have seen, they provide taste. What else? Fat! Just as important, but less well known, is the fact that meat fats are the main storage sites for odorant molecules. Beef tastes like beef because its fat contains the odorant molecules characteristic of beef. Mutton tastes like mutton because its fat contains the odorant molecules characteristic of mutton. And if little birds-larks, robins, buntings-each have their own delicate flavor, that is also because their fat contains the molecules characteristic of this small game.27 How to obtain a flavorful bouillon when the odorant compounds are in the fats, which are eliminated after cooking, once they have congealed?

First of all, let us note that compounds insoluble in water are never completely insoluble. In the presence of oil and water, they divide in specific proportions in each of the two substances. To extract a compound from oil that is not very soluble in water, one must simply agitate the oil in the presence of a large quant.i.ty of water. Then, when the extraction has been achieved, one can eliminate the oil and concentrate the water ... and the flavors.

In practice, we can trust Brillat-Savarin when it comes to obtaining a good bouillon, even if his instructions only give the appearance of being scientific: The water first of all dissolves part of the osmazome; then the alb.u.men, which coagulates at about 104 degrees Fahrenheit, forms a sc.u.m which is usually skimmed off; then the rest of the osmazome dissolves with the juice or extractive part; and so finally do portions of the outer coating of the fibers, which are pulled off by continuous movement of the boiling liquid.To make a good bouillon, the water must heat gradually, so that the alb.u.men will not coagulate inside the meat before it can be extracted; and the boiling must be kept at a simmer, so that the various parts which are successively dissolved may mix together easily.28 Does modern science confirm these precepts? It teaches us that the muscle fibers (the cells that make up the muscles) are composed of two proteins essential for contraction, actin and myosin, which are coated in collagen fibers.

It is the collagen that rigidifies meat and makes it tough. And it is to tenderize the collagen that meat is cooked for a long time in water. Over a long period of cooking, the collagen gradually pa.s.ses into the bouillon at the same time as it is partially decomposed. That is how gelatin is extracted from meat (or from bones, skin, and tendons, where gelatin is abundant).29 So why does the boiled beef in a stew retain its fibrous texture? Because, even if the collagen is solubilized, the proteins within the muscle fibers coagulate and are not solubilized.

Why should bouillon be covered when cooking? Because, as the bouillon boils, odorant molecules escape with the steam. As chefs will tell you, however, covering bouillon turns it cloudy. Why does it turn cloudy? That I do not know. How do you clarify a bouillon if it should become cloudy? By beating in an egg white, which coagulates around the particles that cloud your bouillon. You can also use good filtering tools from a chemistry laboratory, which are more effective and do not waste egg whites.

Finally, why don't the volatile molecules of the meat escape from the bouillon when the bouillon only simmers? That is the crux of the whole matter. First one should remember that the fat that melts during cooking remains in the stock as fat droplets, dissolving odorant molecules. Certain volatile-and odorant-molecules actually do leave the bouillon, but they react as well. They make new odorant molecules that enrich the stock, according to Brillat-Savarin, who was not entirely mistaken. Over the course of the cooking, Maillard and other browning reactions produce many sapid molecules that enrich the bouillon. The bouillon's flavor is primarily the result of this cooking process. Someday, compare the water a piece of meat has been steeped in cold, in which such browning reactions have not taken place, and a bouillon prepared according to these worthy, time-honored principles.

Can You Lose Weight by Eating Only Boiled Meat?

That is a serious question in our times, when we often do not get the physical exercise that would permit us less restraint at the table. We have seen that meat contains abundant protein but also fat, which gives it its desirable flavor. Could this flavor be retained by boiling meat?

In red meat heated to 150C (302F) or in white meat heated to 240C (464F), the fats melt and are released from the flesh. In cooking, meat gets rid of its fat. If grilled meat is sometimes criticized for being too fatty, it is precisely because it is coated with the fats that have issued from it.

Can the problem be remedied by boiling meat? Not necessarily. For a bouillon, the maximal temperature is 100C (212F), so the fats melt less and are released from the meat less easily. Additionally, the mineral salts and aromatic compounds of the meat cells can escape from the meat and pa.s.s into the bouillon. In sum, we obtain a less flavorful-and also less healthy-food.

It is better to wipe grilled meats with absorbent paper. This will allow you to retain the good taste (the taste produced by grilling, not the taste of the fats that you'll eliminate) while preserving your figure.

Steaming How Does One Tenderize Without Sacrificing Flavor?

Boiled meat can be tender, certainly, but it has no flavor. In the last chapter, we saw that the tough part, the connective tissue and especially the collagen, is dissociated as it reacts with the water, but the odorant and sapid molecules escape from the meat into the bouillon. All that remains are tasteless fibers.

Can the flavor of the meat be retained even while it is tenderized? That is the principle behind cooking with steam, no different from cooking in a sealed pot (a l'etouffee), a long cooking process in an atmosphere saturated with water vapor. During this operation, the saucepan acts as a papillote, a sealed tinfoil or parchment packet. The same principle is at work in a Texan barbecue, when the meat, set on a grill in a big canister full of coals, cooks for sometimes as long as two days at just 70C (158F).

Thus, for steaming, it is sufficient to have the food steep for a long time in vapor. Naturally, the hotter this vapor is, the more rapidly the food cooks. That being the case, you need a lively boil. Of course, the food must be above the liquid, or else you end up with boiled meat!

Often recipes recommend browning meat in b.u.t.ter before adding the liquid and a little salt. This is not a bad idea. First, the tenderizing can get started in this first stage of cooking at a high temperature, and, what is more important, it promotes Maillard reactions and the browning that produces the characteristic odor of grilled meat.

After the preliminary browning, liquid is added, above which the meat is raised-in the basket of a pressure cooker, for example, not used under pressure-and cooked for a long period-four to five hours-during which time the collagen tissue is dissolved. This method is especially suited to dishes in which flavors like those in a bouquet garni are to be highlighted. The herbs, spices, and seasonings are added to the liquid so that their aromatic compounds can be extracted by the water vapor (extraction by vapor is a method for separating compounds widely used in chemistry laboratories and also in the perfume industry), conducted around the meat, and recycled. Brought to a temperature never higher than 100C (212F), they are not degraded and gradually permeate the surface of the meat. Let us not overlook a method that offers such advantages!

Braising Meat for Cooking Meat?

I would love to introduce you to the notion that the supreme cooking method is braising. In this transformative operation that takes place in a closed receptacle, with almost no liquid, the meat loses as few elements as possible. Instead of the elements of the meat escaping into the liquid, the meat absorbs the best of the liquid.

Before going further, let us recall cooking's old familiar refrain: to kill microorganisms, provide flavor, and make tender. In braising, these operations take place in two stages: cooking at a high temperature, which kills microorganisms, browns the meat's surface, and creates odorant and sapid molecules through Maillard reactions; then a very long phase of tenderization and taste production using gentle heat. The result measures up to the effort: the meat, marvelously flavorful, melts in the mouth.

People often believe that braising requires immense care, and this fear often makes them subst.i.tute roasting for braising. There is no need for this. If one sets about it methodically, braising requires no more attention than roasting, and its success is certainly more guaranteed. What is true, nevertheless, is that braising comes at some expense: braised meat cooks in the sapid juices of some other meat.

The principle of braising, then, is to cook the meat while at the same time nouris.h.i.+ng it with fortified juices. This is a long way from cooking in water! It is not only the method of cooking that characterizes braising but, just as important, what is added to the pot: bacon, meat juices, wine, brandy, all of which give succulence to the piece of meat being cooked in it. Succulence is the true goal of braising, the one toward which all the operations and various methods are aimed. According to the great Careme, to braise is "to put strips of bacon in the bottom of a ca.s.serole and, on top, slices of meat. Then one adds either a goose, a turkey, a leg of lamb, a piece of beef, or something similar. Then one adds slices of meat and strips of bacon, two carrots cut in pieces, six medium onions, bouquet garni, basil, mace, coa.r.s.ely ground white peppercorns, a touch of garlic; then half a gla.s.s of well-aged brandy and two large spoonfuls of consomme or bouillon. Then it is covered with strong paper that has been b.u.t.tered, and cooked from above and below."30 These instructions are not presented as a recipe to follow step by step; rather, they give us an idea of the philosophy of braising. Let us consider a recipe: in a large pot that will be closed and go in the oven, one puts a fatty substance (oil or goose fat, for example), a layer of onions, a layer of carrots cut into rounds, ham, the piece of beef that will be eaten, strips of bacon, another layer of ham, another layer of carrots, and a final layer of onions. Without covering it, the whole thing is placed in a very hot oven to brown. Then bouillon, meat juice, white wine, and possibly brandy are added. Then the covered dish is put back in the oven, at very gentle heat, so that the braising is indicated by only a very slight trembling. At the end of the cooking, the remaining juices are recovered and bound with a light roux. Then the sauce is skimmed while the meat is kept hot.

What Happens During Braising?

The principle behind braising, I repeat, is to tenderize the meat and make a very flavorful sauce. Here I must cite some new scientific results, which disprove some old theories. Previously, it was thought that there were two main kinds of cooking: by expansion and by concentration. In the first case, however, exemplified by boiling meat, no expansion of the meat takes place. On the contrary, it shrinks, because the collagen contracts when it is heated and the juices that flavor the stock leave the meat. In roasting or in braising, on the other hand, there is no concentration, as it was thought, but again some contraction because the collagenic tissue shrinks.

It is better simply to remember that, the higher the cooking temperature, the greater the loss of juices. In braising, the low temperature that should be the rule keeps as many juices in the meat as possible, while the collagenic tissue dissolves slowly, releasing gelatin and amino acids that give the sauce taste and a satiny texture.

Braised Meat Without Sauce?

Braised meat without sauce? That would be a crime against gourmandise. In fact, the sauce for braised meat is not difficult to prepare: either the juices thicken enough naturally to be served as they are or binding them with a bit of potato flour, roux, or beurre manie completes the preparation of this delicious, mouthwatering dish.

Let us remember that a roux is prepared by cooking flour very slowly in b.u.t.ter. The mixture of b.u.t.ter and flour must form bubbles that rise gently and then collapse again. The roux is ready for the liquid it will bind when it has a nice hazel or light brown color, according to the taste desired. After the juices have been added to the roux, skimming completes the sauce's preparation. The thickened sauce is heated for a very long time, keeping only one corner of the saucepan in contact with the heat, so that a single convection cell agitates the liquid. The top of this cell is skimmed to eliminate all solid particles that cloud the sauce. By eliminating excess flour and fat particles, this operation has the huge advantage of producing a healthy product that is, at the same time, flavorful.31 Beurre manie, a raw b.u.t.ter-and-flour mixture, is used when there is not time enough to make a roux. b.u.t.ter and flour are mixed with a fork, the liquid to be thickened is brought to a boil, and b.a.l.l.s of the blended b.u.t.ter and flour are added to it.

Chicken Stew, Beef Stew, Veal Stew How Do We Salt Them?

When should salt be added to a beef stew, a veal stew, or one of those chicken stews of good King Henry?

Try this if you have not already considered this question. One day when you have a little more time than usual at your disposal, make double the amount of a dish and experiment with the effect of salt. In two saucepans heated in identical fas.h.i.+on, place the same ingredients in equal quant.i.ties, but salt one of the dishes before cooking and the other one after. You will soon see the difference ... and the importance of osmosis. It is a matter of simple physics, as a familiar experiment will reveal. When a drop of colored liquid is added to pure water, and they are left together for a bit of time, we discover that the coloring agent eventually spreads throughout all the liquid.

The molecules of the coloring agent, agitated by incessant movement and randomly b.u.mping into the water molecules, spread throughout the water, and their concentration becomes equalized throughout the solution. This phenomenon of diffusion is very common. In a medium where molecular movement is possible, compounds gradually distribute themselves so that their concentration is everywhere equal.

Let us complicate the experiment a little by dividing a U-shaped tube in half with a permeable membrane that only lets water pa.s.s through and stops any larger molecules, like those of the coloring agent, putting water in one compartment and the coloring agent in the other. In order to distribute itself equally throughout, the water will go into the compartment containing the color to equalize its concentration; the color molecules, however, will remain in their initial compartment because they will be stopped by the membrane.32 In the end, the compartment that first contained only the coloring agent will gain a bit of water, so the levels will be different. This is the phenomenon of osmosis. In the end, the compartment that first contained only the coloring agent will gain a bit of water, so the levels will be different. This is the phenomenon of osmosis.

The dilemma of when to add salt to the stew is as follows: if the dish, basically a piece of meat in water, is not salted at the start, the mineral salts pa.s.s into the solution in which the meat steeps. At the end of the cooking time, the meat is tasteless. On the other hand, if it is salted before cooking, the gravy will suffer because the meat's juices will remain within the meat.

You must thus proceed according to the spirit of the dish that you are preparing. If you want to enrich the bouillon, add salt only at the end of cooking. If you want to retain the full flavor of the meat, add salt right away. And if you want a good chicken stew, with a flavorful sauce, add salt a little before the end, so the juices are harmoniously divided between the two components of the dish.

Questions of Pressure Why Use a Pressure Cooker?

The pressure cooker is an antimountain. At higher alt.i.tudes, the air becomes rarified, and the air pressure is lower than that at sea level, so water molecules, for example, more easily escape the body of liquid in which they are found. In short, water boils at a temperature lower than 100C (212F). In a pressure cooker, the water that evaporates at the beginning of the cooking gradually increases the pressure in the pot, so water molecules have more difficulty escaping the liquid. The boiling point of the water is thus increased. In practice, today's pressure cookers are devised so that water boils in them at 110C (230F) to 130C (266F).

This increase in the boiling temperature has some advantages. Chemical reactions take place about three times faster in water at 130C (266F) than in water boiling at 100C (212F). Vegetables, for example, cook much more quickly.

On the other hand, the pressure cooker has some disadvantages that make cooks condemn it. First of all, you cannot see what is happening inside it and controlling the cooking process is more difficult. Five minutes too long in the pressure cooker is like fifteen minutes of traditional cooking. In addition, certain reactions that take place in an uncovered saucepan, involving the air in the kitchen, do not occur in a hermetically sealed pressure cooker.

Moreover, all reactions are not accelerated in the same way by the increase in temperature. The softening of vegetable fibers is more accelerated than the permeabilization of the vegetable cell walls. The vegetables are tenderized, but they remain tasteless. Some cooks will only pressure-cook a roast as a last resort. For others, it is a method of choice; they maintain that a pressure-cooked roast is less dry than an oven roast.

Let us not sit in judgment of the pressure cooker here. Let us only try to understand the principle behind it.

Cooking in the Mountains?

Since we have considered cooking under increased pressure, why not also consider cooking under decreased pressure?

Those of you who suffer from vertigo may rest easy. I am not inviting you into high alt.i.tudes. I am only proposing a simple device, the vacuum pump, which reduces the pressure in a receptacle to which it is attached. Present in all chemistry laboratories, the vacuum pump is a simple tube that can be connected to a faucet to allow water to run slowly (great for watering your culinary herbs, for example). This tube includes a lateral branch where a plastic tube is fitted, the other end of which can be attached to the opening of a pressure cooker where the safety valve is usually located. As it flows, the water takes in the air and creates a partial vacuum in the pressure cooker. Because of the phenomenon mentioned at the beginning of this chapter, the boiling temperature is lowered. This time, the chemical reactions are slowed down in various ways; new tastes appear.

We tested this ingenious a.s.sembly of Nicholas Kurti's during the First International Conference on Molecular and Physical Gastronomy, held in Erice, Sicily, in 1992, but the results remain unexamined. We know that a bouillon reduced under low pressure has a different taste, but the circ.u.mstances that call for such tastes have yet to be discovered.

Cooks, the ball is in your court!