Kitchen Mysteries_ Revealing the Science of Cooking Part 10

Does it, too, contain proteins that sequester the tea's colorant molecules? No, the explanation is of another order, more chemical than physical. Let us notice, first of all, that the tea to which lemon juice is added does not become colorless, or even yellow, like the lemon juice. Its red color turns to orange, because its red pigments are weak acids (acids are molecules that contain a hydrogen atom capable of dissociating under certain conditions). In the presence of lemon juice, that is to say, a stronger acid, the yellow color of the nondissociated form becomes apparent.

By adding bicarbonate to tea-and I do not guarantee the gastronomic results of this experiment-we obtain the reverse effect. An intense brown color develops as a result of the dissociation of the acid groups and the appearance of the other dissociated form of the pigments.

How Can We Not Spill the Tea When Pouring It?

The "teapot effect" is one of the most disagreeable phenomena encountered in cooking. With certain teapots, the one pouring knows in advance that the boiling liquid will spill on the knees of the guests or at least on the carefully washed and ironed tablecloth.

Physicists who recognize this effect have found an answer, but it is a Pyrrhic victory: they try teapots out before buying them. The effect was studied by Marcus Reiner in 1956 at the Technical Inst.i.tute of Israel. Then, in 1957, Joseph Keller of New York University explained the phenomenon.

In physics, the flow of a liquid is characterized by the current lines, which are tangential to the velocity vector of water. More concretely, you can form an image of these lines by putting small colorant particles into a flowing liquid; the streaks of color are the current lines.

When water flows over a horizontal surface, the current lines are horizontal and parallel, but when the liquid encounters an obstacle, the lines draw together and the speed of the liquid increases; simultaneously, the pressure diminishes. This increase in speed is well known to all sailors. When a current rounds a point, the water accelerates ahead of the point.

The decrease in pressure, imperceptible to the sailor, becomes evident, alas, when you pour tea. In pa.s.sing near the lower edge of the spout, the current is pulled downward by the weight of the liquid, so that it accelerates and its pressure decreases.

The pressure decreases at the edge of the spout, did we say? Since liquids have a tendency to be displaced from zones of high pressure to zones of low pressure, the tea that accelerates is plastered to the side of the teapot. That is what scientists call the Bernouilli effect, and it lets them make a liquid flow the length of a long gla.s.s tube. In the case of tea, the liquid faithfully follows the contour of the teapot ... and ends up on the table!

Cold and Cool Cool, but How Cool?

How to keep fruits and vegetables for a long time? By putting them in a cool place as quickly as possible, by isolating the ones that are already damaged, and by carefully cleaning the containers where they are kept. Of all the benefits of science and technology, one of the most misunderstood-because it is so familiar-is refrigeration.53 Nevertheless, only the carefully considered use of refrigeration produces good results. Here is a way to use it that owes much to the findings of the team of agronomists at the INRA research center in Monfavet and to the work ent.i.tled Nevertheless, only the carefully considered use of refrigeration produces good results. Here is a way to use it that owes much to the findings of the team of agronomists at the INRA research center in Monfavet and to the work ent.i.tled On Food and Cooking On Food and Cooking, by Harold McGee, mentioned earlier. This book is a survey of everything related to food and its culinary transformations.

What we hope to avoid, through cold temperatures, is, for example, the degradation of plant tissues. Ideally, fruits and vegetables should be consumed straight from the garden, but as long as cities are not transformed into immense fields, we face the need to conserve our foods.

The composition of foodstuffs changes considerably within a few hours of being harvested because the plant cells continue to function even though they are no longer receiving water from the plant's roots. Corn and peas, for example, lose up to 40 percent of their sugars in six hours at room temperature. What is worse, asparagus and broccoli, once picked, use these sugars to synthesize indigestible woody fibers. It is not a silly sentimental illusion to believe that the taste of fresh vegetables is very different from that of vegetables left sitting in the pantry.

Cold preserves this taste of freshness, slowing decomposition and preventing degradation by microorganisms. Why? First, because plant cells live more slowly in the cold than at the ambient temperature, biochemical reactions take place more slowly. Microorganisms are slowed down as well, so they proliferate less and degrade vegetables to a lesser degree.

On the other hand, fruits and vegetables cannot stand the cold at all. Certain tropical vegetables in particular are especially sensitive to it. Bananas, for example, are damaged by their enzymes, which brown the banana skin. Avocadoes darken and do not ripen at temperatures below 7C (44F). Lemons and other citrus fruits get spots. Pineapples, melons, tomatoes, cuc.u.mbers, and green peppers keep better at 10C (50F) than at lower temperatures. Potatoes get soft at temperatures below 4C (39F) because the starch in them continues to turn into sugar. Most other vegetables-carrots, cabbage, greens, and so on-keep well at about 0C (32F). Their cells contain salts that prevent freezing according to the same phenomenon that lowers to -17C (1F) the temperature of a mixture of ice and salt.

The Big Chill Freezing completely halts respiratory reactions in vegetables, but it kills plant tissue. Water in the cells forms ice crystals that pierce the plant cell walls and membranes. During the freezing process, vegetables wilt because the broken walls and membranes no longer keep the cellular ma.s.s rigid. To avoid this inconvenience, the cooling must take place as quickly as possible. In that way, the ice crystals that appear remain small and numerous.

One more precaution: freezing considerably reduces enzyme and chemical activities, but it does not block them completely. The only way to terminate all activity is to blanche the food product. Quick immersion in boiling water inactivates the enzymes; subsequent immersion in cold water stops the cooking process and weakens the cell walls.

Fruits, however, are rarely blanched, because blanching makes them lose their flavors and textures. The enzyme action that turns fruit brown is better prevented with the help of a sugar, alcohol, or an as...o...b..c acid solution.

Vinegar The Acid of Alcohol Since Louis Pasteur's time, we have known that vinegar is formed through the fermentation of ethylic alcohol by a single-cell fungus related to yeast, Mycoderma aceti Mycoderma aceti. In conditions of limited acidity, with certain concentrations of alcohol, and in the presence of nutritive compounds such as the proteins present in wine, these mycoderms develop and form a grayish veil, sometime as fine as silk, sometime more solid.

The fungus absorbs oxygen from the air and fixes it on the alcohol, transforming the alcohol into acetic acid, which, as a solution in water, const.i.tutes vinegar.

Mycoderms like acid products and develop better if the environment is initially a bit acid. To make vinegar, adding a bit of already formed vinegar to the wine to be transformed is recommended. This addition has the advantage of preventing the wine from being colonized by the "flower of wine," another microorganism that prompts wine to spoil.

Must You Have a Mother to Make Vinegar?

Often recommended as an aid in making vinegar, mother of vinegar is composed of acetic mycoderms that have not penetrated the ma.s.s of vinegar ... and that therefore act in a harmful fas.h.i.+on. Instead of transforming wine into vinegar, they destroy it, consuming the oxygen in it, because, in solution, it lacks them.

What is worse, mother of vinegar destroys the odorant compounds that give vinegar its odor. The conclusion is incontestable. When making vinegar, avoiding mother of vinegar is absolutely necessary. Only the surface veil is beneficial.

Vinegar is produced in various ways, but the Orleanais method is done with the help of a row of casks. Wine is regularly added to the highest cask, and vinegar simultaneously decanted from the lowest cask. More precisely, to make 230 liters (around 243 quarts) of vinegar, 8 to 10 liters (around 8.5 to 10.5 quarts) are decanted each week, replaced by an equal amount of wine. The operation must take place in a half-full container, so that there is maximal exposure to air. The temperature must be consistent, and the veil (which forms spontaneously) must not be damaged by the addition of wine.

Vinegar can be made with various fruits, raisins, honey diluted with water, cider, fermented pear juice, berries.... But the best vinegar is made with good wine. And, as everyone knows, aromatic vinegars can also be made with various herbs, such as tarragon.

Let us also note that balsamic vinegar, made in the Modena region of Italy, is the only vinegar that harmonizes with the wine served during a meal. This vinegar is produced beginning with white grapes and sugar. After harvesting, and with the first signs of fermentation, the must is drawn from the vats, filtered, and slowly boiled. Then it is filtered once again and pa.s.sed from smaller to smaller casks while the acetification takes place and the liquid becomes concentrated. Try it with walnut oil to accompany a salad garnished with sliced truffles! It is more expensive than standard vinegar, but what a pleasure not to ruin the taste of the wine when you eat your salad.

Kitchen Utensils How Can We Rejuvenate Silverware?

Silver place settings, the treasures of our grandmothers, ornaments to our tables, a pleasure to the eye, have a serious inconvenience. They tarnish. If they come in contact with egg? Their radiance seems irremediably lost. If they are washed in a sink that contains less n.o.ble metals? They darken as if they were too fine to endure contact with commoners.

How to recover them? The solution is simple. Remedies abound, but some are not reliable. I offer you here my full a.s.surance of the perfect effectiveness of the following two remedies.

The first possibility involves the use of hydrogen peroxide. Actually, silver turns dark only because it is oxidized, generally by sulfur. Abundant in eggs, sulfur binds to silver in an insoluble compound of silver sulfide. Hydrogen peroxide continues the oxidation, transforming the insoluble sulfur into soluble silver sulfate. Consequently, this remedy should be reserved for solid silver place settings only.

A second possibility, hardly more complex, is effective for silver-plated settings. The sulfur can be dissociated by electrolysis, and the silver plating can thus be preserved.

To do this, cover the bottom of a plastic container with aluminum foil. Add hot water and a tablespoon of cooking salt. Then place the tarnished objects in the container is such a way that they are in contact with the aluminum. Thanks to an electrical circuit composed of the conducting solution (salt serves to make the water a conductor), the aluminum, and the silver, the following chemical reaction takes place. The aluminum loses electrons, which flow to the metallic silver. On the surface of the place settings, the silver bound with sulfur captures these electrons, recovering its metal form, while the sulfur is released into the solution, migrates toward the aluminum, and forms aluminum sulfide.

You can speed up the process by using water that is almost scalding.

Why Beat Egg Whites in Copper Bowls?

Is it necessary to use copper bowls when beating egg whites into stiff peaks? Copper is said to make egg whites stiffer than other materials do, and furthermore one of the plates in Alembert and Diderot's Encyclopedia Encyclopedia depicts, in an ill.u.s.tration of a kitchen, a copper bowl for beating egg whites. depicts, in an ill.u.s.tration of a kitchen, a copper bowl for beating egg whites.

Scientifically, the jury is still out. Apparently, egg whites beaten in a copper bowl are stiffer than those beaten in other containers, but what is the reason for that?

The "cul-de-poule," that hemispheric copper bowl reserved for beating egg whites in large kitchens, has the advantage of never coming in contact with fat, which, as we have seen, inhibits the bonds between the egg white proteins. It could be the perfect cleanliness of these bowls that produces those perfectly beaten egg whites.

The significance of the copper has been tested since the beginning of the century, when it was observed that one egg white protein, conalb.u.min, bonded to metallic ions and thus became much more resistant to denaturation. It was then a.s.sumed that if the conalb.u.min bonded to the copper in the bowl where it was beaten, overbeating would become more difficult. It has been verified that conalb.u.min does bond to copper (the color of egg whites beaten in copper is different from that of whites beaten in iron, for example, because the conalb.u.min-copper and the conalb.u.min-iron complexes have different light absorption properties), but many studies must still be done to confirm that the sequestering of metals is really responsible for stabilizing egg whites. And even with this hypothesis, it has not been established that egg whites beaten in copper withstand cooking better; nothing replaces experimentation.

Nevertheless, let us mention that copper must be handled with caution. It is so toxic that water placed in copper and left in the open air is not colonized by ambient microorganisms. Moreover, what matters most of all is the perfect cleanliness of the container. The presence of fat, as we have seen with regard to souffles, interferes in forming stiff peaks. If you have any doubt and suspect that fat is present, clean the bowl by rubbing it with salt and vinegar or with a lemon quarter.

Why Cook in Copper Saucepans?

Copper saucepans seem like a luxury. Are they really? That is not clear, because copper conducts heat very well. In any one spot in the pan, all the excess heat is rapidly dissipated because the heat spreads quickly into the rest of the utensil. Thus a copper pot reacts very rapidly to variations in temperature, which ensures cooking by the entire surface of the pan, bottom and sides, without "hot spots," points that overheat and trap molecules, carbonize them, and give the dish a burnt taste. With copper, it seems that the temperature is better controlled, that it can be adjusted at will, without too much lag. This trait is indispensable for the most delicate sauces and for slowly simmered dishes.

To avoid the toxic contact of verdigris, copper utensils must be coated with pure tin, done nowadays by electrolysis. This tinplate must be renewed regularly. Bowls for beating egg whites and sabayon saucepans are not coated, however, because whisks sc.r.a.pe the tin, which is quite a soft metal. Also, too much heat must be avoided with tinplated utensils to avoid melting the tin.

Why do I have a few misgivings about praising the physical nature of copper to you? Because, as a chemist, I suspect the state of the surface of the material your saucepan is made out of matters more than the nature of the metal itself. A porous copper would no doubt be disastrous. There are studies in progress....

It remains a fact that copper is beautiful. And expensive as well. It can very adequately be replaced by another heat-conducting metal like aluminum, but the aluminum must be thick enough to prevent burning.

Why Use Wooden Spoons?

Wooden spoons are present in all kitchens. They benefit from the current taste for natural products, but they truly do deserve their place because they do not conduct heat. Left in a preparation that is cooking, they can be handled without burning the fingers of the cook. What a blessing that this tool, and the material of which it is made, wood, does not scratch the tin that lines the inside of our copper saucepans!

Mysteries of the Kitchen Unanswered Questions In this exploration of the wonderful world of the gourmand, we have had the opportunity to discover some answers. Nevertheless, cooking is teeming with questions. It is my dream that science will help us to answer them.

Here are just a few: Supposedly, a sabayon can boil without turning if a pinch of flour is added to the mixture of egg yolk beaten into a liquid (water, wine, juice... ). Experience shows that this precaution is effective. How does the flour act to protect the sauce?If egg yolk is added to coa.r.s.e sugar without being worked in, it cannot later be incorporated into the cream or the dough with which we want to mix it. The egg yolk "burns." Why is that?When preparing a stock or a brown sauce, the ingredients are boiled for a long time in water. Which components escape with the water vapor (we smell them) and in what proportion? Which remain? How to influence this distribution?Can a mixture of oil and b.u.t.ter be heated to a higher temperature than b.u.t.ter alone?It is said that, when preparing a sauce, liquid can only be added to a roux when the saucepan is away from the heat. Why?Apple juice turns dark. How can that be avoided?Why does bouillon prepared in a saucepan covered with a lid become cloudy, and why must it be brought to a boil slowly?Why is parsley used in short-term marinades (a day or two) but not recommended for longer ones?Is it true that a suckling pig served at the table must have its head cut off immediately, or its skin will not be tender?Why does excessive kneading make pie dough rubbery?Why does a puree become rubbery if it is overworked or if it is worked at either too hot or too cold a temperature?Why does adding a small quant.i.ty of liquid to mayonnaise whiten it as well as making it more fluid?When preparing jam, does the kind of metal the saucepan is made out of matter?Is it true that champagne will not make bubbles in gla.s.ses that are washed in a dishwasher?If a little spoon is placed in the neck of an open champagne bottle, does that keep bubbles from escaping? If so, why?Is it true that you can avoid releasing too many bubbles by first pouring a small amount of champagne into a gla.s.s before filling it completely?Does the speed with which a marinade soaks into meat depend on the type of meat it is?Can you make a successful aioli without egg yolks, using just garlic and oil?Why does gelatin added to boiling milk make it turn?

Do you know the answers to these questions? If you would like to share them with me, I would be much obliged. Do you have other questions? Let me know what they are. I will try to find the answers.

And, in the meantime, bon appet.i.t bon appet.i.t!

Glossary

A.

AAAH!: The cry of delight guests utter when the first dish arrives. The sleight of hand responsible for the most beautiful "aaahs" cannot be explained in terms of physical chemistry.

ACETIC ACID: The main acid compound of vinegar.

ACID: Any substance that gives the impression of acidity; for chemists, these are molecules that, in solution, release hydrogen ions (H+; hydrogen atoms that have lost their single electron). In cooking, the princ.i.p.al acid solutions are lemon juice and vinegar.

ACIDITY: A sensation communicated by substances like vinegar or lemon juice. Acidity is measured on the pH scale, from 0 to 14. Solutions with a pH lower than 7 are acid; solutions with a pH higher than 7 are basic.

ACTIN: One of the princ.i.p.al proteins in muscles, responsible for muscle contraction. When meat is cooked, the actin coagulates.

ALb.u.mINS: Small proteins soluble in water. Ovalb.u.min is one of these, present in egg whites, for example. In blood, there is serum alb.u.min. The word "alb.u.min" is generally used incorrectly in cookbooks, where it really means protein, a word that replaced "alb.u.min" in chemistry about a century ago.

ALCOHOL: Any organic molecule with a carbon atom bound to an oxygen atom that is then bound to a hydrogen atom (-C-O-H). The most common alcohol, the one in wine, brandy, and liqueurs, is ethyl alcohol, with the formula CH3CH2OH.

AMINO ACIDS: In binding together like links in a chain, these molecules form proteins. The molecules of amino acids are characterized by the presence of a carbon atom to which are bound especially an acid group COOH (the letter C represents the carbon atom, O the oxygen atom, and H the hydrogen atom) and an amino group NH2 (with a nitrogen atom [N], bound to two hydrogen atoms). Plant and animal organisms contain twenty types of amino acids. (with a nitrogen atom [N], bound to two hydrogen atoms). Plant and animal organisms contain twenty types of amino acids.

AMYLASE: An enzyme that breaks down starch molecules.

AMYLOPECTIN: This is a polymer, that is, a molecule formed by the linking of many small identical molecules. The links in amylopectin are glucose molecules. The molecule is branched and insoluble in cold water.

AMYLOSE: Like amylopectin, but this polymer is in straight chains and soluble.

ASPARTAME: This is a sweetener, that is, a compound with a sweet taste. It dissociates in heat, releasing phenylalanine, which is bitter.

ATOM: A structure cla.s.sically represented in the form of a nucleus around which rotate electrons. The nucleus is composed of protons, particles with a positive electrical charge, and neutrons, which are neutral. Having a negative electrical charge, the electrons are generally retained close to the nucleus by the forces of electrical attraction that are exerted between opposite charges.

AUTOXIDATION: A chemical reaction that produces rancidity in fats. It takes place rapidly in the presence of oxygen.

B.

BeARNAISE: One of the crown jewels of French cooking (I have a weakness for it; don't tell my wife!). A sauce composed of melted b.u.t.ter emulsified (see Emulsion) in a reduction of white wine, shallots, and vinegar. Egg yolks provide surface-active molecules for this emulsion, and their proteins coagulate, making microscopic lumps. Indeed, a successful bearnaise is a failure, microscopically. Emulsion) in a reduction of white wine, shallots, and vinegar. Egg yolks provide surface-active molecules for this emulsion, and their proteins coagulate, making microscopic lumps. Indeed, a successful bearnaise is a failure, microscopically.

BeCHAMEL: A cla.s.sic sauce made by diluting a roux (which see) with milk or bouillon.

BEURRE BLANC: Literally, "white b.u.t.ter"; a delicious sauce with fish. This is an emulsion obtained by stirring b.u.t.ter into a small quant.i.ty of liquid. It is a good idea to begin with cream.

BEURRE MANIe: Literally, "handled b.u.t.ter"; cold b.u.t.ter kneaded with flour, used as a thickener. Added to a sauce that is too thin, it provides the necessary viscosity. It is a stopgap measure, because the taste of raw flour is objectionable to true gastronomes.

BINDING: Or "thickening"; an operation meant to increase the viscosity of a sauce.

BISCUIT: Literally, "cooked twice"; "biscuit" is the French name for a sponge cake, different from a genoise sponge cake in that the egg whites are beaten into stiff peaks separately from the egg yolks and sugar.

BRAISING: A very gentle cooking process that enhances the taste of meat. A cla.s.sic braising procedure consists of two stages: browning the meat by pa.s.sing it through a very hot oven in order to "caramelize" the surface; then long cooking at temperatures lower than 100C (212F) to tenderize the meat without drying it out. Putting strips of meat, bacon, or ham around the meat that is being braised prevents the loss of juices.

BRINE: A solution containing more salt than can be dissolved in it. It is used in cooking for extracting through osmosis (which see) the water from plant and animal cells and thus preventing the proliferation of microorganisms.

b.u.t.tER: Obtained by churning cream, this is an emulsion composed of small water droplets dispersed in milk fat. When you stir preparations that contains milk or cream, like mixtures for mousse, mousseline, or whipped cream, be careful to cool them in order to prevent them from turning into b.u.t.ter through cooling.

C.

CAPILLARITY: Through the action of capillarity, water is introduced into very small s.p.a.ces, like the interstices between starch granules in flour.

CASEIN: Eighty-five percent of the proteins in milk are casein. Casein molecules aggregate when the milk becomes acid or too salty: the milk curdles.

CATALYST: A molecule that prompts a chemical reaction.

CELLS: Vegetables, meats, the human organism-all are composed of billions of cells, microscopic sacks, each enclosing a structure called a nucleus, in a complex aqueous environment, the cytoplasm. All living cells are confined by a membrane. In addition, plant cells are protected by a rigid wall.

CHEMICAL REACTION: The process by which many molecules that encounter one another can exchange atoms and be rearranged.

CHEMISTRY: Among the most beautiful of the sciences, the one dealing with molecules as they react. Scientists often say of chemistry, "It's just cooking." What an honor!

CHOLESTEROL: This is a lipid (which see). It is accused of all sorts of evils because of the risk of coronaries when the blood contains too much of it, but the cholesterol in our food is not the direct source of blood cholesterol.

CLARIFY: This is to give limpidity and transparency to bouillon, a sauce, and the like.

COAGULATION: An aggregation of proteins provoked by heating or acidification, for example.

COLLAGEN: Collagen molecules form sheaths around the muscle cells in meat. Collagen is responsible for meat's toughness. When it is broken down, by heat in the presence of water, gelatin results.

COLLOID: A dispersion of solid, liquid, or gaseous particles in a continuous phase, either solid, liquid, or gas. Sauces obtained by diluting a roux (which see) in a liquid, milk or bouillon, are colloids.