Part 2 (1/2)
Lemon juice or vinegar adds water to the already const.i.tuted emulsion. The droplets have more s.p.a.ce into which to flow. The mayonnaise is more fluid. Simultaneously, it turns whiter. Perhaps the droplets are dispersing the light differently, resulting in this effect, but that remains to be proven.
How Much Mayonnaise Can Be Prepared with a Single Egg Yolk?
The amount of mayonnaise that can be made with a single egg yolk depends on the quant.i.ty of water present. Traditional recipes generally indicate that if there is too much oil for the quant.i.ty of yolk used, the sauce decomposes. They recommend using, at the most, one to two deciliters (3.38 to 6.76 ounces) of oil per egg yolk.
Nevertheless, my American friend Harold McGee, author of the very popular book On Food and Cooking On Food and Cooking (Scribner and Sons), has prepared up to twenty-four liters (25.37 quarts) of mayonnaise with a single egg yolk. Naturally, he had the aid of science. Knowing that oil arranges itself into droplets in a continuous phase of water, he figured that the small quant.i.ty of water normally contributed by the egg yolk (about a half teaspoon per yolk) was not enough to prepare a large emulsion. Thus, to maintain the separated oil droplets in the aqueous phase, he added water as he added oil. More precisely, for each cup of oil, he advises adding two or three teaspoons of water. (Scribner and Sons), has prepared up to twenty-four liters (25.37 quarts) of mayonnaise with a single egg yolk. Naturally, he had the aid of science. Knowing that oil arranges itself into droplets in a continuous phase of water, he figured that the small quant.i.ty of water normally contributed by the egg yolk (about a half teaspoon per yolk) was not enough to prepare a large emulsion. Thus, to maintain the separated oil droplets in the aqueous phase, he added water as he added oil. More precisely, for each cup of oil, he advises adding two or three teaspoons of water.20 Since a large egg yolk contains enough surface-active molecules to emulsify many quarts of mayonnaise and since too much egg yolk gives the mayonnaise a taste of raw egg that some find disagreeable, I suggest that, when you wish to prepare a small quant.i.ty of mayonnaise, you do not use the whole yolk-a drop is enough to make a big bowl of mayonnaise-and you begin the sauce with lemon, vinegar, or plain water, adding a few finely chopped herbs for flavor.
Why Must Mayonnaise Be Beaten Vigorously?
It is necessary to break up the oil into little droplets and make them migrate in the water, carrying the surfactants.21 Now, the lower the temperature, the greater the difference between the miscibility of the water and oil. If you congeal the oil by cooling it too much, you will no longer be able to divide it into droplets. For the same reason, you must warm the b.u.t.ter used in preparing a bearnaise or a hollandaise sauce, two other emulsions in which the egg, again, provides the surfactants. Now, the lower the temperature, the greater the difference between the miscibility of the water and oil. If you congeal the oil by cooling it too much, you will no longer be able to divide it into droplets. For the same reason, you must warm the b.u.t.ter used in preparing a bearnaise or a hollandaise sauce, two other emulsions in which the egg, again, provides the surfactants.
Why Can't the Oil Be Poured In All at Once?
Cla.s.sically, recipes indicate that the vinegar (please, no mustard, otherwise your mayonnaise is no longer a mayonnaise: it is a ”remoulade”) must be mixed first, then the egg yolk, and finally the oil must be added, slowly, while whisking vigorously. Why add the oil to the aqueous phase, rather than the other way around? First, because it is necessary to separate the oil into microscopic droplets, which is much easier if one begins with a drop of oil in water, rather than vice versa. Second, because the surface-active molecules coat the drops of oil most quickly and consistently if the surfactant is initially present in large proportions (it is initially present in the form of micelles, spheres at the center of which all the hydrophobic tails of surface-active molecules have gathered).
The first task is to produce small, well-separated drops. As long as there is more water than oil, large drops can escape the action of the whisk, and oil rises to the surface. When the volume of incorporated oil is equal to the initial volume of water and seasonings, the drops mutually prevent one another from rising, and the emulsion begins to stabilize. Then, as one continues to add oil, the small drops serve to break up the big ones, impeding their flow.
Why Does Mayonnaise Curdle?
Mayonnaise turns because it flocculates: the oil droplets merge with one another and separate from the aqueous phase. Generally, this catastrophe takes place either because the ingredients are too cold or because the emulsion does not contain enough water for the quant.i.ty of oil added.
To salvage mayonnaise that has curdled, cookbooks recommend adding another egg yolk, as if the problem were caused by the oil. But it is sometimes enough to add water and beat vigorously. You'll save an egg, but you'll need elbow grease. A better solution is to wait until the oil and water separate. Pour off the oil, and then add it back drop by drop, whipping continuously: all the useful molecules were present but not in the right configuration; you only have to rearrange them.
The Egg's Incarnations Essential Accessories The egg is the unrecognized star of cooking. In his Almanach des gourmands Almanach des gourmands, Grimod de la Reyniere celebrated it in these terms: ”The egg is to cooking as the articles are to speech, that is to say, such an indispensable necessity that the most skillful cook will renounce his art if he is forbidden to use them.”
How true! Its whites, beaten into stiff peaks, merit their own chapter. Souffles, which they cause to rise, require the examination of so many principles of physics that, again, a complete chapter will be necessary if we are to master them. And the hard-boiled egg, though its preparation seems within the range of the least skilled novice, requires much care to be truly good.
Nevertheless, the importance of eggs in cooking is often underestimated. First of all, the egg is indispensable anytime you want to give a dish a specific form. You break an egg, whole or not, into a container that is then heated. The egg, possibly with some filling, takes the form of the container and retains it after being cooked.
Second, when its whites are beaten into stiff peaks, the egg provides the foamy element in recipes for meringues and souffles, in mousses that are cooked, and also in recipes for the various chocolate or Grand Marnier mousses that are served cold and not cooked.
Next, eggs can form permanent gels that trap solid elements, as in, for example, clafoutis (a type of fruit tart) or quiche.
Finally, the egg is used for its surface-active compounds in various sauces: mayonnaise, bearnaise, hollandaise, gravy, and so on.22 In all these uses, the egg is an accessory ... an essential accessory. In all these uses, the egg is an accessory ... an essential accessory.
In other dishes, the egg is not just an accessory but a princ.i.p.al player: think of boiled eggs, omelets, and eggs mimosa, for example.
Why is it so versatile? First of all, the yolk is about half water, one-third lipids (lecithin and cholesterol among them), and 15 percent proteins. The white, on the other hand, is nearly all water, since it contains only 10 percent proteins (primarily ovalb.u.min and conalb.u.min).
How does knowledge of this composition serve us? It lets us answer all the following questions.
How Can You Tell a Raw Egg from a Cooked Egg?
In a refrigerator shared by an entire family, cooked eggs are frequently mixed up with raw ones. They have the same ma.s.s (weigh them to convince yourself of this), the same color, the same surface appearance. How to distinguish them?
When in doubt, remember that a raw egg is a viscous liquid. If you make it spin, you turn only the sh.e.l.l. The inside of the egg remains semi-immobile, exactly like coffee when one turns the cup. Because of the friction between the liquid and the sh.e.l.l, a raw egg quickly loses speed, while inside the liquid slowly begins to move. A raw egg spins with difficulty and then, released, slows down. On the other hand, a hard-cooked egg, all of a piece like a spinning top, turns easily and for a long time as soon as it is set in motion. If you have no egg available for comparison, spin your mystery egg and then stop it by just touching and releasing it. A cooked egg will remain still. A raw egg will continue to spin when released because of the motion of the egg white within the sh.e.l.l.
Why Does an Egg Cook?
Let us consider the simple case of the fried egg. A priori, cooking an egg is a complex operation. Think about it: all those different molecules! Nevertheless, an examination of the egg's composition shows us that what we have here, at a first approximation, is only a mixture of proteins and water.
The water behaves as expected. When it is heated, its temperature increases steadily until, at 100C (212F), it boils, forming bubbles.
On the other hand, the proteins are molecules a.n.a.logous to long strings, often folded back on themselves because of forces that come into play between the atoms of a single molecule. When they are heated, these weak forces are broken, and since each broken bond leaves two atoms hard-pressed for companions, the heating encourages encounters between the forsaken ones, which can thus form bonds even if they do not belong to the same molecule. Moreover, some particular parts of proteins, made of one sulfur atom and one hydrogen atom, can link when the proteins are denatured. They make specific bonds called disulfide bridges responsible for coagulation.
Thus, when an egg's temperature increases, the b.a.l.l.s of string that are the proteins begin to form chains without unwinding significantly. The liquid turns solid, but the various kinds of proteins do not all coagulate at the same temperature. One forms a network at 61C (141F), another at 70C (158F), and so on. For each temperature, there is a specific culinary result, and the higher the temperature reached, the harder the egg, because the greater the number of protein networks that trap water molecules. In the end, when all proteins are coagulated and the water is lost, the egg white becomes rubbery.
Moral: When you are frying an egg, stop cooking it as soon as it turns opaque. Beyond that point, your egg will no longer be worth its salt.
Why Does the Egg Yolk Cook More Slowly than the White?
Cooks know that the yolk of an egg, fried or soft-boiled, cooks much more slowly than the white. This is partly because the major proteins in the yolks coagulate at a temperature seven degrees higher than that at which those in the whites coagulate. To complicate matters further, when boiling eggs, the white protects the yolk, causing its temperature to rise more slowly.
The famous three-minute recommendation for cooking soft-boiled eggs corresponds to the time during which the temperature increases in the various parts of an egg immersed in boiling water. After three minutes, the outside reaches 100C (212F) and the core reaches about 70C (158F), depending on the size of the egg. It takes a minute longer for the temperature of the egg yolk to rise the seven degrees necessary for its coagulation.
We must now ask, why not bake eggs in a 65C (149F) oven for an extended period of time (slightly more than an hour for a 60-gram egg [just over two ounces]), rather than remaining at the mercy of an egg timer? We would be sure of a perfectly cooked egg white and a perfectly runny yolk, with no risk of failure!
Why Won't the Egg White Closest to the Yolk Cook?
Anyone who has fried an egg has encountered this phenomenon: surrounding the yolk, part of the egg white refuses to coagulate.
That is because the protein in the egg white called ovomucin coagulates with more difficulty than the other proteins; this is what gives the egg white in contact with the yolk its viscosity.
How to get it to cook without letting the rest of the egg white become rubbery (see the question ”Why Does an Egg Cook?”)?
Salt and acids (vinegar, lemon juice, etc.) promote the cooking of a solution of proteins in water because their electrically charged atoms, or ions, come to surround the atoms possessing the complementary electrical charge in the proteins. These similar electrical charges are normally responsible for the winding and dispersing of the proteins. In the presence of complementary ions, the proteins can unwind, come together, and form bonds more easily. In other words, the proteins cook at a lower temperature in the presence of salt or acids. When cooking a fried egg, you can obtain a h.o.m.ogeneous white by salting the white around the yolk.
In the extreme, you can almost cook an egg by immersing it in vinegar, without heating it. The acid's ions prompt the weak bonds to break, so that the abandoned atoms can combine with the abandoned atoms of other molecules. The egg coagulates. This explanation also answers the following question.
Why Add Vinegar to the Water When Poaching an Egg?
Adding vinegar to the cooking water when poaching an egg accelerates the coagulation of the part of the egg that is in contact with the boiling solution. The outside part of the egg coagulates immediately, constraining the rest of the egg, which can thus form a ma.s.s without dispersing into the solution. Salt is said to do the same, but experimenting will prove vinegar's superior effectiveness.
Likewise, there is an advantage to adding a little vinegar to the water used for soft-boiling eggs. If the sh.e.l.l cracks, the egg white coagulates immediately, sealing the leak (another solution for avoiding cracks is to make a small pin hole in each end of the egg; in that way, the air that expands does not break the egg and escapes without causing damage).
The Odorous Mysteries of the Hard-Cooked Egg Those who know how to cook sometimes forget this: you can can cook a hard-boiled egg badly! cook a hard-boiled egg badly!
Let us turn to Madame Saint-Ange, author of a long-standing cooking column whose excellent advice was collected in book form by Larousse in 1927: It is a very common mistake to think that there is no risk of overcooking when it is a matter of hard-boiled eggs and that therefore it does not matter how long they remain in the boiling water after they have become hard. An overcooked hard-boiled egg is tough; the yolk is rimmed with green, the white gives off an unpleasant odor, and the whole thing gives the impression of an egg that is not fresh.Another mistake: putting eggs in lukewarm or even cold water, and only then bringing it to a boil. The result is a faulty distribution of the white around the yolk, not achieving an attractive roundness or, in the case of stuffed eggs, attractive white cups of a regular thickness.
The consequences of the first mistake are simple to explain. When eggs are cooked too long, the egg's proteins, which contain sulfur atoms, release a gas called dihydrogen sulfide, the infamous odor of rotten eggs. This gas reacts with iron ions present in the egg's ovotranferrin (iron-carrying) proteins and thus gives it its greenish color.
To cook hard-boiled eggs properly, immerse them in water that is already boiling, allow the water to return to a boil, and let the eggs cook for ten minutes. Then put the eggs immediately into cold water. That will make them easier to sh.e.l.l. And again, if you want to be really modern, bake your eggs in a well-moderated oven, set at any temperature you choose, depending on how well done you like your eggs.