Molecular Gastronomy: Exploring the Science of Flavor (43 page)

drain off the upper oily phase into another container, reserving the watery

solution at the bottom.

How can these fragrant solutions be put to good use? If you were to prepare

the cepe-scented water using egg whites instead of water, you could incorpo-

rate the cepe-scented oil by whisking it into the egg mixture. The egg proteins

will then be tensioactive molecules, which will give you a cepe emulsion.

In Praise of Fats
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88

Mayonnaises

The art of mixing oil with water.

m a y o n n a i s e i s a r e m a r k a b l e s a u c e : Through the miraculous in-

tervention of the egg yolk, cooks manage to combine oil and water. Let’s try

our hand at making a few new varieties that preserve the spirit of traditional

recipes while enriching our culinary arsenal.

What happens when one adds oil to a mixture of vinegar, mustard, egg yolk,

and salt? To the naked eye the preparation is homogeneous, but a microscope

shows that the ingredients are not thoroughly mixed together: Large oil drop-

lets are dispersed in the small amount of water contributed by the vinegar,

mustard (which is itself made with vinegar), and egg yolk. If the oil doesn’t

float on top but emulsifies instead, this is because the yolk’s tensioactive mol-

ecules (one part of which is water soluble and the other fat soluble) coat the

oil droplets, with the water-soluble part immersing itself in the water and the

other part immersing itself in the oil. In egg yolks these molecules are primar-

ily proteins and, in smaller proportion, lecithins.

Draped over the droplets of oil in this fashion, the tensioactive molecules

prevent them from aggregating. These molecules cannot be seen under the

microscope. Nor can the vinegar or the salt, which nonetheless play an im-

portant role, enabling the tensioactive molecules of the yolk to bring about

an electrical repulsion between the oil droplets and thus helping to stabilize

the sauce.

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How much mayonnaise can be made from a single egg yolk? The amount

of oil that can be added depends on two things: the quantity of water in which

the oil droplets are distributed and the quantity of tensioactive molecules. A

simple calculation shows that there are enough tensioactive molecules in a

single egg yolk to make several liters of sauce if there is enough water because

the oil content can be as high as 95%.

Why do mayonnaises go wrong when no more than a large bowlful has

been made from one yolk? Because the oil droplets are so tightly packed to-

gether that they have trouble moving, and the sauce becomes firm. At this

point, in order to prevent the sauce from breaking, it is necessary to add more

water before adding more oil. In the case of homemade mayonnaise, by the

way, use only a single drop of egg yolk. This is enough to coat all the droplets

in your sauce.

A Yolkless Mayonnaise

Let’s take matters a step further and do away with the egg yolk altogether.

Once it is understood that a mayonnaise is an emulsion, which is to say a

dispersion of oil droplets in water, one can experiment by modifying the in-

gredients. We may begin by replacing one set of tensioactive molecules with

another. This type of molecule is found in many foods. The reason egg whites

can be stiffened by whisking, for example, is that they are a solution of proteins

that coat air bubbles.

Take an egg white and add to it a drop of vinegar, a little salt, and a little

pepper. Now—slowly at first and then more rapidly—add oil while constantly

whisking the mixture. A small amount of foam begins to form and then sub-

sides as the oil is incorporated, exactly as in a mayonnaise. After having intro-

duced a large quantity of oil, you have a yolkless mayonnaise.

An Eggless Mayonnaise

Can we push this idea still further? There is no particular reason to rely on

the tensioactive molecules of an egg to give body to a mayonnaise. Why not use

gelatin, for example? Its tensioactive properties are well known empirically to

cooks, who use it to thicken a number of warm sauces. Let’s melt some veal

Mayonnaises
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demi-glace (any highly gelatinous solution will do), add to it a bit of vinegar, a

bit of salt if you like, and a bit of pepper, and whisk in the oil. Once again, the

oil is very readily incorporated and forms what can be seen under the micro-

scope to be an emulsion.

Is the result worthy of the name “mayonnaise”? To answer this question

one has to decide exactly what a mayonnaise is. If it is a cold emulsion of

oil in water, then these three preparations are all mayonnaises. If the taste of

egg yolk is the thing that matters, then only the classic mayonnaise can legiti-

mately be called by this name; indeed, there is a law in France that an emulsion

can be called mayonnaise only if it contains more than 8% yolk. Recipes for

mayonnaise vary widely, however. The great Antonin Carême, known in the

nineteenth century as the Napoleon of the stoves (a compliment at the time),

made his mayonnaise without mustard, using only olive oil from Aix, which

he added with a wooden spoon. Other cooks swore by mustard. All tastes are

in nature, after all.

The fact remains that an eggless mayonnaise, as we may provisionally call

it, increases culinary freedom. Using mint jelly, for example, one may create

a mint mayonnaise to accompany a traditional English leg of lamb. But one

can also thicken a mayonnaise with various aromatic solutions—a rich lobster

stock, for example, or an infusion of rosemary, thyme, and orange juice—to

which gelatin has been added, either in powdered form or in leaves.

296 | a c uisine f or t omor r ow

89

Aioli Generalized

Delicious emulsions that can be made from any vegetable, meat, or sh.

w e s t a r t w i t h a i o l i — the real article made in Provence by adding olive

oil to crushed garlic, without the benefit of egg yolk. It is an emulsion, which

is to say a dispersion of oil droplets in water, supplied in this case by the gar-

lic. Why should this sauce be stable, whereas normally a mixture of oil and

water separates? Because garlic contains tensioactive molecules that coat the

oil droplets and prevent them from fusing. Aioli is a relative of mayonnaise,

in which the protein molecules and phospholipid lecithins of the egg yolk are

tensioactive.

Let’s try varying the traditional recipe a bit. Does the shallot, which belongs

to the same vegetable family as garlic, also contain tensioactive molecules that

permit us to make an “échalatoli”? Can an “oignoli” be made from onions? The

experimental response is conclusive: Adding oil to crushed shallots or onions

does in fact yield such emulsions. In the worst case it is necessary to add a

little water (just as, in certain recipes for aioli, adding a piece of bread soaked

in milk is recommended). It remains for cooks to dream up new dishes that

these sauces could accompany.

But are there vegetables other than the ones of the lily family that could

serve the same purpose? After all, cooks know that mustard can be used to

make emulsioned vinaigrettes, for mustard also contains tensioactive mole-

cules that help to stabilize the sauce.

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The Virtues of Membranes

The answer is simple if we recall that all cells, whether plant or animal,

contain compartments of water and proteins that are bounded by membranes.

These membranes are composed of phospholipid molecules having a water-

insoluble lipidic tail and a water-soluble head. In living cells these phospho-

lipid molecules form double layers because the hydrophobic tails are grouped

together inside the various cellular compartments, whereas their hydrophilic

heads
are in contact with the water outside the compartments. Phospholipid

molecules are abundant and have strong tensioactive properties. Can they be

used to thicken an emulsion?

Let’s try crushing a zucchini and adding oil to it, drop by drop. The result

is a thick sauce that, by analogy once again, we may call “courgettoli.” Why

not move on next from the plant to the animal kingdom, because animal cells

also contain membranes? If we crush a cube of beef and add some oil, we find

that we obtain “bœufoli.” From any vegetable or animal, then, we discover that

we can make an emulsified sauce as long as we release the phospholipid mol-

ecules, for example by crushing them and adding oil (again, a bit of water must

be added at the outset if the chosen ingredients contain too little of it).

Phospholipids are not the only tensioactive molecules in plant and animal

cells; many proteins have good emulsifying properties as well. Whisking oil

into an egg white forms a remarkably stable emulsion but with very little flavor.

More interesting sauces can be made from meat, fish, and vegetables, whose

protein molecules likewise contribute to their stability.

New Mousses

From emulsions we turn now to an analogous physical system, foams, which

consist of air bubbles dispersed in a liquid or solid. The fact that a chocolate

mousse can be obtained by whisking a chocolate emulsion, as we shall see later

in this section, suggests that it may be possible to generalize this procedure.

We might try using cheese, for example. Cheese contains a great amount

of fat and tensioactive molecules, or caseins, which disperse the fatty droplets

throughout the milk. To produce a cheese mousse, first make a cheese emul-

sion, heating a pan and then adding water and small rounds of goat cheese

298 | a c uisine f or t omor r ow

(Chavignol, for example). Shake the pan gently. The result is a smooth, thick

sauce that under the microscope can be seen to be composed of droplets dis-

persed in water (for a sharper taste one can substitute vinegar for the water and

reduce it over high heat). This preparation we may call a “cheese béarnaise.”

To obtain the desired mousse, use the same procedure that turns cream (an

emulsion of milk fats in water) into whipped cream: cooling followed by whisk-

ing. In this case you put the pan in the freezer for about ten minutes and then

whisk the chilled sauce vigorously to make what might be called a Chavignol

Chantilly. The same method can successfully be used with Roquefort to yield a

Roquefort Chantilly, and so on.

Aioli Generalized
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90

Orders of Magnitude

Dispersed systems make it possible to get a lot from a little.

i n m a k i n g f l a n s o n e o f t e n s e e k s, for economic or dietary reasons,

to limit the proportion of egg or increase the proportion of water. How far can

one go in this direction? Much farther, certainly, than traditional cuisine has

yet gone. Let’s begin by analyzing two related cases: making mayonnaise from

a single egg yolk and making meringue from a single egg white.

Cookbooks often say that one egg yolk is enough to yield a large bowl of

mayonnaise. But in fact the physical chemistry of mayonnaise makes it pos-

sible, as we have already seen, to obtain liters of sauce from a single yolk: The

quantity of tensioactive molecules in an egg yolk (proteins and phospholipids,

equal to about 5 grams) is sufficient to cover a football field with a monomo-

lecular layer; and when these molecules cover oil droplets whose radius in on

the order of a micrometer (a millionth of a millimeter), as in the case of mayon-

naise, they suffice to stabilize several liters of sauce.

We have also seen that classic mayonnaises break because they do not have

enough water to sustain the dispersion of oil droplets. Verifying this claim

experimentally is a simple matter, but it means wasting a lot of oil. Instead try

making a large bowl of mayonnaise using only a single drop of egg yolk (the

source of the tensioactive material) dissolved in a teaspoon of water (or vinegar

if you want to taste the result).

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A Cubic Meter of Foam

A stiffly whipped egg white is essentially the same thing, only the oil in

mayonnaise (which is insoluble in water) has been replaced by air (also largely

water insoluble), and the tensioactive molecules that isolate the air are now

proteins, which make up 10% of the egg white. The result is no longer an

emulsion but a foam. And so our question remains essentially the same: How

much meringue can be obtained from a single egg white?

Here again, calculating orders of magnitude is simple. One begins by es-

timating the number of protein molecules in the egg white. Then one deter-

mines the total surface that can be occupied by these proteins and the number

of air bubbles that can be covered by these proteins. Multiplying this number

by the volume of a bubble, one obtains the maximum volume of meringue that

can be made from a single white: several liters, indeed several cubic meters,