Molecular Gastronomy: Exploring the Science of Flavor (47 page)

pressure. But because it is formed of several types of molecule, its fusion point

extends over a range of temperatures from –7°c (19°f) for some of the triglyc-

erides to 34°c (93°f). Even so, 75% of the constituents of cocoa butter melt

between 20°c and 34°c (68°f and 93°f) and almost 50% between 30°c and 34°c

(86°f and 93°f). In other words, although chocolate is not a pure body, it is not

very far from being one.

This characteristic, which is an advantage in eating chocolate bars, is trouble-

some for the cook, who generally uses it at temperatures in the neighborhood

of only 20°c (68°f), hence the difficulties involved in using it in puff pastry,

in particular. Comparing cocoa butter with ordinary butter, a more heteroge-

neous substance, suggests a way to overcome them: The less pure the choco-

late, the more malleable it will be. This isn’t a new idea; cooks have long been

accustomed to melting chocolate with butter in order to obtain softer chocolate

preparations. Nonetheless, one can take the idea farther by heating a neutral

oil and adding chocolate to it. The chocolate mixes perfectly with the oil, which

modifies the fusion properties of the chocolate in the desired manner.

Not only does this method enable us to make chocolate puff pastry (another

solution, by the way, would have been to add cocoa powder to flour or to ordi-

nary butter), the underlying principle makes it possible to reconfigure recipes

for all kinds of desserts.

Make All Desserts with Chocolate

From puff pastry it is but a short step to make both shortcrust pastry (in-

cluding the basic pie dough used to line meat or fish pies) and sugar crust with

chocolate; one has only to replace butter with chocolate whose lipid composi-

tion has been changed. Similarly, one could make chocolate savarin dough,

chocolate brioche dough, chocolate cream puff dough, almond or chocolate

cookie dough, and so on. One might even be tempted to use chocolate in an

almond custard: Add almond powder and an alcohol to melted chocolate, and

Everything Chocolate
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then fold in the crème pâtissière (made by cooking egg yolks, sugar, milk,

and flour).

Where the fatty matter used is cream rather than butter, it is the cream

that must be replaced by a chocolate preparation. In this case it is not enough

to manipulate the melting point of the chocolate, for cream is above all an

emulsion, a dispersion of fatty droplets in water (from the milk). The droplets

remain separated from one another for a long time, though not indefinitely,

because they are surrounded by tensioactive molecules, one part of which is

hydrophilic (immersed in the water) and another part hydrophobic (immersed

in the oil). To replace the cream you will have to make a chocolate emulsion,

which is not difficult. In a pan, heat water or a watery solution (coffee, tea,

Cognac) together with squares of chocolate. The resulting “chocolate béar-

naise” is chemically the equivalent of cream.

Finally, to make a chocolate bavarois (Bavarian cream), a new procedure is

necessary. We begin by following the classic recipe to make a crème anglaise:

Whisk powdered sugar and egg yolks together, add milk to the mixture, and

cook it, then dissolve gelatin in the custard and fold in whipped cream. The

problem is how to incorporate the chocolate. It cannot be substituted for the

egg yolks, for it is their coagulation that gives the crème anglaise its texture, as

particles of the cooked egg are suspended in the water of the milk. Nor can it

be substituted for the gelatin.

How about replacing the cream with chocolate? No; the recipe calls for

whipped cream. Forget the recipe! Whip up an emulsion of chocolate instead,

just as we did in the last chapter to make our Chantilly chocolate, and add this

mousse to the final preparation.

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98

Playing with Texture

Gelatinizing emulsions produces a new kind of chocolate cake.

e m u l s i on s a r e a n i n e x h a u s t i b l e s o u r c e of culinary discoveries.

Here we will use them only as a point of departure for investigating more com-

plex physicochemical systems that anyone can use in cooking.

In the preceding chapters we have considered several types of emulsion,

foremost among them mayonnaise, the prototype described by all textbooks

dealing with the physics of soft matter. Mayonnaise is a dispersion in water of

oil droplets stabilized by the proteins of the egg yolk. A great many variations

on this theme are possible. We have already looked at two of them: one made

without a yolk, the other without any egg at all.

A yolkless mayonnaise is made in the same way as a classic mayonnaise,

but in place of the yolk one uses the white of the egg. Albumen is made up

of 90% water and 10% proteins, which have the same type of tensioactive

properties as the proteins of the yolk. In a bowl one adds oil to an egg white,

drop by drop, while whisking. At first the albumen foams, but gradually the

air in the bubbles is replaced by the oil, which comes to be divided into

smaller and smaller droplets by the shearing action of the whisk. The oil

droplets, like the bubbles, are stabilized by the proteins of the egg white, for

the proteins are unfolded in the course of whisking, so that their hydropho-

bic parts come into contact with the oil while the hydrophilic parts remain

immersed in the water.

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An eggless mayonnaise may be obtained by dissolving a half-sheet of gela-

tin in a small amount of heated water (or, for example, stock made from shell-

fish) and then whisking oil into the liquid just as one does in the case of a

mayonnaise. At first a white emulsion appears as the proteins contributed by

the gelatin attach themselves to the oil droplets at the interface of the water and

oil. Once this emulsion has settled and cooled, it is transformed into a gel as

the gelatin molecules become linked together at their extremities, forming a

network within which the emulsified liquid is trapped.

Gelatinized Emulsion

The process of gelatinization can be viewed indirectly under the micro-

scope. The oil droplets partially coalesce because the gelatin molecules coating

them migrate away from the water–oil interface, forming a network (or gel)

that traps the enlarged droplets. Once the gel has formed, by the way, whisking

it again causes it to break down (in a classic mayonnaise, by contrast, the gel

is stabilized further by whisking). Beating the gel dissociates the bonds of the

network, with the result that the oil droplets are released.

The principle of a gelatin-based mayonnaise, then, is that an emulsion is

created and then trapped in a physical gel, which is to say a gel that breaks

up on being heated and reforms on being cooled. Can we devise additional

variations on this theme by changing certain ingredients? Let’s go back to the

mayonnaise made with egg whites and look for a way to chemically gelatinize

it—in other words, to cook it. What we want to end up with is a chemical gel

that, as in the case of gelatin itself, is permanent rather than physical.

Cooking Mayonnaise

Let’s begin by cooking the egg white mayonnaise in a microwave oven for

about a minute so that the proteins covering the oil droplets are fused. What

we get is a coagulated mass in which the oil is trapped, which is to say a physi-

cal system similar to a gelatinized mayonnaise. But is the oil securely retained

by this body? If you squeeze the gel you will see that the oil comes out.

By manipulating the texture of the mayonnaise we seem only to have creat-

ed a sponge for soaking up oil. Let’s try replacing the oil with chocolate (which

326 | a c uisine f or t omor r ow

is composed mostly of cocoa butter) and melting it in a pan with a bit of liquid

that contains water (whether from rum, coffee, orange juice, or something

else). Then, when the temperature of the resulting chocolate emulsion is still

lower than the temperature at which albumen coagulates (62°c [144°f]), whisk

the chocolate emulsion into an egg white. Finally, put this mixture in the mi-

crowave. What will happen? The proteins of the egg white will gelatinize and

imprison the chocolate emulsion.

If you try this experiment yourself you will end up with a delicious choco-

late cake whose flavor is much more powerful than that of an ordinary choco-

late cake, probably because the chocolate is in a dispersed state, producing a

novel texture (which you can vary as you like by modifying the proportions of

water and chocolate). I suggest calling this dessert a chocolate dispersion. It

remains to study how gelatinization disturbs the emulsion in the three systems

we have considered.

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99

Christmas Recipes

A few ideas for modernizing holiday meals.

t h e ho l i d a y s a r e h e r e — time to set to work in the kitchen. Should we

be satisfied with cooking a turkey with medieval methods now that we are liv-

ing in the twenty-first century? No, let’s invent new dishes. But how? The cook

who looks to chemistry and physics for inspiration will not find it difficult.

Let’s begin by considering a new mode of cooking based on a remark by

François Pérégo, a restorer of paintings in Bécherel and a keen student of

chemistry who uses egg in treating canvases. He pointed out the effect of ethyl

alcohol on egg whites, which you can see by means of a simple experiment:

Put an egg white in a bowl and then add a shot of grain alcohol (190 proof).

You will discover that the white quickly coagulates.

How can we explain this phenomenon? Albumen is made up of about 90%

water and about 10% proteins. These molecules consist of amino acids (twenty

types of which are found in foods) that are distinguished by their lateral chains,

which may be either hydrophobic or hydrophilic. In water the hydrophilic parts

fold up over the hydrophobic parts, minimizing the contact of these latter parts

with the water.

The addition of a very strong alcohol alters the environment of the pro-

teins, causing them to unfold. A reaction between two thiol (–sh) groups of

neighboring proteins creates a disulfide bridge—a bond between two sulfur

atoms—that binds the proteins. Thus a gel is formed, in effect cooking the egg

white. Naturally this chemical process cannot be used for culinary purposes

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without modification: The egg white is tasteless, and alcohol in a nearly pure

state holds little appeal from the point of view of flavor. But what if we were

to replace the alcohol with a yellow plum brandy, for example, to make a
blanc

d’œuf à la mirabelle?
That would be an unusual cocktail to put your guests in

the holiday spirit!

Reasoned Braisings

In thinking about a novel main course for our meal it will help to keep

in mind some basic scientific facts about the transformations undergone by

heated meat. At 40°c (104°f) proteins unfold, becoming denatured, and the

meat loses its transparency; at 50°c (122°f) collagen fibers, the chief structural

component of muscle cells, contract; at 55°c (131°f) myosin, one of the principal

proteins of muscle cells, coagulates and the collagen begins to dissolve; at 66°c

(151°f) the sarcoplasmic proteins that make up collagen coagulate; and at 79°c

(174°f) actin, another important muscle protein, coagulates.

What use can we make of this information? Instead of cooking your turkey

in the usual way, remove the white meat, slice it, and cook some pieces at

50–55°c (122–131°f), others at 55–66°c (131–151°f), and so on (either in the oven,

if the temperature control is very precise, or in a pan with stock, using a ther-

mometer). Your guests will be able to enjoy different textures in a single meat

because different compounds in the meat will have reacted with one another.

Foamy Foie Gras and Cheese

Now for the cheese course. Earlier we saw how to make Chantilly chocolate,

a mousse made of (rather than with) chocolate. Why not repeat this experiment

with foie gras? Pour a glass of duck stock into a pan, add some foie gras, and

stir over low heat. The melting foie gras forms fatty droplets that are dispersed

in the water. Whisk this mixture in a bowl over ice cubes and you will achieve

the consistency of whipped cream.

The same thing can be done with cheese. Pour a glass of water or vinegar

in a pan, add a sheet of gelatin and a good chunk of cheese (Roquefort, for

example), and stir over low heat. The melting cheese forms fatty droplets that

are dispersed in the water and covered by the tensioactive molecules of the

gelatin. The result is a “cheese béarnaise” that is a cousin not only of many

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other culinary emulsions, such as mayonnaise, béarnaise sauce, and cheese