Molecular Gastronomy: Exploring the Science of Flavor (41 page)

costly business. Imagine going to the trouble of cooking a stock for several

hours and then having to re-enrich it because cooking has impoverished it.

Chemists, for whom filtration is a daily activity, solved this problem long

ago with the aid of various devices adapted to specialized purposes. Indeed, the

catalogue of one leading supplier of laboratory equipment today devotes more

than forty pages to such devices. One of the most commonly used models has a

funnel equipped with a fritted glass plate (which, unlike paper filters, does not

tear) containing pores of uniform size. The matter to be filtered is deposited

in the funnel, and the funnel is then placed on top of a conical vial in which a

vacuum has been created by means of a waterjet pump, an inexpensive device

that attaches directly to a faucet.

Antoine Westermann, the chef at Buerehiesel in Strasbourg, and I tested

this apparatus with a tomato consommé that he wanted to be perfectly clear.

The original recipe called for cooking the tomatoes in water to which egg

whites had been added. After a half hour of slow cooking, straining the mixture

through a cloth-lined chinois yielded a golden liquid. The laboratory device,

on the other hand, yielded both a clearer liquid and a more pronounced taste.

What prevents the makers of electric household appliances from producing

this piece of equipment on a large scale? They would have only to increase the

filtration capacity of the laboratory device and replace the glass with metal that

will stand up to rugged use in commercial and home kitchens.

Other culinary uses for waterjet pumps can readily be imagined as well.

Nicholas Kurti thought to use one to produce a new kind of meringue. Clas-

sically one makes meringues by adding sugar to egg whites that have been

beaten until they are stiff and then cooking this mixture over very low heat. The

coagulation of the proteins in the egg whites conserves the alveolar structure

of the “floating islands,” while the water slowly evaporates, leaving a vitreous

sugar residue. Kurti had the idea of substituting vacuum storage for heating.

In this case the water evaporates while the dilation of the air initially present

in the bubbles causes the meringues to greatly expand. The final result is light

and airy—like “wind crystals.”

From Meringue to Soufé

Although it has the virtue of showing how vacuum techniques can be

used in cooking, this procedure is not altogether satisfactory, for the new

280 | a c uisine f or t omor r ow

meringues are
too
light and airy—there’s nothing to bite into. On the other

hand, we can increase expansion and have something left to eat afterward if

we choose a preparation in which the walls between the bubbles are thicker

than in meringues. Soufflés and cream puff pastries come to mind as attrac-

tive candidates.

If one combines the ingredients needed to make a soufflé—flour, butter,

milk, and eggs—in a vacuum bell jar the mixture swells up when the air is

pumped out, for the air bubbles in the preparation expand, but the soufflé col-

lapses when it is put back in atmospheric pressure. To prevent this from hap-

pening one needs to cook the soufflé in its expanded state—for example, with

the aid of an electric heating element wrapped around the ramekin—in the

vacuum bell jar. Heating it in this way causes the proteins to coagulate and the

bubbles to swell up with water vapor, so that the soufflé preserves its structure

when it is put back in atmospheric pressure.

No doubt many other uses for vacuums will be found once cooks decide to

exchange medieval for modern equipment.

Cooking in a Vacuum
| 281

84

Aromas or Reactions?

Two ways of imparting avor to food.

“ t h i n g s o u g h t t o t a s t e l ik e w h a t t h e y a r e,” the gastronome

Curnonsky used to say. His aphorism has been adopted as a slogan by those

who seek to promote authenticity in cooking, but does it really make sense?

Isn’t the role of the cook to transform foods with the purpose of recreating

traditional dishes and inventing new ones?

If the true aim of cooking is to produce specific flavors, the question aris-

es how to incorporate them in various dishes. There are two ways: by add-

ing flavors or by organizing chemical reactions in such a way that flavors are

formed in the foods themselves. One technique that has been widely used

by the food processing industry involves both natural extracts and synthetic

molecular solutions. The use of these so-called aromatic preparations in cook-

ing is straightforward (one simply adds a few drops to the food), but devising

them takes the same kind of technical artistry possessed by the “noses” of the

perfume industry, laboratory chemists who concoct novel solutions of various

odorant molecules in order to approximate or reconstitute familiar scents such

as strawberry, ginger, and rosemary.

Cooks are understandably reluctant to allow themselves to be supplanted

by such technicians, all the more because the use of natural ingredients (real

thyme and real rosemary in a ratatouille, for example) often gives a richer,

and certainly more varied aromatic result than artificial thyme or rosemary

282 |

flavoring (which usually do not contain as many aromatic molecules as natural

ingredients).

Must we therefore dismiss such aromatic engineering altogether? This

would mean foregoing the opportunity to enlarge the palette of flavors. Why

not reinforce the green note of olive oil with hexanal, or add 1-octen-3-ol to a

meat dish in order to give it an aroma of mushroom or mossy undergrowth

(although here one needs to be careful about proportions because in excessive

concentrations the same molecule smells a bit moldy)? Why not use beta-ion-

one to give desserts the surprising violet aroma that flowers have such a hard

time releasing?

Cooks would be also able to create taste, rather than flavor, by using mono-

sodium glutamate and other molecules that impart the taste called umami,

which is naturally contributed by onions and tomatoes. They would be able

to use licorice or glycyrrhizic acid, which communicate specific tastes that are

neither salt, sugar, sour, nor bitter—nor umami.

Advanced Uses of Fire

Need we worry that in this case culinary progress would be limited to chem-

ical aromatization, which is only a modern version of adding fines herbes and

spices to foods? Certainly not: Cooks well know that cooking transforms the

taste of their creations. Fire is their inseparable ally, and chemistry can help

them make the most of it.

For example, one can easily change the flavor of caramel by varying the

type of sugar. Caramels can be made from glucose, fructose, or, more gener-

ally, from sugars other than sucrose (ordinary cane sugar). An experiment

that anyone can perform will show that these caramels may already be present

in foods. It is based on an apparently paradoxical observation made by cooks

who, in the course of making a béarnaise sauce, for example, reduce a combi-

nation of chopped shallots and white wine until the liquid is completely evapo-

rated: Certain white wines leave no residue in the pan. Why? Because they lack

glucose, glycerol, and many other things. The practical lesson is this: If your

wine is insufficiently rich in such aromatic molecules, add some glucose to it

before reducing
à sec
and you will obtain a glucose caramel that improves the

flavor of the sauce.

Aromas or Reactions?
| 283

The Paradox of Reductions

There is something puzzling about even a reduction that has been fortified

in this way, however. Why should one want to evaporate most of the aromatic

molecules that are present in wines? The same question arises in the case of

stocks, which are made by concentrating beef broths through heating. If this

concentration has the effect of eliminating the aromatic molecules, why are

stocks nonetheless fragrant and flavorful?

Anthony Blake and François Benzi at the Firmenich Group in Geneva used

chromatography to compare a stock that had been reduced by three-quarters

and then restored to its initial volume by the addition of water with the same

stock that had not been topped off. Although the concentration of certain aro-

matic compounds was reduced by boiling, other compounds were created by

heating-induced reactions between the components of the stock. It remains to

identify these reactions in order to improve the making of stocks, if possible.

On Chemistry in Cooking

The possibilities of chemistry are unlimited. Our kitchen shelves hold a

great many nearly pure ingredients: sodium chloride, sucrose, triglycerides

(in oil), ethanol, acetic acid, and so on. And the shelves of our libraries con-

tain a great many chemical treatises that perfectly describe the reactions of

these molecules. The challenge facing cooks and chemists today is to apply this

knowledge in order to create new flavors.

Take Maillard reactions between amino acids and certain sugars, which pro-

duce the tasty brown compounds in the crust of roast beef and bread as well

as the aromas of coffee and chocolate. Chemists know that these reactions

differ according to the acidity of the reactional environment. Why not soak

chicken breasts in vinegar or bicarbonate of soda before putting them under

the broiler? To obtain the right degree of acidity once the reaction has occurred,

the vinegar could be neutralized with bicarbonate of soda or vice versa.

284 | a c uisine f or t omor r ow

85

Butter: A False Solid

How to make it spreadable.

b u t t er i s a s t r a ng e s o l i d : When one takes it out of the refrigerator

it is sometimes necessary to wait as long as fifteen minutes before it can be

spread easily. Would it be possible to make a butter that is spreadable immedi-

ately after being removed from the refrigerator?

The question has been around since 1988, when legislation in France

granted a butter appellation to products that, like butter, consist of droplets of

water in milk fats, on the condition that such products have been separated

by physical methods. Thus one could imagine selling butters having various

properties, prepared by mixing together various ingredients that were first iso-

lated from butter.

How would one go about separating and recombining these ingredients? In

1992 the research department of the dairy manufacturer Arilait hired several

laboratories to analyze milk fats and to identify the physical principles govern-

ing spreadable butters. The analysis was complicated by the fact that the mol-

ecules that make up milk fats are various and polymorphous; that is, each type

of molecule crystallizes in several ways, depending on the sort of processing

it has undergone, and the crystals assume their equilibrium form only after a

long resting period.

In milk the fatty matter assumes the form of droplets dispersed in water.

Each droplet is a few micrometers in diameter and coated with casein mi-

celles, each micelle being a collection of several proteins cemented together by

| 285

calcium phosphate. Aromatic molecules are dissolved in the fatty matter of the

droplets, and other molecules (vitamins, sugars such as lactose, mineral salts,

proteins) are dissolved in the water of the milk.

A team sponsored by Arilait first studied this fatty matter, whose compo-

sition changes even with the seasons. But there is unity as well as diversity:

The fatty matter in milk is made up of triglyceride molecules, composed of

a glycerol molecule to which three fatty acid molecules are bound (although,

of course, the glycerol and fatty acid molecules lose their identities, as when

oxygen and hydrogen molecules combine to form water). On the other hand,

milk contains more than 500 such fatty acids, and because each acid can bind

with any carbon atom in glycerol, the number of possible triglycerides exceeds

several thousand.

Strange Fusion of Butter

One of the chief consequences of this diversity is the strange behavior of

butter at the point of fusion. Unlike a pure body such as water, which melts at a

fixed temperature (0°c [32°f]), the fusion of butter begins at –50°c (–58°f) and

ends at about 40°c (104°f). The various triglycerides in milk melt in three prin-

cipal stages involving homogeneous chemical families: From –50°c (–58°f) to

10°c (50°f) one observes the fusion of molecules whose fatty acids are short

and composed of double chemical bonds among carbon atoms; between 10°C

(50°f) and 20°c (68°f) one sees the fusion of molecules containing a single

double bond or a short chain; finally, between 20°c (68°f) and 40°c (104°f) one