Molecular Gastronomy: Exploring the Science of Flavor (8 page)

heat gradually becomes distributed throughout the soufflé, the evaporation of

the water as it comes into contact with the bottom of the ramekin produces

bubbles that push the whole of the soufflé upward, which in turn causes cold

layers of the mixture to rise to the level of the probe. These layers nonetheless

continue to heat up, and the cooking is done when the eggs have thoroughly

coagulated, at about 70°c.

In Search of New Heights

How does the water evaporate? Comparison of two soufflés that are identi-

cal except for the egg whites used in each suggests an answer: A soufflé with

very stiff egg whites rises higher than one whose whites have been whipped for

a shorter time because steam bubbles have a harder time penetrating the stable

foam of the vigorously beaten whites. Thus leavening is caused by at least two

things: the formation of steam bubbles and the trapping of this moisture in

the body of the soufflé, in areas where the temperature is sufficiently great to

avoid recondensation.

The Well-Leavened Souºé
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How much water is needed to increase the volume of a soufflé to its greatest

extent? Weighing a soufflé before and after cooking reveals that about 10% of

its mass has been lost, which is to say that for a soufflé that weighs 300 grams

(about 10 ounces), 30 grams (about 1 ounce) can evaporate. Keep in mind that

1 gram of liquid produces 1 liter, or slightly more than a quart, of vapor. None-

theless, not all the water in a soufflé remains trapped inside; otherwise the in-

ternal pressure would exceed a hundred atmospheres. Recent measurements

have shown that the pressure increases during cooking by only a few dozen

millimeters of mercury, which proves that only part of the evaporated water is

retained; the rest escapes in the form of bubbles that eventually burst at the

surface of the soufflé.

This suggests that the way to obtain a perfectly leavened soufflé is to heat

the bottom of the ramekin, to use very firm whipped egg whites, and to seal

the surface in order to prevent the release of the bubbles formed inside. How

would one go about doing this? One possibility would be to place the soufflé

under a broiler before putting it in the oven. This method has the additional

advantage that the soufflé then rises in a regular fashion and, when it is done,

has a smooth golden glaze on top that promises a rich flavor.

40 | secrets of the kitchen

7Quenelles and Their Cousins

They’re best cooked slowly after the dough has been chilled and allowed

to rest.

a s w i t h é c h a u d é s, often called gnocchi today, there are many recipes for

fish quenelles, but whether they call for salmon or trout or pike they are all

variations on a theme: To the finely ground flesh of the fish one adds fat (beef

kidneys, butter, or cream) and perhaps egg and panada (either bread soaked in

milk or a dough made by combining flour with boiling water). The ingredients

are kneaded for a long time—so long, in fact, that Isabella Beeton (author of

the famous cookbook published in England in 1860 as
Beeton’s Book of House-

hold Management
) wrote, “French quenelles are the best in the world, because

they swell up more.” And they swell up more, she explained, because they are

kneaded longer.

Why should kneading quenelles have anything to do with their succulence?

And why should quenelles hold their shape during cooking, even when they

do not contain any egg? Florence Lefèvre and Benoit Fauconneau at the Insti-

tut National de la Recherche Agronomique (inra) in Rennes have indirectly

answered the question by exploring the thermogelling properties of river (or

brown) trout.

The fleshy tissue of the trout is composed of cells, or muscle fibers, that

contain myofibrillary proteins. These proteins, which are responsible for

muscle contraction, form a gel when they are heated in a water solution. Like

the proteins in egg whites, the proteins in trout muscle tissue bind together,

| 41

creating a network that traps water. In a quenelle, this gel also traps fat and the

expanded starch granules contributed by the panada.

Understanding the chemistry of gelatinization allows us to make quenelles

and various other products from farm-raised salmon. These products, which

Norwegian companies hope to bring to market soon, would be culinary cous-

ins to Asian fish noodles and surimis (dumplings made from freshwater fish

such as carp, especially in China). In France, where farm-raised trout is more

common, the proteins of this fish are being studied with a view to creating new

products as well.

Which proteins form these gels? Like all cells, muscle fibers contain sarco-

plasmic proteins that regulate cellular function and maintenance. But they also

contain specific myofibrillary proteins, of which the main ones are actin and

myosin. In water solution, Lefèvre showed, only the myosin gels alone. The

actin by itself does not gel, although incorporating it in a myosin preparation

was found to increase the rigidity of the gel.

Under what conditions does gelatinization take place? In the case of quenel-

les, as in other dishes that depend for their effect on myofibrillary protein gels,

the practical problem is how to combine the greatest possible tenderness with

sufficient firmness. The parameters that determine the firmness of a gel are

the storage time of the solution, the rate of heating, and the maximum cooking

temperature, in addition to the protein concentration, acidity, and salt concen-

tration of the solution.

To study the effect of these factors, the biochemists in Rennes inserted the

pointed tip of a penetrometer into the trout with constant pressure and mea-

sured the degree of deformation. Having first established that this test gauges

firmness in the same way biting into the flesh of a fish does, the researchers

went on to analyze the gels formed by heating different protein solutions and

discovered that the maximum protein concentration was on the order of 10

grams per liter.

A Well-Deserved Rest

Firmness depends also on the length of time solutions are stored, for it

is during this time that protein interactions begin to form a gel. Its firmness

changes during cooking. A few minutes’ heating within a range of 70–80°c

(158–176°f) is enough to stabilize the incipient gel, but prolonged cooking re-

42 | secrets of the kitchen

sults in a loss of water and therefore of tenderness. A rate of heating of 0.25°c

per minute has been found to produce a sufficiently firm and elastic gel for

making quenelles.

Because proteins contain ionizable lateral groups, their behavior depends

especially on the acidity of the solution in which they are placed: In an acidic

environment, the acid groups of the proteins are unchanged, but the base

groups bond with a hydrogen ion, positively charging the protein molecules

and causing them to repel one another rather than to combine. Conversely,

in an insufficiently acidic environment, the base groups are neutralized while

the acid groups are ionized, likewise producing a repulsion. Thus the acidity

of the solution determines the bonds not only between proteins but also with

water molecules. The optimal acidity levels depend on the proteins involved

and on the animal species from which these proteins come. The inra chem-

ists showed that, in the case of river trout, the formation of gels is optimized

when the acidity of the protein solution is higher (a pH of about 5.6) than the

levels conducive to gelatinization in other fish.

This research makes it possible, finally, to perfect the classic preparation of

quenelles. First, the quenelle dough must be chilled and left to rest for a few

hours, so that a gel forms from the proteins released by the ground muscle

fibers. The quenelles themselves should then be heated gently, in a very low

oven. Finally, if the quenelles have been slightly acidified, the firmness this

imparts will yield a more tender result through the addition of extra water

(which in this case means a strongly flavored liquid such as shellfish fumet or

fish stock) during cooking.

Quenelles and Their Cousins
| 43

8Fondue

How to choose wines and cheeses so that the fondue never ops.

d o e s t h e t r u e c h e e s e f o n d u e come from Savoy in France, or the

Valais in Switzerland, or the canton of Fribourg? How many types of cheese

should be used? One? Two? Four? Connoisseurs passionately disagree. Wars

have been started for less. Physical chemistry may not permanently settle such

disputes, but it should at least enable lovers of the dish to reach agreement over

why, despite its simplicity, the fondue sometimes flops. Athony Blake, direc-

tor of food sciences and technologies for the Firmenich Group in Geneva, has

discovered a surefire way to prevent it from turning into a solid mass lying at

the bottom of the pot beneath a greasy liquid.

A fondue is no more than cheese heated with wine. The combination of

water (from the wine) and water-insoluble fat (from the cheese) means that

the successful fondue is necessarily an emulsion, a dispersion of microscopic

droplets of fat in water solution. The fondue therefore is a cousin to béarnaise

and hollandaise sauces, which are also obtained by the fusion and dispersion

of a fatty substance (in this case butter) in an aqueous phase or zone (from

vinegar and egg yolks).

In a béarnaise sauce, the fat droplets are coated by tensioactive molecules

found in the egg yolk, in such a way that the water-soluble (hydrophilic) part

of these molecules is exposed to the water and the water-insoluble (hydropho-

bic) part to the fat. The surface-active molecules that cover the fatty droplets

in a fondue are known as casein proteins, which are already present in the

44 |

milk, itself an emulsion, and which combine to form aggregates called mi-

celles. These aggregates are made up of several types of casein, bound together

by calcium (especially phosphate) salts. One of the caseins, the kappa-casein,

typically lies outside the micelles and ensures their mutual repulsion (because

of the negative electrical charge they bear). This repulsion is important for the

stability of the milk, for it prevents the coalescence of the fatty droplets covered

by the micelles.

In cheesemaking, the rennet that is added to the milk contains an enzyme

that detaches a part of the kappa-casein, triggering the aggregation of micelles

into a gel in which the fatty matter is trapped. Cheese therefore seems an un-

likely candidate for reviving an emulsion in the fondue, having been formed

from a milky emulsion that has deliberately been ruined. It nonetheless lends

itself to this purpose because it has been aged and mixed with wine.

Aging and Viscosity

Connoisseurs of fondue know that the success of the dish has to do particu-

larly with proper cheese selection. Questions of flavor come into play as well,

but well-ripened cheeses are best suited to the preparation of fondues because,

in the course of aging, enzymes called peptidases have broken up the casein

and the other proteins into small fragments that are more readily dispersed

in the water solution. These casein fragments then emulsify the fatty droplets

and increase the viscosity of the aqueous phase (which is why a Camembert

fondue, for example, will always turn out well).

This increase in viscosity is analogous to the heretical practice of thicken-

ing a fondue by adding flour or any other ingredient containing starch, such

as potatoes. Swelling up in the warm aqueous solution, the starch granules

increase its viscosity and limit the motion of the fatty droplets, which thus are

kept separate from one another. In this way the emulsion—which is to say, the

fondue—is stabilized.

To Doctor or Not to Doctor

Connoisseurs challenge this practice on the ground that it changes the taste

of the dish, insisting instead on the skillful combination of cheeses and wines.

They select very dry wines—indeed, wines that are excessively acidic and, if

Fondue
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possible, very fruity. Why are these properties useful? Athony Blake has shown

that such wines have high concentrations of tartaric, malic, and citric acids.

Malate, tartrate, and especially citrate ions are very good at chelating (or se-

questering) calcium ions. The acidic and fruity wines experts prefer help sepa-

rate the casein micelles and release their constituent proteins, which stabilize

the emulsion by coating the fatty droplets.

Chemists have devised ways to tweak the classic recipe for fondue, for ex-

ample by adding bicarbonate of soda, which neutralizes the acids and encour-

ages the formation of calcium-chelating ions. Another option, if one suspects

that the wine contains too little tartaric, malic, or citric acid, is to add some; the