Molecular Gastronomy: Exploring the Science of Flavor (12 page)

purplish color to appear because the pigments in the red fruits have combined

with the metallic atoms; and because the electrons responsible for this bond

are differentially distributed in the molecules of the pigments, these pigments

absorb light to different degrees. Thus silver salts cause raspberries to whiten a

bit, whereas copper ions give them a fine red-orange color. Tin ions trigger the

purple tinge that has given rise to the prejudice against tin-plated pans.

Modern cleaning methods are superior to those in times past, however, and

so the dictum must be amended: Red fruits should never be placed or cooked

in unclean tin-plated copper pans.

Preserves and Preserving Pans
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16

Saving a Crème Anglaise

A pinch of our prevents the formation of protein aggregates, which none-

theless can be broken up in a mixer.

h o w c a n o n e s a v e a c r è m e a n g l a i s e that has curdled? The ques-

tion is of culinary importance because crème anglaise figures in one form or

another in many desserts. One of the differences between crème anglaise and

crème patissière, for example, is that although both are composed of milk, egg

yolks, sugar, and an aromatic ingredient such as vanilla, crème patissière ad-

ditionally contains a certain amount of flour, which protects against curdling.

Crème anglaise, lacking this protective agent, is more liable to turn.

The Second International Workshop of Molecular Gastronomy, held in

April 1995 at the Ettore Majorana Center in Sicily, brought chefs and physical

chemists together to examine such questions. Two renowned chefs, Christian

Conticini and Raymond Blanc, raised a series of issues relating to sauces and

dishes derived from them: crème anglaise, crème patissière, mayonnaise, stiff-

ened egg whites, soufflés, chocolate cream fillings, jellies, preserves, and so on.

The physicists and chemists, led by Nicholas Kurti, Pierre-Gilles de Gennes of

the École Supérieure de Physique et de Chimie Industrielles in Paris, and me,

sought to identify the mechanisms for culinary effects that were plain to see

but not yet understood scientifically, regarding sauces as solutions, emulsions,

foams, gels, suspensions, and so on.

At the conference the problem of crème anglaise was examined experimen-

tally. Like many other delicate dishes, crème anglaise has inspired many dic-

tums and ad hoc remedies that are worth scrutinizing. It has long been said

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that a pinch of flour added to crème anglaise will keep it from curdling. Why

should this be so? Is it true that a crème anglaise that has turned can be saved

by vigorously shaking it in a blender?

The Pinch of Flour and the Blender

Crème anglaise was examined at different stages of preparation. First, the

custard was gently heated (at a lower temperature of 65°c [149°f]); gradually,

as in the case of every successful crème anglaise, the mixture of milk, sugar,

and egg yolks thickens. Under the microscope, small-scale structures (a few

micrometers long) can be seen.

Then this same custard was put in a microwave oven for a few seconds so

that a curd—a sign of overcooking—would appear. The observed microscopic

structures were about twice as large and dense as those that had been observed

in the successful custard, but their general aspect was not substantially differ-

ent. When the custard was overheated, its appearance under the microscope

changed completely: Clear liquid areas separated very dense areas composed of

structures similar to those that had been observed at the onset of curdling.

Finally, this botched crème anglaise was mixed for a few dozen seconds. To

the naked eye it had become frothy. The curdles had disappeared, and the tex-

ture of a perfect custard seemed to have been restored; under the microscope,

however, a state of aggregation intermediate between that of a perfect custard

and that of the initial stage of curdling could be discerned.

Inevitable Coagulation

It seems clear that the setting of a crème anglaise depends on the coagula-

tion of the egg yolk, which occurs whether the result is successful or not. The

structures observed under the microscope probably are aggregates of proteins

that have been partially broken down by the heat, then reassembled by means

of weak chemical bonds.

When the crème anglaise has been excessively heated, coagulation is rapid

and produces macroscopic aggregates, evidence of curdling, which can be

eliminated by mixing. Has the possibility of curdling thereby been completely

removed? Can a perfect crème anglaise be reconstituted by putting a botched

one in a blender?

Saving a Crème Anglaise
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Microscopic analysis shows that although a blender does a good job of dis-

sociating the macroscopic aggregates, more agitation is needed if the result is

to contain only microscopic protein aggregates, similar to the ones found in a

successful sauce. Those whose palate is sufficiently refined to detect the omelet

taste characteristic of a botched crème anglaise can prevent the sauce from

curdling in the first place by adding a pinch of flour before cooking. Curdling

will not take place, even if the crème anglaise is boiled.

The reasons for this protection are still a subject of debate, but it is known

that placing starch granules in a hot liquid triggers the release of amylose mol-

ecules and that the water penetrates the granules and causes them to swell.

These swollen granules, together with the long, dissolved amylose molecules,

limit the movement of proteins, blocking the formation of macroscopic protein

aggregates.

70 | secrets of the kitchen

17

Grains of Salt

Culinary myths and legends of the white gold.

m y t h s a b o u t s a l t d i e h a r d. For example, some cooks recommend

adding salt only to water that is already boiling because salty water, they say,

takes longer to boil than pure water. This rule is widely believed, but is it justi-

fied?

Or consider the question of boiling meat to make stocks. Many cookbooks

say that meat should be salted first in order to better extract its juices. Is the

promised efficiency real or illusory? On the other hand, salad is not to be salted

too far in advance because seasoning it in this way will wilt the leaves. What is

one to make of this dictum, which comes from Japan?

With regard to vegetables, the French chemist Michel-Eugène Chevreul re-

corded the following observations in
Recherches des matières fixes tenues en dis-

solution dans l’eau pure ou salée, qui a servi à la cuisson des légumes
(1835): “Water

used for the decoction of vegetables had a reddish-brown color; it retained a

sensible quantity of the odiferous principles. Salted water used for the cook-

ing of the same vegetables had a more pronounced fragrance than pure water;

its flavor, allowance being made for the flavor peculiar to salt, was also more

pronounced, and yet, remarkably, it contained a lesser proportion of extractive

matter.” Is this account to be credited?

We should be wary of assertions that are not supported by sound experi-

ments. With respect to the first claim, it is true that adding salt to water cools

it down (because the water loses energy in dissolving the salt) and raises its

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boiling point and that the mass of fluid to be heated is greater. But whether

salt is added before or after the water has been brought to a boil, all three

phenomena are equally in play. If we heat water with and without salt (the

same quantity of water, in the same pan, heated in the same way), we find

that, within the limits of experimental error, the time needed to bring it to a

boil is the same.

With regard to stock, it is commonly maintained that the major effect of

salting the meat in advance is to promote osmosis. Heating causes the vari-

ous molecules to move apart so that their final concentrations are everywhere

the same, but because the larger molecules do not pass through the cellular

membranes, it must be water that enters or leaves the cells, depending on

the case. If one takes into account only this effect, one would predict as a

theoretical matter that the meat must lose more juice when it is cooked in the

presence of salt. Let us then conduct a simple but careful test. Put two identi-

cal pieces of meat in two identical pans, one containing pure water and the

other water that has been salted to the saturation point. Now cook them for

the customary five hours, weighing the two pieces every ten minutes. After

the prescribed time has elapsed, the mass of the two pieces is the same, give

or take a gram.

Would eggs react differently? It is sometimes said that the water used for

cooking hard-boiled eggs must be salted because otherwise the water would

infiltrate the eggs by osmosis, causing them to expand and to crack. Let’s cook

a dozen eggs in a pan full of pure water and a dozen eggs in a pan identical

to the first, filled with the same quantity of water, only this time highly salted.

Again, let’s weigh the eggs at various stages of the cooking process to deter-

mine whether the suspected osmosis actually causes their weight to increase.

Then we will count the number of cracked eggs in each batch.

Going to all this trouble is worthwhile because it reminds us of something

that chefs knew in the nineteenth century but have forgotten since. Although

salting the water does not prevent the shells from cracking (the best way to

ensure that they don’t is to pierce the eggs with a needle, which by permitting

the air trapped inside the egg to escape more easily preserves the integrity of

the shell), it seasons the white of the egg, imparting flavor to an otherwise

tasteless material.

72 | secrets of the kitchen

Wilted Salad

Let us now turn to the effect of salt on vegetables. How do salad greens react

when they are sprinkled with table salt? It turns out that there is no reaction,

even after several hours, as long as the lettuce is dry. This is because its leaves

are covered with a waxy cuticle that prevents osmosis.

What about vegetables cooked in water? To determine how much matter is

lost during cooking, let’s experiment with onions and carrots, covering the pan

and weighing them at intervals. Onions, it turns out, lose more of their mass

when they are cooked for a short time in salted water. In this case the effects of

osmosis are plain. With carrots, however, there is no great difference. In both

cases the vegetables decompose more when they are cooked in salted water, but

if the cooking goes on too long, they both wind up in the same degraded state

whether or not salt has been added to the water.

Why do explanations that assume osmosis do a poor job of predicting the

actual behavior of vegetables and meats cooked in water? A glance through the

microscope gives the answer: Animal and vegetable cells are not covered with

semipermeable membranes through which osmotic transfer can take place.

Muscle cells are sheathed by collagen, and vegetable cells are protected by a

rigid wall. Some degree of osmosis may occur at the beginning of cooking, but

over time the structure of the cells is degraded, with the result that they open

up and absorb fluid like a sponge. Salt doesn’t change anything.

There are many other such dictums. Putting cooked and peeled potato in a

sauce that is overly salty, it is said, will remove the saltiness. Some chefs claim

to be able to see tiny shimmering particles in sauces that have been oversalted.

In the fourteenth century, Guillaume Tirel (known as Taillevent) noted that

soups and stews tend to boil over if salt and fat are not added to them. In the

case of grilled meats it is often said that salt should not be added at the begin-

ning of cooking but reserved until the end so that it will be soaked up by the

meat. To remove extra salt from a dish, Ginette Mathiot, author of the bestsell-

ing
La cuisine pour tous
(1955), advised immersing a cube of sugar in it for two

seconds. What do you make of these recommendations?

Grains of Salt
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18

Of Champagne and Teaspoons

A teaspoon in the neck of a bottle of champagne does not prevent the bub-

bles from escaping.

a t e a s p o o n p l a c e d i n t h e n e c k of a bottle of opened champagne, it

is said, will help preserve its fizz for a certain time. Some even go so far as to

claim that the effect occurs only with silver spoons. What reason is there to be-

lieve such dictums, which seem to be the product of nothing more than unsci-

entific experimentation? By virtue of what strange physicochemical principle

could a teaspoon trap the bubbles of this noble beverage of celebration? As it

happens, there is no need for us to inquire into this matter ourselves because

the Comité Interprofessionnel du Vin de Champagne has already carried out a

rigorous series of experiments on the “teaspoon effect.” Their findings, which