Read Molecular Gastronomy: Exploring the Science of Flavor Online
Authors: Hervé This
Tags: #Cooking, #General, #Methods, #Essays & Narratives, #Special Appliances, #Science, #Chemistry, #Physics, #Technology & Engineering, #Food Science, #Columbia University Press, #ISBN-13: 9780231133128
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
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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