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Step 1: Forget
most of what you know about classic French cooking
 If you have ever taken a course in classic
French cooking, forget almost everything they told you. The French,
with great intestinal fortitude, thickened sauces with butter,
flour, egg yolks, and cream, to name a few of the culprits. They
whisk together butter and flour (a roux) and then add in milk
(a béchamel) or stock (a velouté), which thickens
almost immediately. They use a paste, or little balls, of equal
parts of flour and butter (beurre manié). These were added
to sauces or stews as a thickener near the end of cooking. They
also used egg yolks whisked into a sauce and reduced cream (cream
that has been boiled down to thicken it).
Butter can also be used as a
thickener. When it is whisked into a hot liquid, the milk solids
and proteins in butter form an emulsion that suspends the particles
of fat in the liquid, creating a thicker, shinier sauce. The
problem with this last method, however, is that you need lots
of butter to make this work (1/2 cup of butter is needed per
1 cup of liquid--1/2 cup of butter is an entire stick!). Nobody
in their right mind is going to thicken with butter these days.
Other thickeners include blood, foie gras (goose liver), yogurt,
fresh cheese, and bread. Prior to the 16th century, coarse bread
and ground almonds were the thickeners of choice.
So much for haute cuisine. The
quickest and easiest thickener for a home cook is cornstarch.
Whisk it with equal parts of water and then add it to a stock
or a gravy and you have an instant sauce. This is how most people
thicken gravy for Thanksgiving. But there are three good alternatives.
Since most thickeners are starch, the two most obvious thickeners
are potatoes and rice. Potatoes are particularly well suited
to soups and stews (cook extra potatoes with the dish and then
purée some of the liquid with the excess potatoes). I
often keep extra cooked rice in the refrigerator as a thickener
as well. I use it with stock and puréed vegetables for
a quick and light sauce. I also use stale white bread, which
is the traditional thickener for a rouille, a sauce made with
roasted red peppers, lots of garlic, and hot peppers.
The Science
of Cooking
Why do flour and cornstarch
thicken sauces?
You've probably noticed that
when stirred into water at room temperature, neither flour nor
cornstarch thicken. They just turn into a loose paste. What is
missing is the application of heat, which encourages the bonding
of starch and water molecules. (Both flour and cornstarch are
mostly starch, although flour contains many other ingredients
such as proteins.) The starch granules then start to enlarge
(think of blowing up a beach ball), trapping water as they grow.
Finally, at temperatures over 150 degrees and up to a point just
below boiling, the rigid structure of the granules breaks up,
creating a spidery web of bonded starch and water molecules.
This mesh prevents the free movement of water molecules and results
in a thick sauce. You probably have also noticed that at this
point, the sauce starts to become clearer. That is because the
starch molecules are no longer packed tightly together--they
are in a looser meshwork after heating--and therefore light is
less likely to be deflected. At temperatures above 200 degrees,
however, the large starch granules start to shrink in size, leaking
starch molecules into the sauce. As these swollen granules deflate,
the sauce becomes thinner.
Although flour is the traditional
thickening agent in French cooking, cornstarch is a more powerful
thickener because it is a purer form of starch. It will also
create a clearer, shinier sauce. The French clarified their sauces
through hours of slow cooking, skimming off the protein as the
sauce simmered, and turning them into perfectly clear, shiny
liquids, which keep their shine even with the addition of flour.
Given the realities of home cooking, this makes no sense and,
therefore, cornstarch is preferable.
The White
Sauce
The most basic sauce is based
on a roux, which is equal volumes of butter and flour whisked
together in a saucepan over heat in order to ameliorate the flavor
of the flour and to remove lumps.
To make a sauce or a base for
a soufflé, for example, hot milk, cream, or stock is added
and, in just a few minutes, the liquid thickens up nicely. The
thickness of the sauce is easily varied by changing the proportion
of roux to liquid. For a thinner sauce, a French chef uses 1
tablespoon each of butter and flour to 1 cup of liquid; for a
medium sauce, 2 tablespoons each; for a thick sauce, 3 tablespoons.
These two basic sauces, a béchamel and a velouté,
are the basis for classic French white sauces.
By adding additional ingredients,
such as cream, cheese-flavored butters, herbs, tomatoes, egg
yolks, curry, white wine, lemon, onions, peppers, etc., or combinations
thereof, chefs made more than 20 different sauces, everything
from an aurore sauce (with tomato purée) to a Mornay sauce
(with cheese). Although these two mother sauces are important
as ingredients in recipes, I find them relatively useless for
sauces. They are too heavy, too thick, and too high in fat. You
do need, however, a béchamel for a soufflé, and
a béchamel or velouté is also used in a classic
lasagna, along with a basic tomato sauce.
Recipe for
Mushroom Purée
You can add a mushroom purée to almost any sauce.
4 cups mushrooms, rinsed and
quartered
1/4 cup chicken or beef stock, preferably homemade
1/4 cup white wine
1 tablespoon butter
1 teaspoon lemon juice
1/2 teaspoon white wine vinegar
1. Purée the mushrooms
with stock and wine in a blender or food processor. Add all ingredients
to a saucepan and simmer until all moisture disappears.
Christopher Kimball is the founder,
publisher, and editor of Cook's Illustrated magazine, and the
author of The Cook's Bible and The Yellow Farmhouse Cookbook
.
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