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Buying Flour
Look for: Tightly sealed bags or boxes. Flours in torn packages or in open
bins are exposed to air and to insect contamination.
Avoid: Stained packages—the liquid that stained the package may have
seeped through into the flour.
Storing Flour
Store all flours in air- and moisture-proof canisters. Whole wheat flours,
which contain the germ and bran of the wheat and are higher in fat than
white flours, may become rancid if exposed to air; they should be used
within a week after you open the package. If you plan to hold the flour
for longer than that, store it in the freezer, tightly wrapped to protect
it against air and moisture. You do not have to thaw the flour when you
are ready to use it; just measure it out and add it directly to the other
ingredients.
Put a bay leaf in the flour canister to help protect against insect
infections. Bay leaves are natural insect repellents.
What Happens When You Cook with Flour
Protein reactions. The wheat kernel contains several proteins, including gliadin and glutenin. When you mix flour with water, gliadin and glutenin
clump together in a sticky mass. Kneading the dough relaxes the long
gliadin and glutenin molecules, breaking internal bonds between individual
atoms in each gliadin and glutenin molecule and allowing the molecules to
unfold and form new bonds between atoms in different molecules. The result
is a network structure made of a new gliadin-glutenin compound called
gluten.
Gluten is very elastic. The gluten network can stretch to accommodate the
gas (carbon dioxide) formed when you add yeast to bread dough or heat a
cake batter made with baking powder or baking soda (sodium bicarbonate),
trapping the gas and making the bread dough or cake batter rise. When you
bake the dough or batter, the gluten network hardens and the bread or cake
assumes its finished shape.
Starch reactions. Starch consists of
molecules of the complex carbohydrates amylose and amylopectin packed into
a starch granule. When you heat flour in liquid, the starch granules
absorb water molecules, swell, and soften. When the temperature of the
liquid reaches approximately 140°F the amylose and amylopectin molecules
inside the granules relax and unfold, breaking some of their internal
bonds (bonds between atoms on the same molecule) and forming new bonds
between atoms on different molecules. The result is a network that traps
and holds water molecules. The starch granules then swell, thickening the
liquid. If you continue to heat the liquid (or stir it too vigorously),
the network will begin to break down, the liquid will leak out of the
starch granules, and the sauce will separate.
Combination reaction. Coating food with
flour takes advantage of the starch reaction (absorbing liquids) and the
protein reaction (baking a hard, crisp protein crust).
Related Links
Flour and
Nutrient
Types of Flour
Medical
Uses and Benefits of Flour
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