Sauces and puddings can be thickened by
using various ingredients, including eggs, gelatin, and starches, such as
flour, cornstarch, arrowroot, or rice flour. These thickeners may be used
to lightly thicken a mixture, as for a sauce, or to produce an item that
is firmly set.
The quantity and type of thickener, as well
as the amount of stirring or other manipulation, will determine the
finished product's properties. For example, if a custard is cooked over
direct heat and stirred constantly, the result will be a sauce that pours
easily. The same custard cooked in a bain-marie with no stirring at all
will set into a firm custard that can be sliced.
Arrowroot and cornstarch are generally
preferred for thickening sauces, puddings, and fillings where a
translucent effect is desired. If these thickeners are to be diluted
before incorporation with other ingredients, they should be mixed with a
small amount of a cool liquid.
Flour is commonly used to thicken foods. In
order to prevent lumping, the flour and sugar are often stirred together
before they are combined with the liquid. Flour-thickened sauces are also
often additionally thickened and enriched with eggs. The eggs must be
tempered to prevent the sauce from curdling. Eggs (whole eggs or yolks)
may be used either alone or in conjunction with other thickeners. As the
egg proteins begin to coagulate, the liquid becomes trapped in the network
of set proteins, producing a texture, in which the sauce will coat the
back of a spoon when the spoon is dipped into the sauce and withdrawn.
Gelatin, when added in the desired amount,
can produce light, delicate foams that are firmly set. Such foams will
retain a mold's shape and can be sliced. Gelatin is an animal protein
found in bones. it is this protein that causes stock to gel as it cools.
Gelatin powder or sheets are frequently used for a variety of bakeshop
items. Before use, gelatin must first be softened in a cool liquid. Once
the gelatin has absorbed the liquid, it is then gently heated to melt the
crystals. This is accomplished either by adding the softened gelatin to a
hot mixture, such as a hot custard sauce, or by gently heating the gelatin
over simmering water.