Heat. Increasing the temperature may bring about a greater or a lesser
degree of dispersion. The heating of water increases its dispersion. The dis-
persion of fat globules in milk is increased by the application of heat to
DISPERSION BY ALKALIES 5
the milk, but when proteins are coagulated by heat the degree of dispersion
is decreased.
Mechanical dispersion. Beating of a food is a mechanical means of
bringing about a greater or a lesser degree of dispersion. In cookery, stir-
ring may bring about more uniform distribution of particles in a food,
like white sauce. But even this may prevent lumping or clumping and thus
is a means of bringing about dispersion, just as beating a curdled custard
is a mechanical means of bringing about a greater degree of dispersion of
a suspension, but although it reduces the size of the curds it does not reduce
them enough to change the suspension to the colloidal state. Homogenization
of milk or cream is a mechanical means of increasing the dispersion of fat
particles. Beating an egg white is a mechanical means of lessening the
degree of dispersion, as it brings about partial coagulation of the egg white
in the cell walls surrounding the air bubbles.
Dispersion by acids. The addition or the development of acid in
preparation of food may be a chemical means of bringing about a greater or
a lesser degree of dispersion. For instance, the development of acid during
the fermentation of bread brings about greater dispersion of the gluten.
The addition of acid to whole egg tends to curdle the egg or bring about a
lessened degree of dispersion. If a large enough quantity of acid is added,
the degree of dispersion may be increased after passing through a zone
of lesser dispersion. The explanation of the different effects of acid on the
gluten and on the egg proteins depends upon the isoelectric point of the
gluten and the egg protein and the degree of acidity developed. This will
be considered later.
Dispersion by alkalies. The addition of alkalies may also tend to
bring about a greater or a lesser degree of dispersion. In quick breads and
cakes the addition of soda in excess of the amount required to neutralize
the acidity of the mixture may bring about increased dispersion of the
gluten particles, which results in a definite grain or crumb.
The different methods of bringing about a lesser or a greater degree of
dispersion are applicable to all food products. In some cases the effect may
be modified by other factors. It is interesting to trace these through dif-
ferent classes of food products. If alkali is taken as an example, its effects
on some foods may be cited. The alkalies, hydroxides of ammonia, sodium,
and potassium or their basic salts are the ones considered. Calcium and
magnesium salts may have different effects.
Sucrose is little affected by alkalies if they are not stronger than those
ordinarily used in cookery. But when alkalies are added to the mono-
saccharid sugars they bring about decomposition. The sugar in solution is
in the molecular state, and the alkalies cause increased dispersion, even
though the sugar and its decomposition products both remain in molecular
dispersion. The properties of the decomposition products are different
from those of the original sugar.
Vegetables and fruits are softened by the addition of alkalies during
6 RELATION OF COOKERY TO COLLOID CHEMISTRY
Page 6
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Heat. Increasing the temperature may bring about a greater or a lesser
degree of dispersion. The heating of water increases its dispersion. The dis-
persion of fat globules in milk is increased by the application of heat to
DISPERSION BY ALKALIES 5
the milk, but when proteins are coagulated by heat the degree of dispersion
is decreased.
Mechanical dispersion. Beating of a food is a mechanical means of
bringing about a greater or a lesser degree of dispersion. In cookery, stir-
ring may bring about more uniform distribution of particles in a food,
like white sauce. But even this may prevent lumping or clumping and thus
is a means of bringing about dispersion, just as beating a curdled custard
is a mechanical means of bringing about a greater degree of dispersion of
a suspension, but although it reduces the size of the curds it does not reduce
them enough to change the suspension to the colloidal state. Homogenization
of milk or cream is a mechanical means of increasing the dispersion of fat
particles. Beating an egg white is a mechanical means of lessening the
degree of dispersion, as it brings about partial coagulation of the egg white
in the cell walls surrounding the air bubbles.
Dispersion by acids. The addition or the development of acid in
preparation of food may be a chemical means of bringing about a greater or
a lesser degree of dispersion. For instance, the development of acid during
the fermentation of bread brings about greater dispersion of the gluten.
The addition of acid to whole egg tends to curdle the egg or bring about a
lessened degree of dispersion. If a large enough quantity of acid is added,
the degree of dispersion may be increased after passing through a zone
of lesser dispersion. The explanation of the different effects of acid on the
gluten and on the egg proteins depends upon the isoelectric point of the
gluten and the egg protein and the degree of acidity developed. This will
be considered later.
Dispersion by alkalies. The addition of alkalies may also tend to
bring about a greater or a lesser degree of dispersion. In quick breads and
cakes the addition of soda in excess of the amount required to neutralize
the acidity of the mixture may bring about increased dispersion of the
gluten particles, which results in a definite grain or crumb.
The different methods of bringing about a lesser or a greater degree of
dispersion are applicable to all food products. In some cases the effect may
be modified by other factors. It is interesting to trace these through dif-
ferent classes of food products. If alkali is taken as an example, its effects
on some foods may be cited. The alkalies, hydroxides of ammonia, sodium,
and potassium or their basic salts are the ones considered. Calcium and
magnesium salts may have different effects.
Sucrose is little affected by alkalies if they are not stronger than those
ordinarily used in cookery. But when alkalies are added to the mono-
saccharid sugars they bring about decomposition. The sugar in solution is
in the molecular state, and the alkalies cause increased dispersion, even
though the sugar and its decomposition products both remain in molecular
dispersion. The properties of the decomposition products are different
from those of the original sugar.
Vegetables and fruits are softened by the addition of alkalies during
6 RELATION OF COOKERY TO COLLOID CHEMISTRY