When vegetables are placed in brine the juices and soluble material
contained in them are drawn out by the force known as osmosis.
The fermentable sugar present in all fruits and vegetables, which is one
of the soluble substances extracted by osmotic action, serves as food
for the lactic-acid bacteria which break it down into lactic acid and
certain volatile acids. In some vegetables, like cucumbers and cabbage,
where the supply of sugar is ample and other conditions are favorable to
the growth of the lactic bacteria, a decided acid formation takes place,
constituting a distinct fermentation. The acid brine thus formed acts
upon the vegetable tissues, bringing about the changes in color, taste,
and texture which mark the pickled state.
As a rule, a solution of salt is used, although some vegetables quickly
give up enough moisture to convert dry salt into brine. Salt also hardens
or makes firm the vegetables placed in brine and checks the action of
organisms which might otherwise destroy the plant tissues.
Cabbage is well preserved in its own brine in the form of sauerkraut.
Other vegetables and some fruits may, under certain conditions, be
economically preserved by brining. As a rule, however, canning is
preferable for these products, because food values and natural flavors
are better preserved by that method. Lack of time, a shortage of cans, or
an oversupply of raw material may justify the preservation of vegetables
other than cucumbers and cabbage by curing in brine.