which take place in these
different steps are:

sucrose dextrose levulose
(1) C_{12}H_{22}O_{11} + H_{2}O = C_{6}H_{12}O_{6} + C_{6}H_{12}O_{6};

dextrose alcohol
(2) C_{6}H_{12}O_{6} = 2 C_{2}H_{5}OH + 2 CO_{2};

alcohol acid
(3) C_{2}H_{5}OH + 2 O = HC_{2}H_{3}O_{2} + H_{2}O.

[Illustration: FIG. 52.--ACETIC ACID FERMENTS. (After KOeNIG.)]

The acetic acid organism, _Mycoderma aceti_, can work only in the
presence of oxygen. It is one of the aerobic ferments, and is present in
what is known as the "mother" of vinegar and is secreted by it. When
vinegar is made in quantity, the process is hastened by allowing the
alcoholic solution to pass through a narrow tank rilled with shavings
containing some of the ferment material, and at the same time air is
admitted so as to secure a good supply of oxygen. When vinegar is made
by allowing cider or wine to stand in a warm place until the
fermentation process is completed, a long time is required--the length
of time depending upon the supply of air and other conditions affecting
fermentation.

In some countries malt vinegar is common. This is produced by allowing a
wort made from malt and barley to undergo acetic acid fermentation,
without first distilling the alcohol as is done in the preparation of
spirit vinegar. In various European countries wine vinegar is in general
use and is made by acetification of the juice of grapes. Sometimes
spirit vinegar is made from corn or barley malt. Alcoholic fermentation
takes place, the alcohol is distilled so that a weak solution remains,
which is acetified in the ordinary way. Such a vinegar can be produced
very cheaply and is much inferior in flavor to genuine wine or cider
vinegar.

Vinegar, when properly made, should remain clear, and should not form a
heavy deposit or produce any large amount of the fungous growth,
commonly called the "mother" of vinegar. In order to prevent the vinegar
from becoming cloudy and forming deposits, it should be strained and
stored in clean jugs and protected from the air. So long as air is
excluded further acetic acid fermentation and production of "mother" of
vinegar cannot take place. When the vinegar is properly made and the
fermentation process has been completed, the acid already produced
prevents all further development of acetic acid ferments. When vinegar
becomes cloudy and produces deposits, it