220 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX. 
once started, may continue in operation some six or eight years con- 
tinuously, but eventually it becomes so filled with tartar and mother 
of vinegar that it must be cleansed. 
Shortly after the process of vinegar-making is started a skin of 
the vinegar organisms grows on the surface, soon covering the 
whole. Its action causes the alcohol to unite with oxygen from the 
air, thus producing acetic acid. The bacteria in this method grow 
chiefly on the surface of the liquid, and they develop luxuriantly 
during the process. The oxidation does not always stop at the 
formation of acetic acid, but is sometimes carried further so as to 
split up the alcohol into simpler molecules. This results in a loss, 
and is one of the difficulties to be met with in the manufacture of vin- 
egar. This loss, though sometimes considerable, is generally not 
great, for the accumulation of acetic acid will soon stop the growth 
of the organisms. Different species of the organisms can endure 
different amounts, but when the acetic acid has reached 14 per cent, 
the bacteria are never able to produce any more. 
The Quick Process. A second process of vinegar-making, known 
as the "quick process," does not, at first sight, appear to be caused 
by microorganisms. This process consists simply in an intimate 
mixture of alcohol with air by means of shavings. A mass of 
shavings is placed in tall vessels and thoroughly moistened with an 
alcoholic solution. Then the whole is inoculated with a little warm 
vinegar followed by alcohol. The vinegar thus added starts the 
process, and in a few hours new vinegar is produced. Alcohol is 
now added at the top, slowly but continuously, and it percolates 
through the shavings and appears at the bottom as vinegar. Such 
a process seems at first to be more like a chemical phenomenon than 
a fermentation induced by microorganisms. But it does not start 
until a little warm vinegar has been added to the mixture, and such 
vinegar will be sure to contain bacteria. This, of course, suggests 
that the microorganisms, thus added, spread through the shavings, 
grow rapidly, and soon induce the oxidation. Indeed, it has been 
proved that, if the growth of the fungi is prevented in such a mixture, 
no vinegar is formed. The shavings simply furnish a large surface 
for the spreading out of the organisms. Hence, the quick vinegar 
