VINEGAR-MAKING 233 
mixing the dough, is also recommended as a remedy, based upon 
the fact that lactic acid bacteria will check the growth of other 
organisms. 
VINEGAR-MAKING 
Vinegar is used both as a direct condiment to give relish to 
foods and as a preservative, as in the manufacture of pickles. It is 
made on a large scale in vinegar factories and on a small scale on 
farms. It is always made from some weak alcoholic solution, like 
cider, weak wine, or beer, each locality using as a source the alco- 
holic solution most easily obtained. The essential part of the 
process is the chemical union of the alcohol with oxygen from the 
air, by which it is converted into acetic acid. Such a simple oxida- 
tion can be brought about by a purely chemical process. As long 
ago as 1721, Davy discovered that platinum-black, or finely di- 
vided platinum, when mixed with alcohol, causes an active union 
with oxygen to take place, which results in the production of acetic 
acid. 
When vinegar is formed in the usual way, a brownish gelatinous 
mass called ‘“‘mother of vinegar’ is formed, and for a time it 
was believed that this mother of vinegar acted like the platinum- 
black, “condensing”? the oxygen, and thus causing a chemical 
union. But the error of this conclusion was later shown. (1) The 
ordinary vinegar fermentation is stopped by the accumulation 
of acid, and it will not occur at all if the amount of acetic acid 
in the solution be more than 14 per cent. The formation of 
acid by platinum-black is entirely uninfluenced by such an 
accumulation. (2) The formation of the acid in vinegar is most 
abundant at about 95°F., diminishing rapidly at higher tem- 
peratures, and may in itself produce so much heat as actually 
to ignite the alcohol. (3) Later the production of acetic acid 
by the growth of pure cultures of certain bacteria showed vinegar- 
making to be a true fermentation. 
