60 
Pasteur and his Work, 
The manufacture of vinegar is largely carried on at Orleans, 
being one of the staple industries of that city, and to this 
Pasteur devoted his attention. When wine becomes sour — as in 
bottles to which, through faulty corking, air has obtained access 
— it is noticed that the oxygen which was originally in it has dis- 
appeared, and that nitrogen has replaced it ; while the alcohol 
has also vanished, and in its stead is acetic acid or vinegar. The 
presence of air is necessary for this change, and before Pasteur 
took up the subject, the ordinary method of manufacturing 
vinegar was to expose barrels half-full of vinous fluid to the air, 
and at a certain temperature ; the acetic fermentation was set 
up and carried on, and every week a small quantity of vinegar 
was drawn from the barrel and an equal amount of new wine 
added. This was a slow and a somewhat unsatisfactory process, 
inasmuch as some months elapsed before fermentation was 
fully established. The notion was that the alcohol in the fer- 
menting wine was changed into vinegar, by the chemical 
influence of the oxygen in the air, acting in the presence of 
dead albuminoid matter. But Pasteur proved that this matter 
had no influence in the change ; for though alcohol be mixed 
with pure water until it is reduced to the strength of wine, 
and exposed to the air, it will show no trace of vinegar ; yet 
if some wine be put in a bottle, and this be sealed and then 
heated to about 140° Fahr., the same result will be noted ; while 
if it be not heated it will become sour. More than this, if the 
bottle which has been subjected to the high temperature, be 
afterwards opened and the air admitted, the wine sours. In 
addition to this demonstration, and to still further show that 
the dead albuminoid matter of the chemists had nothing to 
do with the conversion of alcohol into acetic acid, Pasteur 
removed all traces of albuminous substance from wine, and in- 
troduced to it a small quantity of phosphates of ammonia, potash, 
and magnesia ; the vessel was then sealed up and laid by for some 
time. When again examined, the alcohol had become vinegar. 
The real cause of the change was the presence of a minute 
fungus — the Mijcoderma aceti — known for generations as the 
" flower of vinegar," which is always seen on the surface of 
wine undergoing the change, but which Liebig, who knew it, 
considered a mere coincidence. The formation of vinegar is 
always preceded by the development, on the surface of the wine, 
of this very minute plant, which, when magnified, appears as 
an extremely fine constricted body ; its accumulation constitutes 
sometimes a scarcely perceptible scum, at other times a thin 
wrinkled film, unctuous to the touch, because of the various fatty 
matters it contains. It has the singular property of condensing 
considerable quantities of oxygen, and of fixing this gas upon the 
alcohol, thereby transforming it into acetic acid. But like the 
