THE USEFUL MICROBES 
S3 
“mother of vinegar” is looked at under the 
microscope, it seems to be millions of thread¬ 
like microbes crowded together into a slimy 
mass. These microbes multiply rapidly while 
the acetic acid is being formed from the alcohol, 
and it is their growth which causes the change 
in the cider to take place. 
When vinegar is being made, the freshly 
pressed apple-juice is usually left to stand in a 
cool place for five or six months, to allow the 
alcohol to form, resulting in sour cider. This 
cider, when allowed to stand in a fairly warm 
place, will change into vinegar in about fifteen 
or eighteen months more. Often this change 
is hastened a little by adding some vinegar 
containing the “mother of vinegar” to the fresh 
cider. The cider must be left open to the air, 
for the acetic-acid microbes cannot live and 
multiply, and so change the alcohol into 
vinegar, without a plentiful supply of oxygen, 
the life-giving gas which we get out of the air. 
All of you have seen cakes of yeast. Yeast 
does not remind you of microbes, and so you 
Why is 
vinegar sour? 
