VINEGAR 
6i 
is only very slightly acid, but if allowed to stand for 
a while it becomes sharply acid. This acetic acid 
is the result of bacterial growth and finally turns the 
sweet, pleasant drink into hard cider or cider vinegar. 
Fig- 37- 
The process of change is a complex one, due to 
both chemical and bacteriological agencies. When the 
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FIG. 37. BACTERIA WHICH MAKE ACETIC ACID AND VINEGAR. 
(After Conn.) 
wild yeasts have brought about the alcoholic fermenta¬ 
tion of the sweet apple juice certain bacteria take up 
the work and produce acetic acid in a weak solution 
which we know as vinegar. There are different spe¬ 
cies capable of producing acetic acid of different 
strengths and under different conditions. What is 
known as the mother-of-vinegar is a dense mass of 
bacteria—a true zoogloea form. Fig. 38. 
Sugar to 
Acetic Acid 
