132 BACTERIA, YEASTS, AND MOLDS 



quantities as a condiment and preservative. As ordinarily 

 made it is simply a product of bacterial growth. The 

 basis of vinegar is acetic acid, and this is produced from 

 alcohol by certain changes brought about in it through 

 the action of microorganisms. The source of vinegar is 

 always some weak alcoholic solution, commonly cider or 

 weak wine; but any liquid that contains a moderate 

 quantity of alcohol may be a source of vinegar. This 

 material is caused to undergo a chemical change which 

 converts the alcohol into acetic acid, and when this occurs 

 it becomes vinegar. 



* The change of the alcohol into acetic acid is brought 

 about by the presence of a material, a brownish, felted, 

 slimy mass, which increases in amount as the vinegar is 

 made, and upon whose presence the conversion of alcohol 

 into vinegar seems to depend. This has long been known 

 as mother of vinegar. Good vinegar will always contain such 

 mother. The study of this mother of vinegar shows it 

 to be a mass of bacteria (Fig. 61). They are crowded 

 together in countless millions to form this slimy mass, 

 and during the production of the vinegar multiply rapidly 

 and finally become excessively numerous. The growth of 

 the bacteria produces the change in the alcohol which con- 

 verts it into acetic acid. The formation of common vinegar 

 is therefore due to the development of microorganisms. 

 Some types of a cheap product are made by a chemical 

 process, but all good table vinegar is produced by bacteria. 

 A knowledge of the manufacture of vinegar is to-day a 

 matter of little importance in the household, for the mate- 

 rial is commonly made either in large factories or in a 

 farmer's cellar. The housewife is simply concerned in 



