VINEGAR-MAKING. 2 17 



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, i. 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 temperatures, 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. 



The Vinegar Organism. The mother of vinegar is a soft, 

 semi-solid mass, commonly forming a scum on the surface of the 

 fermenting alcohol. Vinegar is not formed if this material be lack- 

 ing, and a very small bit placed on the surface of an alcoholic solution 

 soon extends itself and covers the whole surface, inducing an active 

 acetic acid formation. This mother of vinegar proves to be a mass 

 of microorganisms. It was first named Mycoderma by Persoon, 

 who studied it in 1812, without having any suspicion that the skin 

 was the cause of the acetic acid. Later, Kiitzing, showed that this 

 skin was made of numerous minute, living organisms, and positively 

 asserted that they were the cause of the acetic fermentation. 

 But the chemist Liebig checked the advance of discovery by his own 

 theories of fermentation, which regarded the whole class of phe- 

 nomena as chemical processes. 



It was eventually Pasteur who demonstrated that the process is 

 really a fermentation due to the activity of the microorganisms in the 

 mother of vinegar. An examination of this material shows it to be 

 made of a mass of bacteria. Pasteur used for them the name 

 Mycoderma aceti, but he did not study them sufficiently to show 

 what they were, although he demonstrated their relations to vinegar- 

 making. Hansen later proved they were bacteria, and showed 

 that in the different samples of "mother" there are several varieties. 

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