History of Vinegar-Making 465 



and were shown to have the ability to change alcohol 

 into acetic acid. When the organisms were kept out, this 

 change did not take place. 



Modern knowledge — Within the last fifteen or twenty 

 years, our knowledge concerning acetic-acid fermenta- 

 tion has been enriched by many interesting facts. New 

 species have been gradually added to the two acetic 

 ferments, Mycoderma aceti and Mycoderma Pastorianum, 

 described by Hansen in 1878, until the list includes now 

 at least fifteen distinct organisms. The different organ- 

 isms show characteristic _ 

 variations as to the temper- ««^ ,C 

 atures at which they will ^^i****** 

 grow best; as to develop- ' 

 ment in Hquids of different 

 concentration and compo- •^^i* 

 sition, and as to the amount ^ , . . 



^ . Fig. 71. Acetic-acid bacteria. — land 



of vinegar produced in a 2. Bacteria from sour beer; 



° '^ ^^ X 1,600. (Emmerling.) 3. Bac- 



given time. Henneberg terium acetosum; x 2,000. (Em- 



found, for instance, that 



Bacterium vini acetati showed a moderate growth at 97° 

 Fahr., while Bacterium xylinioides and Bacterium 

 orleanense developed to a very slight extent at this 

 temperature. Similarly, some of the species grew best 

 at 77° Fahr., and others at 86° Fahr. 



It may be concluded, therefore, that the different 

 temperatures prevailing in different vinegar factories 

 will, among other conditions, help to determine which of 

 of the acetic ferments shall predominate. In the same 

 way, it has been found that the various species will be 

 unequally affected by the proportion of alcohol in the 



