THE MANUFACTURE OF VINEGAR. 449 



taining alcohol, is exposed freely to the air, it soon becomes covered with 

 a film, the alcohol disappears, is replaced by acetic acid and the liquid 

 is converted into vinegar. 



This film, the Mycoderma aceti of Pasteur, consists of bacteria coher- 

 ing by means of a glutinous sheath surrounding each cell, forming a 

 zooglea. If the film is undisturbed, the liquid remains clear until 

 converted into vinegar, if disturbed, portions may sink, new films form 

 and finally a large gelatinous zoogleic mass, "the mother of vinegar," 

 may form in the liquid. 



Sometimes, especially on liquids containing sugar and large amounts 

 of alcohol, such as sweet wines, the film formed consists, not of bacteria, 

 but of a yeast-like fungus, Mycoderma vini.- 



Wines which have been sterilized, often remain without acetifying 

 for a considerable time. Those containing traces of sulphurous acid 

 acetify slowly and with difficulty. Ordinarily at warm temperatures, 

 exposed wines develop a bacterial film very rapidly owing to the almost 

 constant presence of some acetic bacteria in all wines. 



Hansen was the first to show that the vinegar bacteria included more 

 than one species. He isolated and described three species concerned 

 with the spontaneous souring of beers. Later it was shown by A. J. 

 Brown, Henneberg and others that several other species commonly 

 occurred in vinegar factories and that many more were capable of pro- 

 ducing acetic acid in small amounts. The species which have been 

 most thoroughly studied and which seem to occur most usually in vinegar 

 factories are Bact. aceti, Bact. pasteurianum, Bact. kutzingianum, Bact. 

 xylinum, short descriptions of which follow: 



Bacterium aceti (Kutzing), Hansen. This species consists of rods about i// or 2fj. 

 in length, somewhat constricted in the middle and lying in parallel chains in 

 the surface film. This film is moist, smooth, veined, and forms in about twenty- 

 four hours at 34. On wort gelatin, it forms gray, waxy, raised colonies which are 

 usually round, with unbroken edges but sometimes star-shaped and consisting of sep- 

 arate rod-shaped cells. 



Bacterium pasteurianum, Hansen. The cells of this species are somewhat larger 

 than those of aceti and more commonly produce thread-like and swollen involution 

 forms. The film is dry and soon becomes wrinkled. Colonies on wort gelatin are 

 smaller than those of aceti, rugose, and the cells retain their arrangement in chains. 

 The mucilaginous sheath is stained blue with iodine-potassium iodide solution, in this 

 differing from Bact. aceti (Fig. 88). 



Bacterium kutzingianum, Hansen. 'The cells resemble those of Bact. aceti, but are 

 usually free or in pairs. The film resembles that of Bact. aceti but has a tendency to 



2Q 



