THE PRODUCTION OF ALCOHOL 219 



medium is too acid. The commonest malady is the souring of wine, 



owing to the partial conversion of alcohol into acetic acid by acetic -acid 



bacteria. This result can easily be brought about 



by leaving wine exposed to the air for a few days. 



A tough mucinous skin, composed of millions of 



bacteria very closely packed together, will form 



on the surface of the wine. These bacteria are 



always present in the atmosphere, so that when 



wine is left exposed it is not long before one of FlG 125. -Bacterium 



them drops in and starts multiplying, producing HaiSif* num ' (After 



in a short time millions of its kind. Three of 



these species have been very accurately investigated, viz. Bacterium 



aceti (Fig. 123), Bact. Pastorianum (Fig. 124), and Bact. Kiitzingianum 



(Fig. 125). 



Ropiness is as common a phenomenon in diseased wine as in beer. 

 Kramer has isolated from ropy wines a bacillus with which he was able 

 to induce the same disease in sound white wine. 



The disease known as " turning " of wine results in the assumption 

 of a brown colour by red wines, whilst white wines become turbid and 

 discoloured, and also often assume a dark colour. Two species belong- 

 ing to the genus Micrococcus, which have these effects on wine, have 

 been isolated. 



Finally, lactic acidification ("Zickendwerden") may develop in wine. 

 This is riot an infrequent malady, and is caused by the development of 

 lactic acid, as a result of infection by Bacillus acidi ladici. This species 

 consists of rods which are 1 -0-1-7 p. long and G'3-0'4 /z broad ; they are 

 frequently connected in pairs, rarely in four-membered chains. Wines 

 that in some way have lost their natural acidity are particularly liable 

 to this disease. Thus in 1882 and 1883, the vineyards in the lowlands 

 of Etsch (South Tyrol) were flooded, the grapes becoming incrusted 

 with the carbonates of lime and magnesia. A result of this was that 

 a, portion of the acid in the grapes was neutralised in the process of 

 crushing, with the further result that for a time lactic acidity became 

 a general complaint in the neighbourhood. 



(d) Ginger Beer, This popular beverage is produced in the following 

 manner: A soda-water bottle is filled three parts full of a sugary 

 solution, and into it is placed a lump of ginger and a few lumps of the 

 ginger beer plant. In from 24-28 hours the liquid becomes turbid and 

 bubbles of gas arise. The lumps composing the ginger beer plant are 

 composed of several organisms, two of which cause the fermentation in 

 question. One is a yeast (Saccharomyces pyriformis), and the other 



