THE PRODUCTION OF ALCOHOL 215 



turbidity), or, finally, to a strong infection of bacteria (bacterial tur- 

 bidity). In the last-named case turbidity may arise either as a 

 secondary result of ropiness-producing organisms, or may be due to the 

 infection of organisms which do not at the same time produce ropiness. 

 The organisms causing the last-named disease are members of the 

 sarcina group and the disease is known as sarcina-turbidity. It has 

 been shown that these sarcinae, however, may be present in beer in 

 very large numbers without appreciably affecting the quality, and that 

 the malady arises only if certain species are present, and then only 

 under certain conditions. 



Bitterness in beer is caused by the undue development of the " wild " 

 yeast Saccharomyces Pastorianus I. According to Hansen, not only 

 the taste and odour, but also the stability of beer is affected by the 

 presence of this organism in such small quantities as one-fifth of the 

 pitching yeast. 



Other "wild" yeasts of the same class are Saccharomyces Pas- 

 torianus II. and III. These also induce the development of volatile 

 substances which impart to the beer a stronger taste and smell than 

 are produced by the culture yeasts. No. III., if present in an 

 appreciable quantity, also induces turbidity. Although a source 

 of danger, it is claimed that the addition of a small quantity of 

 No. III. to the stock yeast is beneficial when the beer is apt to be 

 opalescent. 



The turning of beer is caused by a bacterial species, known as 

 Saccharobacillus Pastorianus. The beer loses its brilliancy, has a 

 disagreeable smell and taste, and forms a sediment. This species 

 develops in beer only when the latter contains a small amount of hop 

 extract. Its development in beer is prevented when more than 7 per 

 cent, alcohol is present. 



Some members of the acetic-acid bacteria may cause much damage, 

 especially in top-fermentation breweries, where the conditions for their 

 development are more favourable than in bottom-fermentation 

 breweries. By producing acetic acid they cause an unpleasant sour- 

 ness, which greatly detracts from the value of the beer thus affected. 

 The best known are Bacterium aceti, Bact. Pastorianuin, and Bact. 

 Kiitzingianum. As these bacteria are strongly aerobic, beer infected 

 by one or more of them does not become sour if the bottles are well 

 closed and well filled. 



Finally, mention must be made of the ravages that may be caused 

 by the accidental entrance of lactic-acid or butyric-acid bacteria into 

 the mashing- or fermenting-tuns. The butyric-acid bacteria are 



