222 BACTERIOLOGICAL METHODS 



1. Gluten turbidity, due to the precipitation of protein 

 substances. 



2. Starch turbidity, due to the presence of unchanged starch. 



3. Yeast turbidity, due to a high content of yeast cells. 

 If wild yeasts are the cause of the turbidity then there may be 

 noticeable a bad taste and bad odor. 



4. Bacterial turbidity, due to the development of bacteria. 

 In this case there may be noticeable bad odor, bad taste and 

 ropiness. 



5. Sarcina turbidity, caused by the members'^of the sarcina 

 group. Unless certain species are present in large numbers the 

 beer may not be appreciably affected in quality. It must be 

 remembered that some of the sarcinas cause disturbances in 

 gastric digestion. 



3. "Wines. — Wine is grape juice which has undergone alcohoUc 

 fermentation through the action of yeast organisms. To enter 

 into the details of wine production is not necessary. Wines vary 

 in the amount of alcohol (8 to 16 per cent.) which they contain, 

 in color, in taste, in the amount of unchanged or added sugar, 

 in the amount of acid, etc. Saccharomyces ellipsoides is the most 

 common yeast concerned in the alcoholic fermentation of grape 

 juice. Wine diseases are frequently met with and are not unlike 

 those of beer. Ropiness, turning and lactic acidiiication are 

 perhaps the most common, induced by bacilli and cocci. It 

 may be stated that the greater natural acidity of wines in general 

 tends to retard or check bacterial invasion. Bacterial invasion is 

 also in a measure checked by the greater alcohol content of wines 

 over that of beers. Souring of wine is the most common malady, 

 induced by acetic acid bacteria which reduce much of the alcohol 

 into acetic acid. A tough membranous scum forms on the 

 surface of the wine, composed of a nearly pure culture of the 

 acidifying bacteria. Bacterium (Mycodernia) aceti, B. pastorianum 

 and B. kuizingiauum are the most common of the acid formers 

 and the three species appear to be very closely related. Souring of 



