THE MICROBIOLOGY OF ALCOHOL PRODUCTS ,529 



Diseases of Beer 



Beer may show defects due to imperfections in the raw material or 

 in the methods of manufacture. These are principally abnormal flavors 

 and lack of clearness. 



The diseases properly so called are due to wild yeasts or to bacteria. 

 The disease-producing yeasts may be derived from the starter, from the 

 vessels with which the beer comes in contact, or from the air. They 

 develop most commonly during the secondary fermentation or in the 

 bottle. Some may produce a disagreeable bitterness {S. paskurianus 

 I) or other unpleasant flavor {S. fcetidus); many produce a persistent 

 cloudiness (5. ellipsoideus, S. apiculatus, S. exiguus, S. anomalus). 

 They are to be combated by preventing contamination, by proper 

 attenuation and by pasteurizing. 



Bacterial diseases were more common before effective methods of 

 purifying yeasts were known. 



Many forms of lactic bacteria may affect the beer, rendering it acid 

 and cloudy. They occur principally where the temperature is allowed 

 to become too high and where proper care in the cleaning and steril- 

 ization of utensils is not exercised. 



Acetic bacteria may occur under the same conditions and give a 

 taste of vinegar to the beer. They are more common in top fermented 

 beers. 



Various forms of Sarcina may cause persistent cloudiness, acid, 

 unpleasant flavors or both. This contamination iftay be from the air 

 or the water and is relatively common. Their growth is most rapid 

 at 16° to 20° and is retarded by the antiseptic properties of hops. 



Several kinds of bacteria, bacilli, cocci and sarcinae may cause the 

 beer to become slimy or viscid and injure the flavor. This trouble is 

 particularly common in spontaneously fermented beer. 



Wort and beer, being organic solutions containing very little acidity, 

 are favorable media for the growth of bacteria, many forms of which 

 may cause trouble. With modern methods of using pure yeastj 

 cleanliness and the pasteurization of bottled beer, diseases can be 

 controlled. 



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