STUDIES ON BEEK. 173 



of spring, and thus place himself in a position to meet 

 the demands of consumption without fear of seeing 

 his beer attacked by disease. 



All the diseases of beer, as Pasteur has shown, 

 are caused exclusively by the development of little 

 microscopic fungi, or organised ferments, the germs 

 of which are brought by the dust constantly floating 

 in the air, or which gets mixed with the original sub- 

 stances used in the manufacture. 'By the expression 

 diseases of wort and of beer, I mean,' said Pasteur, 

 ' those serious alterations which affect the quality of 

 these liquids so as to render them disagreeable to the 

 taste, especially when they have been kept for some 

 time, and which cause the beer to be described as 

 sharp, sourish, turned, ropy, putrid.' The wort of beer, 

 after it has been raised to the boiling heat, may, as 

 Pasteur's experiments testify, be preserved indefinitely, 

 even in the highest atmospheric temperatures, when 

 in contact with air free from the germs of the lower 

 microscopic organisms. The must, leavened by the 

 addition of pure yeast, kept free from foreign organ- 

 isms, contains nothing but the alcoholic ferment, and 

 undergoes no other changes than those due to the 

 action of the oxygen, which does not give rise to 

 acidity, putridity, or bitterness. Since the causes of 

 deterioration are the same in beer as in wine, would 

 it not appear as if the action of heat must be the best 



