254 FKAG-MENTS OF SCIENCE. 



time the unintoxicating grape-juice is converted into 

 intoxicating wine. Here, as in the case of the cherries, 

 the fermentation is spontaneous in what sense sponta- 

 neous will appear more clearly by-and-by. 



It is needless for me to tell a Glasgow audience that 

 the beer-brewer does not set to work in this way. In 

 the first place the brewer deals not with the juice of 

 fruits, but with the juice of barley. The barley having 

 been steeped for a sufficient time in water, it is drained 

 and subjected to a temperature sufficient to cause the 

 moist grain to germinate; after which, if is completely 

 dried upon a kiln. It then receives the name of malt. 

 The malt is crisp to the teeth, and decidedly sweeter to 

 the taste than the original barley. It is ground, mashed 

 up in warm water, then boiled with hops until all the 

 soluble portions have been extracted ; the infusion thus 

 produced being called the wort. This is drawn off, and 

 cooled as rapidly as possible ; then, instead of abandon- 

 ing the infusion, as the wine-maker does, to its own 

 action, the brewer mixes yeast with his wort, and places 

 it in vessels each with only one aperture open to the 

 air. Soon after the addition of the yeast, a brownish 

 froth, which is really new yeast, issues from the .aperture, 

 and falls like a cataract into troughs prepared to receive 

 it. This frothing and foaming of the wort is a proof 

 that the fermentation is active. 



Whence comes the yeast which issues so copiously 

 from the fermenting tub ? What is this yeast, and how 

 did the brewer become possessed of it ? Examine its 

 quantity before and after fermentation. The brewer 

 introduces, say 10 cwts. of yeast ; he collects 40, or it 

 may be 50, cwts. The yeast has, therefore, augmented 

 from four to five fold during the fermentation. Shall 

 we conclude that this additional yeast has been sponta- 

 neously generated by the wort ? Are we not rather re- 



