190 ARTIFICIAL YEAST. 



pend in principle upon the singular property wliich 

 freshly-burnt charcoal has of absorbing gases, and 

 removing coloring and odorous matter generally from 

 substances to which it is added (162). 



464. When, however, there is any great difficulty 

 in procuring fresh and good yeast, it is generally 

 better to use artificial yeast, or to prepare a ferment 

 on purpose ; this is by no means difficult, and then 

 the inconveniences just mentioned are wholly avoided. 

 There are a great number of different ways of making 

 artificial yeast. The object usually is to obtain a 

 quantity of paste or dough in an active state of fer- 

 mentation, and then, by removing the water, to check 

 further change until the ferment is wanted. By 

 carefully washing and pressing beer yeast, so as to 

 separate the moisture as much as possible, it becomes 

 far less liable to spoil than it is in its fresh state. 



465. A tolerably good kind of dry yeast may be 

 made by mixing together a decoction of wheat and 

 bean flour with a small quantity of brewer's yeast ; 

 when the whole is in a state of active fermentation, 

 enough wheat or barley flour is added to form a thick 

 dough, which is then thoroughly kneaded, formed into 

 small cakes, and carefully dried. A very good fer- 

 ment may at any time be obtained from one of these 

 cakes, by crumbling it into warm water, and leaving 

 the mixture a few hours quiet in a warm place. 



466. Yeast may also at any time be prepared 

 direct from malt. When a thick paste or dough of 

 wheat flour is left in a warm place, it soon begins to 



