Mr. Fownes on the Preparation of Artificial Yeast. 353 



Boutron and Fremy on the formation of lactic acid, serves to 

 solve this difficulty, as it will doubtless many others of far 

 greater magnitude and importance. It has been shown that 

 " the kind of chemical change going on in the decomposing azo- 

 tized body or ferment, determines the kind of decomposition 

 which shall occur in the neutral ternary substance, subject to 

 its influence;" that diastase, for example, according to its 

 peculiar condition, whether fresh from the germinated grain, 

 slightly putrefied, or in a still more advanced state of that 

 change, possesses the singular power, in the first case, of 

 changing starch into dextrin, and ultimately into grape sugar; 

 in the second, of causing the conversion of sugar into lactic 

 acid ; and in the third and last, of exciting the vinous fermen- 

 tation. 



Now if common wheaten flour be mixed with water to a 

 thick paste, and exposed, slightly covered, to spontaneous 

 change in a moderately warm place, it will be observed to 

 run through a series of changes which seem very closely to 

 resemble those described by MM. Boutron and Fremy in the 

 case of diastase. 



About the third day of such exposure it begins to emit a 

 little gas, and to exhale an exceedingly disagreeable sour odour, 

 much like that of stale milk ; after the lapse of some time this 

 smell disappears, or changes in character, the gas evolved is 

 greatly increased, and is accompanied by a very distinct and 

 somewhat agreeable vinous odour : this will happen about the 

 sixth or seventh day, and the substance is then in a state to 

 excite the alcoholic fermentation. 



A quantity of brewers' wort is next to be prepared in the 

 usual manner, by boiling with hops ; and when cooled to 90° 

 or 100°, the decomposed dough before described, after being 

 thoroughly mixed with a little tepid water, is added to it, and 

 the temperature kept up by placing the vessel in a warm si- 

 tuation. After the lapse of a few hours active fermentation 

 commences; abundance of carbonic acid, having its usual 

 agreeable pungent smell, is disengaged, and when the action 

 is complete and the liquid clear, a large quantity of excellent 

 yeast is found at the bottom, well adapted to all purposes to 

 which that substance is applied. 



In one experiment the following materials were used : — a 

 small handful of ordinary wheat flour was made into thick 

 paste with cold water, covered with paper, and left seven days 

 on the mantel-shelf of a room where a fire was kept all day, 

 being occasionally stirred: at the end of that period three quarts 

 of malt were mashed with about two gallons of water, the infu- 

 sion boiled with the proper quantity of hops, and when suffi- 



