164 C. A. WATKINS ON YEAST AND OTHER FERMENTS. 



mentation lias been stopped, a very disagreeable effect is produced ; 

 the beer is not acetified, but the flavour is entirely changed ; it is 

 unpalatable, and the brewers call it yeast-bitten. 



Now I am not in a position to throw any light on this change ; 

 but if stale yeast be examined with the microscope, there will be 

 found interspersed among the ordinary cells a large number of 

 minute globular bodies, which are generally in motion ; and I have 

 also noticed a larger proportion of short, straight vibrio-like bodies, 

 than are to be found in yeast during active fermentation. 



Whether these organisms produce the disagreeable effects referred 

 to, I am unable to say, and merely point to them as one of the 

 changes which take place in yeast when left to itself. 



Diastase is a ferment, which has the property of converting 

 starch into sugar, by causing it to assimilate the elements of water 

 without evolving any gaseous products. < N - 



The transformation is represented thus : — 



Starch. Water. Sugar. 



CHO + 2HO = CHO 

 12 10 10 12 12 12 



Diastase is extracted from malt by soaking it in water, in which, 

 at moderate temperature, it is soluble ; it may be taken as the type 

 of the ferments produced in all germinating seeds — for as all seeds 

 contain starch, which must be rendered soluble in the form of sugar 

 before it can become food for the embryo — so they all contain some 

 azotised matters as albumen, gluten, &c, which are capable of 

 passing into the form of a ferment, allied to diastase. 



The action of diastase on starch is so well described in all 

 chemical works — which treat of the vegetable products — that it 

 seems strange anyone should attribute the conversion of starch into 

 sugar, during germination, to any other cause, without assigning 

 some sound reason. Yet, in a popular book by Dr. Carpenter, on 

 " Vegetable Physiology," published a few years ago, he says : — 

 " Starch differs but little from sugar, in chemical composition, 

 except in containing one additional proportion of carbon. When 

 germination commences, oxygen is absorbed by the seed in the 

 substance of which it combines with the carbon that is to be set 

 free from it ; and a large quantity of carbonic acid is then given 

 forth again to the air, whilst, in the same proportion, the starch is 

 converted into sugar." 



This implies that the conversion of the starch into sugar, and 

 the evolution of C O 2 gas in germination, are the results of the 



