417 



formed into alcohol and carbonic acid gas, generate 71 calories, or 

 enough heat to raise the temperature of a must containing 20 per 

 cent, sugar and fermenting completely to 128deg. Fahr., provided 

 all the heat were accumulated in the fermenting vessel without loss. 



This fact, demonstrated by theory, does not, however, occur in 

 practice. Several sources of leakage tend to reduce that temper- 

 ature, such as the radiation of heat through the staves or sides of 

 the vat, the evaporation which takes place from the surface of the 

 liquid, the bursting on the surface of the hot bubbles of the 

 carbonic acid gas, which escapes through the air. Were it not for 

 these sources of diffusion of heat generated,, the yeast would soon 

 be paralysed or killed, and the vat would get " stuck." 



What that amount of heat is, at any given moment, within the 

 mass in fermentation, can thus be expressed in the terms of a 

 mathematical equation : 



The temperature of the fermenting mass is equal to that of 

 the grapes at the time of crushing, plus that due to the heat 

 evolved during the fermentation, less that lost by radiation and 

 evaporation. 



It is a matter of common observation that, unless checked, the 

 temperature of a 600 or 700- gallon vat in Australia rises from 

 20 to 25 F. during fermentation. In other words, grapes crushed 

 at 65 F. will rise in the vat, if the temperature be unchecked, to 

 80~ or 85 F., whereas the same grapes vatted at a temperature of 

 75 F. will rise to about 95 or 100 F. As that temperature is 

 decidedly injurious to the yeast of wine fermentation (saccharomyces 

 ellipsoideus) , and on the other hand is favourable to bacterial life, 

 or the life of those microbes which are the cause of disease in wine, 

 it is obvious that, where no artificial means are at hand to control 

 the excess of temperature, the grapes should be vatted when cool 

 only. 



It is therefore essential, whilst the grapes are fermenting, to 

 ascertain, by means of frequent testings with the thermometer, 

 what the temperature is inside the vat. 



The elliptic yeast does its best work between the temperatures 

 of 75 and 90 F. Below 75 the 8. pastorianus or the 8. apiculalus, 

 which, at best, are but very poor kinds of ferments, thrive 

 best ; above 95 the ferments of acetic acid and of lactic acid play 

 an active part, the conversion of sugar into alcohol ceases through 

 the death of the yeast of wine fermentation, and the vat gets 

 " stuck," with a proportion of unfermented wine still left in it. 

 During the course of a sickly fermentation, not only does the work 

 done by sickly yeast plants fall short, both as regards quality and 

 quantity, with what healthy yeast plants would do, but the same 

 circumstances which have brought about that unsatisfactory state 

 of things, i.e., excess of heat, being favourable to bacterial life, it 



