194 GRAPE CULTURE AND WINE-MAKING. 



liquor, when the highest degree of heat has been attained about 

 nine tenths of the sugar has been decomposed. 



When the sugar has been decomposed, or the fermentation be- 

 gins to subside on account of the lack of yeast or its inefficiency, 

 the formation of air-bubhles decreases, as less sugar becomes resolved 

 into carbonic acid and alcohol. These bubbles, -which had formed 

 a kind of foam upon the surface, gradually disappear by bursting, 

 and are replaced by few new ones. The falling of the foam now 

 begins by the formation of air-holes and rents ; and also the burst- 

 ing of the surface, as the solid parts, which had hitherto been kept 

 floating by the foam, now follow the law of gravit}^, and sink back 

 into the fluid. At the same time the decrease of heat begins, as a 

 natural consequence of the lessened development of carbonic acid. 

 The cessation of the inner commotion soon follows; in consequence 

 of which, the heavy parts of the liquid are precipitated to the bot- 

 tom, while the lighter ones swim on the surface. These latter 

 consist mainly of the yeast, a part of which had been used up in 

 the fermentation, while a part had been formed during the process 

 from the gum and vegetable albumen contained in the juice. 



The result of these various processes is the clearing of the fluid, 

 especially of the middle portion of it. This clearing may be con- 

 sidered as a sure proof that the fermentation of the must has been 

 properly conducted. 



Meanwhile only a part of the sugar has been decomposed, and 

 only a part of the yeast, or the glutinous substances which may 

 form yeast, even if these have been separated from the portions 

 which have been precipitated, or which still swim on the surface. 

 The fermentation, therefore, still continues ; the yeast and gum 

 yet present, combining with the air, go on converting the remain- 

 ing sugar into alcohol and carbonic acid until all the sugar is 

 consumed. 



This fermentation is called the After Fermentation. It goes on 

 very slowly, frequently requiring years to complete it if the wine 

 is kept in close vessels in a cool place. It may be known by the 

 wine becoming richer in alcohol, less sweet, and specifically light- 

 er. If this fermentation is comparatively vigorous, and the cask 

 is air-tight, the wine wnll effervesce when the cask is opened, or 

 may even burst the vessel if a great amount of carbonic acid has 

 been generated. 



If favored by a high temperature, or if the liquid contains a 

 large amount of undecomposed sugar or yeast, this after ferment- 

 ation may present more or less of the characteristics of the first 

 fermentation. This is generally prevented by clearing it off, cool- 

 ing, sulphurization, etc. 



If the yeasty parts remain in the liquid, the fermentation shows 

 itself in a different way. The yeast, settling down to the bot- 

 tom, decomposes the saccharine parts near it, together with the 

 alcohol. Air-bubbles then rise, indicating the commencement of 



