WHAT IS WINE? 
357 
air has access to it, and various processes of oxydation are set 
up. Some of the alcohol formed becomes oxydised into acetic 
acid ; and most probably part of the albuminous and fatty sub- 
stances of the must are converted into acids, homologous with 
acetic acid, as propionic, butyric, propylic, pelargonic, &c., 
belonging to the series of so-called fatty acids. At the same 
time a variety of essential oils, termed ferment oils, are fre- 
quently produced, to which the perfect wine often owes part of 
its aroma. 
As soon as a moderate quantity of alcohol has been formed in 
the must, it effects great changes in the solubility of various 
constituents. Thus, bitartarate of potassium, being less soluble 
in alcoholic liquids than in water, begins to be deposited ; and 
this precipitation keeping pace with the increasing amount of 
alcohol, the must becomes thereby less and less acid. On the 
other hand, the colouring matter of the skins, being soluble in 
spirit in the presence of acid, is gradually dissolved in proportion 
to the increasing amount of alcohol. 
The progress of this first fermentation will, however, be greatly 
influenced by the temperature at which it takes place. If the 
temperature is low, fermentation proceeds slowly, and is accom- 
panied by fewer products of oxydation ; if, on the other hand, 
the temperature is high, fermentation goes on rapidly, and 
oxydation is at the same time augmented. Lastly, the quantity 
of sugar, as well as the amount of alcohol produced, exercises a 
considerable influence on the must, A must which contains 
more than 25 or 28 per cent, of sugar does not ferment so 
readily as when it contains less ; while, if more than 1 2 per cent, 
of alcohol have been produced, fermentation is also to a con- 
siderable extent impeded. At low temperatures, indeed, it does 
not proceed at all ; at a moderate temperature it proceeds but 
slowly, in which state of things great danger of excessive oxyda- 
tion is incurred. On the Ehine and in most parts of France, the 
temperature during the time of vintage is not generally very 
high, and is frequently but little above the lower limit at which 
vinous fermentation is possible, viz. 7° C. The must, also, in 
these countries rarely contains more than 25 per cent, of sugar. 
Their wines, therefore, may be allowed to ferment thoroughly 
without fear of excessive oxydation ; whence they retain little or 
no sugar, and are almost free from albuminous substances. In 
Spain, Portugal, and other southern countries, however, the tempe- 
rature during the vintage is high, sometimes almost reaching the 
higher limit, viz. 36° C., at which vinous fermentation is possible, 
and being within that which is favourable to acetous fermenta- 
tion ; the must also frequently contains more than 25 per cent, 
of sugar. In these countries, then, it is often impossible to allow 
fermentation to proceed to its full extent ; and it is frequently 
