WHAT IS WINE ? 
361 
position, and may accordingly he separated from the wine by 
distillation or evaporation; and, secondly, such as cannot be 
distilled without decomposition. The first consist chiefly of 
members of the fatty acid series ; acetic acid forming by far the 
greatest proportion. These are generally termed volatile acids ; 
the second, as tartaric and malic acid, are comprised among the 
fixed acids. If these acids form compound ethers, the ethers of 
the volatile acids are likewise volatile, and may with care be 
distilled off from the wine without suffering decomposition: 
the ethers of the fixed acids cannot be distilled without decom- 
position, and remain behind in the residue from which the 
volatile ethers have been driven off. 
Both classes of ethers admit thus of separate estimation ; in 
both cases, however, the aggregate amount only, and not the 
individual members that make it up, is estimated. None of 
the ethers of the fixed acids possess striking flavour, nor con- 
tribute much to the general character of the wine, beyond, 
perhaps, the neutralisation of part of the free acid effected in 
their formation. As the wine gets older, however, the amount 
of non-volatile ethers diminishes, the alcohol they contain being 
gradually transferred to volatile acids ; and in this manner these 
fixed acids facilitate the formation of the volatile ethers. Most 
of the volatile ethers, on the other hand, are distinguished 
by a very powerful and often, particularly when very diluted, 
extremely agreeable smell ; and a great part of the odour and 
bouquet of the wine is no doubt due to them. 
At the end of from five to twelve years, the wine may be con- 
sidered to have arrived at maturity; that is to say, the slow 
chemical changes going on have reached the maxinium amount 
that is still beneficial : after this the wine no longer improves 
by keeping, except to. the taste of a few would-be connoisseurs.* 
Generally speaking, the lighter classes of wine arrive sooner at 
maturity than stronger and heavier wines. The foregoing 
sketch refers chiefly to pure natural wines ; in strongly fortified 
wines, all chemical changes are more or less modified, and 
usually take a longer time for their consummation. Such wines 
require fifteen or more years to bring them to perfection ; such 
time being, in great measure, necessary to undo and correct the 
evil done in brandying them originally. 
The chemical changes taking place in the wine go on, how- 
ever, unceasingly in cask or even in bottle, owing chiefly to the 
oxygen finding its way by endosmosis through the sides of the 
cask, or even through the cork of the bottle ; or through its 
having been absorbed by the wine in the act of transferring it 
* Some, exceptionally rich, natural wines do improve even after twelve 
years, but the above statement will be found to be true in most cases. 
VOL. VII. — NO. XXIX. C C 
