But to return to our subject.  As soon as the stormy or seething fermentation is over, the young wine is drawn off from the fermenting-vat into the maturing-cask, at which time it may be quite warm and turbid.  In a cool cellar and with perfect quiet it gradually becomes clearer; it deposits on the bottom of the cask many of the substances it contains, and the fermentation becomes no longer visible.  The time which this “slow fermentation” takes to occur will vary with the type of wine, with the nature of the must, and with the influence of the season.  Speaking generally, it may be said to be from two to eight weeks after its entrance into the maturing-cask.  The wine is considered to be ready for its first racking when it has become clear and transparent, and when its lees have subsided to the bottom of the cask.

In racking there is a withdrawal of the wine from the sediment which it casts down, and which is known as the lees.  It is an important operation because irremediable damage is caused to wine by allowing it to remain in contact with the dregs.  A knowledge of their composition is of great value, since it serves to explain their injurious influence.  The lees deposited from vinous fermentation consist of mineral salts, tartaric acid, and organic matters.  Of these the ’organic substances are the most to be dreaded, and for this reason, that they are very prone to rapid decomposition.  They consist of yeast-cells, cells of other micro-organisms, of debris and minute particles of grape stalks and skins, and of other bodies, all readily liable to decompose.  All these various materials, therefore, are continually a source of peril, for the slightest thing may start action in them, which spreads throughout the wine and simply ruins it.  By removing it from such undesirable company all these risks are avoided, and the best possible qualities of the wine are afforded the opportunity to develop.  In the performance of racking definite changes take place in the vine, which are assuredly important.  For it must be remembered that the nearly fermented young wines contain an excess of carbonic acid gas; and this is rightly regarded as possessing great preservative properties, in that it prevents the dangerously spreading growth of the little micro-organisms and germs present in all new wine.

In the course of racking, however, a certain amount of the carbonic acid gas must be lost, and fresh oxygen is absorbed from the atmosphere.  The oxygen is invaluable from the fact that it exerts a powerful chemical influence upon the wine; as a consequence fermentation is slightly renewed if there be any grape sugar remaining.  At the same time the colour of the wine is also modified, and any rawness or harshness in its taste quality is enormously increased by the development of those delicate and subtle ethers which have so much to do with the flavour and bouquet of all wines.