The grapes are collected and the juice pressed out either by treading or by more or less developed mechanical contrivances.
The juice or 'must' ferments which is to say that the sugar in the grape juice, is converted into alcohol. The chemistry of fermentation the action of yeast is a complex matter.
It is sufficient here to say that it is a bacteriological
process in which living micro-organisms increase and multiply, needing the active cooperation of oxygen from the air.
The primary fermentation therefore takes place with free
access to the air. The young wine is run off into casks or vats which are covered from the air for the secondary fermentation, in which the wine, at this stage a turbid liquid, clears by
throwing a deposit.
After a few months the bright wine is racked that is, separated from the deposit into a clean, sulphured cask. Not yet clear enough, it is 'fined' by the addition of white of egg or gelatine which, combining with the tannin in the wine, makes a further deposit and also carries down suspended particles.
Variations of the essential process are employed, according to the character of the wine to be produced. In from two to four years the wine is mature and ready for bottling, as in the case of
the Burgundies, Clarets, Champagnes, Hocks, etc., or for further maturing in the wood as in Port and Sherry.
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