This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
White wine is made from grapes of any colour, the greatest care being taken not to macerate the berries in expressing the juice, and to allow no coloured juice to flow. As a rule, however, the better class of white wines is made from selected white grapes, which are crushed with their skins. The mass is left for several days, so that the skins may impart what little soluble matter they contain to the pulp. The juice is then obtained by further pressure and allowed to ferment. The crushing of grapes was formerly done by the feet of men who trampled upon them, but several lives were lost by carbonic-acid gas poisoning, and the process is now generally conducted by machinery.
After several months, or longer, the ferment and the salts which are insoluble settle in a sediment called lees, and the supernatant fluid is carefully drawn off and casked or bottled.
During the first year or so of storage some wines are recasked several times, for they continue to deposit lees on the bottom and sides of the cask, consisting mainly of "argol," an acid salt from which cream of tartar may be prepared.
When fermentation has proceeded long enough it is stopped, according to the nature of the wine, by the addition of alcohol or strong sugar solution, or if left to continue after the wine is stored, the sugar and extractives very gradually disappear, and alcohol continues to develop.
Hence, if a wine can be bottled early without being too green or immature it is sometimes a decided advantage, for more of the aroma and flavour may be thus retained.
In other cases wines should remain in the casks for from one to four years before bottling - the more delicate varieties being kept the longest - for certain changes depend upon the size and nature of the containing receptacle, which are checked by bottling. Pavy says: "By keeping in a cask, wine increases in alcoholic strength. This is to be accounted for by wood being more easily penetrated by water than by alcohol. Thus it happens that water is lost by evaporation from the outside of the cask in larger quantity than the alcohol, and the wine is left in a more concentrated condition".
White wines are produced in more variety than red wines. On the average they contain from 9 to 12 per cent of alcohol, from 0.30 to 0.50 per cent of sugar, and about 0.50 per cent of acid.