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.
In making red wine dark grapes are used, and both skins and stones are left to ferment with the pulp, to which they furnish tannin, pigment, and extractives.
Red wines, on the average, contain from 8.5 to 11 per cent of alcohol, 0.55 to 0.65 per cent of acid, and 0.15 to 0.20 per cent of tannin and pigment. The red wines are, as a rule, more easily digested than white, and are more nutritive.
The following practical statements are quoted from Leoser:
"Bottled red wines that are rich in tannic acid, like port, for instance, deposit a sediment and grow lighter in colour. Those that contain less tannic acid generally grow darker. The cause of this is a gradual diminution in the quantity of free acid in the wine. The effect of this acid is to turn the colouring matter red, and as it diminishes, therefore, the wine grows darker or more purple".
Red wine (claret) is often drunk diluted with Vichy, when "the potassium carbonate of the water saturates the free acid of the wine, and so destroys the red colour and permits it to become darker, while the action of the alkali upon the colouring matter gives it a cloudy appearance".
The deeper the colour the rougher is the flavour of the wine in most cases.
"If two wines of equal alcoholic strength be taken it will be found that equal doses of each will produce their effect much more quickly in the case of the white wine than in that of the red. The reason of this is that the astringent action of the tannic acid retards the effect of the alcohol upon the organism. It may be that this indicates in a general way the superiority of white wines as stimulants and red wines as tonics".
Various substances are used for "fining " - that is, to clarify wine - such as cream, milk, blood, solutions of egg albumin, gelatin, isinglass, nutgalls, lime, etc. Their effect is largely mechanical, but the alkalies neutralise part of the acids.
Other substances are occasionally employed, having in view the better preservation of wine, but many of these are unhealthful in their effects on the system. Such, for example, is the use of calcium sulphate, which is converted into potassium sulphate, or the use of alum, sulphuric or other acids, etc. Impure alcohol holding fusel 18 oil is sometimes added. The object of storing wine in enormous tuns is to diminish the surface exposed to the air in comparison with the bulk.