Two varieties of Californian wine, examined by J. L. de Fremery,[89] had the following composition:—

Grammes in 100 c.c.Gutedel (White).Zinfandel (Red).
Alcohol10·459·80
Extract2·09082·1270
Mineral matter0·19780·2218
Volatile acids (as acetic)0·08040·0972
Fixed acids (as tartaric)0·48450·4110
Potassium bitartrate0·15790·1428
Free tartaric acid0·0060..
Other free acids (as tartaric)0·58500·5325
Sulphuric acid0·03840·0168
Phosphoric acid0·02200·0193
Chlorine0·00360·0054
Lime0·00560·0084
Magnesia0·01700·0160
Glycerine0·61330·5647
Sugar0·01650·0276
Polarisation+0·2..
Succinic acid0·00680·0097
Malic acid0·03240·0922

According to analyses made by R. Fresenius and R. Borgmann,[90] natural wine has the following average composition:—

Grammes in 100 c.c.
Alcohol7·71
Extract2·75
Free acids0·73
Mineral matter0·23
Glycerine0·79
Sulphuric acid0·038
Phosphoric acid0·040
Lime0·018
Magnesia0·018
Potassa0·092
Chlorine0·004
Potassium bitartrate0·200

Natural wines are frequently subjected to various processes of treatment, designed to remedy certain defects existing in the original must. While these do not, perhaps, all properly come under the head of adulteration, it is certain that many of the practices resorted to affect the dietetic quality of the wine in a deleterious manner. The most common modes of treatment, generally considered harmless, are the following:—

Pasteuring, which consists essentially in heating the wine to 60°, with a limited supply of air, and effects the artificial ageing and better conservation of the product. Wines which exhibit ropiness and other diseases are restored by destroying the fungi present. This is accomplished by subjecting the well-filled and corked bottles to a temperature of from 45° to 100° for several hours.

A process of freezing is likewise employed for the improvement of wine. It results in the removal of much of the cream of tartar, colouring matter, and nitrogenous substances contained, and also causes an increase in the alcoholic strength of the wine, thereby considerably decreasing its tendency to undergo an after-fermentation.

The proportions of sugar and acid best adapted to the production of wine of good quality are at least 20 per cent. of the former to not more than 0·5 per cent. of the latter. As these conditions do not always obtain in grape-juice, artificial methods are employed to supply the necessary constituents. Of these, the most rational consists in diluting the must until the amount of acid is reduced to 0·5 per cent., and increasing the sugar to a proportion of 20 per cent. by the addition of glucose. In a somewhat similar process, due to Petiot, the marc is repeatedly mixed with water containing 20 per cent. of sugar, and then subjected to fermentation. In other methods, the removal of the excess of free acid is effected by neutralisation with pulverised marble or neutral potassium tartrate. The use of these agents results in the formation and subsequent separation of insoluble salts—in the latter case, of potassium bitartrate. Another process for the improvement and preservation of natural wine, proposed by Scheele, consists in the addition of glycerine, in a maximum proportion of 3 per cent., after the first fermentation has taken place.

R. Kayser[91] has made a very exhaustive investigation of wine-must of different sources, and of the wine prepared therefrom, both in its natural state and after having been subjected to various “processes of improvement.” The following table shows the results obtained from the analysis of Franken must and wine (both natural and “improved”), made from Riessling grapes in 1880:—