In submitting matured wines to chemical analysis it is found that they differ mate rially from one another in their composition; and especially as the wine is, or is not, red. In white wine no special coloring matters are found, and only a trace of tannic acid; while in red wine both are present. In wine generally the principal ingredients are alcohol and water; then sugar, gum, extractive and albuminous matters; then free organic acids, such as tartaric, racemic, malic, and acetic acid; and salts, such as the tartrates of potash, of lime, and of magnesia, sulphate of potash, chloride of sodium, and traces of phosphate of lime; also, especially in old wines, substances imparting aroma, as cenanthic and acetic ethers, and other volatile odoriferous matters (among which Mulder mentions butyric and caprylic ethers, each having a pineapple odor, eaproic, pelargonic, capric, and propionic ethers, amylic alcohol, and many of its ethers and other compounds, aldehyde, acetal, and probably racemic, citric, and malic ethers). In red wines, and in many others, a little iron, and possibly some alumina, may be found; and lastly, the best wines contain, according to Faure, a peculiar mat ter, which he terms cenanthin, and to which he ascribes the substance or body of the wine; but which seems to other chemists scarcely to differ from gum or dextrine. These ingredients, as Mulder observes, vary exceedingly in proportion. The quantity of some is so small that the substance almost disappears during analysis; others can just be determined by a delicate balance; while others, again, are freely present. Put ting aside taste and smell as standards of comparison, most of the essential dietetic and therapeutic properties of wine depend upon the alcohol, sugar, and free acids, especially tartaric acid, contained in it. In his chapter on "The Amount of Alcohol in Wine," Mulder gives a large number of analyses of different wines in which the percentage of alcohol is determined. We shall here only give the abstract of the analyses made by his translator. Dr. Bence Jones, who found that the alcohol varies in Sugar is found in all wines,* although in certain kinds very little exists. Accord ing to Fresenius the sugar in four kinds of Rhine wine amounts to exactly six-sevenths of the extract remaining after evaporation, the seventh part consisting of the salts and non-volatile unfermentable matter. In red Bordeaux. on the other hand, very little sugar is found; red sauterne contains less than 1 per cent of extract, and hermitage 1.7; hence the quantity of sugar must be very minute; while some kinds of muscat yield 24.5 of an extract, containing about 22 per cent of sugar. Small as is the quantity of sugar in some wines, it is of great importance in diminishing the sharp taste of the free acids, and in imparting an agreeable flavor to the wine. Good red wines should con tain at least one-half per cent of sugar, and the quantity is sometimes larger. Some of the sweet wines contain nearly one-fourth of their weight of saccharine matter.
The following results were yielded by the experiments of Dr. Bence Jones: Under the term " free acids" arc included the acid tartrate of potash, known as cream of tartar, and other soluble bitartrates found in wine, besides such acids as are quite uncombined, such as tartaric, inalic, and acetic acid, and a trace of free tannic acid. Sugar has so much power in concealing the free acids, that their amount cannot be estimated with any certainty by the flavour of the wine, and must be estimated chemically by ascertaining how much of an alkaline solution of given strength must be used in order to render a given quantity of wine perfectly neutral to test-paper. Vola
tile acids, as, for example, acetic acid, may either be determined separately, or included with the others ; and, excepting this acid, all the other acids occurring in wine may practically be calculated as tartaric acid. Mulder found that acetic acid was present in 20 different kinds of wine which lie examined, the amount of the anhydrous acid rang ing from 1.75 thousandth parts in Madeira to 0.25 thousandth parts in Tavella. In the same 20 kinds of wines, the free tartaric acid ranged from 2 to 7 parts in 1000 of wine, Tavella having the largest, and Bordeaux sauterne the smallest quantity. With regard to the tannic acid, traces of it may be found in all white wines, but in no white wine is it sufficiently abundant to be of the slightest importance in a medical or dietetic point of view. On the other hand, it is abundant in Port and heavily loaded Bordeaux wines, especially when new. In the course of time, this tannic acid becomes oxidized into a sparingly soluble compound, which is called by Berzelius the apotleema, or precipitate of tannic acid—a process which is facilitated by the exposure of the wino in bottles to full daylight. There is no doubt, that this acid, by combining with the albuminous matters, tends to increase the durability of these wines. .Dr. Bence Jones, in his Appendix to 3Itilder's treatise, gives numerous results of experiments made regarding the acidity of wines by Front, Liebig, Fresenius, and himself. His general conclusions are that, "proceeding from the least acid wine to the most acid, we have sherry, port, champagne, claret, Madeira, Burgundy, Rhine wine, Moselle. The ]east acid fluids examined were Geneva and whisky ; then rum, brandy, ale, porter, stout. The wines were all more acid than the malt liquids." Mr. Griffin has made 22 determinations of the acidity of light wines for Dr. Devitt, which arc published at the end of that phy sician's instructive little work on Cheap }Vines, and has subsequently published an independent volume on the mode of determining the acidity of wines.
In conclusion, we may say a word or two on " the diseases of wine," by which term we understand those conditions in which the wine has become so altered and unfitted for use as to have lost its distinct character. The most important of these diseases are: • 1. The turning of wine.—This disease is incidental to young wine, and seems to occur under special conditions of the weather. The color becomes darker, and the taste first disappears, and, if the disease goes on, becomes disagreeable; the wine becomes turbid and acid. This disease is caused by a decomposition of tartar.
2. The ropiness of wine.—This disease consists in the formation of vegetable mucus from the sugar of the wine, and is known as mucous fermentation. The wines liable to this change are those which are deficient in tannic acid.
3. The bitterness of wine—to which Burgundy wines are especially exposed—seems due to a second fermentation, inasmuch as a large amount of carbonic acid is evolved. It has been ascribed, whether correctly or not we cannot say, to the formation of citric ether, which is very bitter. The disease is caused by the sediment, and often ceases on being drawn off into other casks.
4. The acidifying of the wine depends upon the conversion of the alcohol into acetic acid, and may be stopped at its commencement by adding alkaline carbonates, which, however, destroy the colour, and affect the taste of the wine.