Must contains

Wine contains

ferment oils

albumenoid substances

vegetable mucus

colouring matter

tannin

fatty oil

essential oils

extractives

mineral substances 0-15 to 0.6

Most of the above given substances are contained in every wine, although in very variable proportion, while some of them are found only in certain kinds; such, for example, as colouring matter, tannin, racemic acid, formic acid, aldehyd, &c. &c.

The character of a wine will, of course, depend upon the relative proportions of all the various constituents present, and a glance at the long list of substances found will suffice to show, that their intermixture in various proportion may readily give rise to an almost infinite variety. Some of these substances admit of accurate quantitative estimation, and their relation to certain characters of the wine it is thus, to a great extent, within the power of chemical analysis to determine. Many of them, however, do not as yet admit of being thus estimated; and, even if we are content with simply showing their presence, it is frequently necessary to operate on large quantities of the wine. Those constituents of a wine (as the alcohol, sugar, acids, mineral constituents, &c.) on which its physiological action chiefly depends admit of accurate estimation. Chemical analysis will, therefore, give us valuable information regarding its dietetic and medicinal qualities, and will show us its strength, as well as whether it is pure and sound, or the reverse, and whether genuine or factitious. On the other hand, most of the constituents upon which the quality of the wine-i.e. taste, and therefore market value-depends, are among those not admitting of accurate estimation. Chemical analysis alone, therefore, will afford, generally speaking, little or no information to guide us in this respect.

In entering upon a closer examination of their various constituents, it will be well to bear in mind the distinction, previously given, between the natural wine on the one hand and fortified or brandied wine on the other.

Pure, natural wine, is the fermented juice of the grape, without any addition or subtraction. Such a wine, when made of good ripe grapes and in favourable seasons, will exhibit all the vinous qualities in the highest perfection, and with the most complete concentration of the various constituents of the must. Not having been diluted by addition, or suffered loss by

removal, such changes only occur in it as are brought about by fermentation itself; such as, for example, the conversion of the sugar into alcohol, &c., the solution of colouring matter, precipitation of tartar, &c. &c. The wine, moreover, having once thoroughly fermented, is not very liable to further change in that direction, and is therefore wholesome and of excellent keeping quality. In fortified wine, on the other hand, fermentation has not been allowed to run its regular course, but has been checked prematurely by the addition of spirit, by which the strength of the wine is brought above the limit within which, as we have learned, vinous fermentation is possible. The wine, therefore, although of good keeping quality as long as its strength is unimpaired, is liable to ferment whenever the preserving power of the spirit added may be destroyed by dilution, as, for example, when the wine is drunk. It is on this account less wholesome than the pure wine. The concentration of the wine also is lessened by the addition of the spirit, in consequence of which it contains relatively less constituents of the grape than the natural wine. The fortified wine certainly often contains no inconsiderable amount of sugar which has been preserved from fermentation, and this induces the belief that greater concentration exists; but this sugar has only been preserved at the cost of a great addition of spirit, whereby all the other constituents have been diluted.† This sugar, moreover, if required, could be obtained much more cheaply as cane sugar. A bottle of port wine with 4% of sugar (and this is a sweet port) contains about 13 of sugar, of the value of one-third of a penny.

• Medical men will probably find in this an explanation of the fact that even good fortified wines are liable to produce flatulency and dyspepsia in persons with weak digestion. The wine is drunk, either already diluted with water, or is subsequently diluted by the gastric juice; the protecting power of the spirit is destroyed, and fermentation and consequent acidity are the necessary result.

† An example will, perhaps, make the case more clear. Supposing a must from which port is to be made to contain 28°。 of sugar-and this would be a very good must-it would be capable of producing a wine having a strength of about 13%. If now 4° of sugar are to be retained in the fortified wine, the strength produced by fermentation will barely reach 10%, and, as the wine has to be brought up to say 19°。 (42 degrees proof spirit), about 30 bottles of proof spirit have to be added to every 100 bottles of wine. All the vinous qualities before contained in 100 bottles are now distributed through 130 bottles, or one bottle of the fortified wine contains only about three-fourths of a bottle of real wine. The dilution will be somewhat less if stronger spirit is employed, but the general fact will remain the same. If, as is frequently the case, grain spirit or even potato spirit is used for admixture, dilution is not the only drawback, inasmuch as substances quite foreign to the genuine wine are, in that case, introduced in addition.

Let us now turn to the consideration of the chief constituents of the wine, more particularly of such as admit of quantitative estimation. The most important of these is

Alcohol.-Ethylic alcohol, or spirit of wine. As before explained, the sugar of the must breaks up, in the course of fermentation, chiefly into carbonic acid and alcohol, the former escaping into the air, the latter remaining in the wine.

By submitting the wine to distillation, this alcohol can be separated from the rest of the constituents and estimated.

Generally speaking, all wines which are simply the fermented juice of the grape (natural wines) contain from 60 to 130 parts by weight of alcohol in 1,000 volumes of wine (6 to 13%). With less than 60 parts the wine is scarcely drinkable, and more than 130 parts cannot, except in a very few rare cases, be contained in a natural wine. Firstly, because grape juice seldom contains the requisite amount of sugar for the production of more alcohol than this; and, secondly, because such an amount represses, or altogether stops, fermentation, and so protects the rest of the sugar from decomposition. A wine of more than 13% of alcohol is almost certainly a fortified wine; the great majority of natural wines contain less than 12%.

In fortified or brandied wines the strength, of course, depends on the amount of spirit added, and on the original strength of the wine; it may, however, be taken as ranging between 120 and 220 parts per 1,000 volumes (12 to 22%), being rarely above and rarely below that amount.

Besides this ethylic alcohol wine contains, as we have seen, small proportions of a number of other alcohols; as, for example, propylic, butylic, amylic alcohol, &c. &c. These alcohols are closely allied, chemically, to ethylic alcohol; indeed, they are termed alcohol on that account, and are, like it, produced during the fermentation of sugar. They have, undoubtedly, a great influence upon the bouquet of the wine, and perhaps also upon its physiological action. At present they do not admit of accurate quantitative estimation.

Acids of Wine.-All wine contains a greater or less proportion of free acid, and possesses, therefore, an acid reaction and a sour taste; but whilst the degree of acidity, as measured chemically, depends only upon the proportion of acid present, the acidity, as judged by the palate-the more or less sour taste of the wine-is greatly influenced by the nature of the acid and the presence or absence of other constituents. Thus a wine of low alcoholic strength, and without sugar, will taste unpleasantly sour, with a degree of acidity which, in a strong and sweet

wine, would scarcely be perceived, the sugar and spirit in the latter case masking the sour taste. This effect should never be lost sight of in judging of the relative acidity of natural and fortified wines. Good wines of either sort contain in reality pretty nearly the same amount of acid, but in the fortified wine the sour taste is, as above described, less prominent. It is, however, a great mistake to suppose that, because the acid is masked to the taste, that it is not present; and any injurious effects that may be supposed to follow its use in the one case will most assuredly also follow in the other.

The acids of wine may be conveniently divided into two classes: firstly, non-volatile or fixed acids, such as cannot be distilled over or expelled by evaporation without decomposition; and, secondly, volatile acids, which can be distilled or expelled.

The acids of the first class are all derived directly from the grape juice, but are present in the wine in a different proportion to that in which they were contained in the must; for the salts of some of these acids (those of tartaric acid, for example) are less soluble in the wine than in the must, and are consequently precipitated during fermentation. The chief acids of this class are malic acid and tartaric acid, the former usually predominating. In pure natural wines, made of ripe grapes, tartaric acid is probably never absent; but its amount varies considerably, though rarely or never equalling the amount of malic acid present. In some wines part of the tartaric acid is replaced by the closely allied racemic acid. Generally all the tartaric acid contained in a wine is present in the form of an acid potassium salt (cream of tartar); only one half of it contributes, therefore, to the acidity of the wine, one half being neutralised by the potassa.

In all fortified wines, plastered wines, or wines otherwise subjected to artificial treatment lessening the acidity, there is considerably less tartaric acid; indeed, in such wines it is frequently totally absent.

The volatile acids have all been formed during or after fermentation; they are produced by the action of oxygen on some of the constituents of the wine, representing, so to speak, the first beginnings of its ultimate destruction. In small quantity they are indispensable to the wine, being chiefly instrumental in the production of its flavour and bouquet. When present, however, in large quantity, they are very objectionable, affording undoubted evidence of maltreatment of the wine, and rendering it very liable to turn sour altogether, i.e. to become vinegar. Such wines, therefore, should be carefully avoided. Among the volatile acids present the acetic is found in greatest proportion, and is formed by the oxidation of the ethylic alcohol. Besides this acetic acid there are always small quantities

of other homologous acids, such as propionic acid, butyric acid, &c. &c. It is to these latter that the production of the bouquet is chiefly due.

In good sound wines the total amount of free acid, that is, acid not combined with or neutralised by an alkali, varies from three to six parts per thousand, calculated as if all the acid were tartaric acid. This, as before stated, is not strictly correct, but it is the conventional method of expressing the acidity of a wine. In the case of white wines, not fortified, not more than about onefourth of the total acidity should be due to volatile acids; in the case of red wines, or fortified wines, the proportion of volatile acid is generally higher, but should not, even in these, amount to more than about one-third of the total free acid.

Sugar in Wine.-Grape juice contains two kinds of sugar in equal proportion-grape sugar and fruit sugar. Both these sugars are capable of fermentation, both are destroyed by being heated with a solution of an alkali, and both reduce copper salts from their warm alkaline solutions. The first, however, is crystallisable, and turns the plane of polarised light to the right; the second forms an uncrystallisable syrup, and turns the plane of the polarised ray to the left about twice as much as the other turns it to the right. A mixture of both in equal proportion, such as is found in the grape, will therefore turn the ray about half as much to the left as pure grape sugar turns it to the right. This same mixture of sugars is produced by the action of yeast, or acids, on cane sugar, and is then called invert sugar, since, as above explained, it turns the plane of polarised light to the left, cane sugar turning it to the right. Cane sugar then, when added to must, or wine, very soon becomes changed into invert sugar--a mixture of sugars identical with that found in the grape-and a few weeks after its addition is no longer found as cane sugar. During the fermentation of the must grape sugar chiefly is destroyed, so that the sugar remaining in the wine is in greater part fruit sugar.

By the action of sulphuric acid on starch, a sugar is produced chemically identical with grape sugar (not with the mixture of sugars as found in the grape), and this is frequently employed in the adulteration of must and wine.

Natural wines, when more than a few years old, contain, as a rule, little or no sugar. Young wines of this class not unfrequently, however, retain an appreciable quantity of sugar, amounting in some rare instances even to 6%, though more usually to 0.5 or 2% only. As long as the wine contains this amount of sugar, it is very apt to enter again into fermentation, and must therefore be kept for some years in cask, and in a cool cellar, before it can be safely bottled. In time this sugar gradually diminishes, even without any decided fermentation,