Wine is the fermented juice of the grape of Vitis vinifera. In its preparation, the fully matured grapes are usually (but not always) first separated from the stalks, and then crushed, the marc so obtained being afterwards placed in butts provided with perforated sides, through which the expressed juice or must percolates. It is next introduced into vats, and allowed to undergo a process of fermentation, which is very analogous to that of beer wort. The addition of yeast is, however, in this case unnecessary, as the fermentation of grape-juice is spontaneous, it being due to the generation of the fungus Penicillium glaucum, which is the product of the action of atmospheric germs upon the albuminoid matters contained in the must. The most important constituents of grape-juice are glucose (10 to 30 per cent.), organic acids (0·3 to 1·5 per cent.), and albuminous substances. During the fermentation the glucose is converted into alcohol and carbonic acid, the latter being evolved in bubbles; a deposit of potassium bitartrate and yeast-cells, forming the lees, likewise occurring. This first fermentation ceases after the lapse of several days, the period being indicated by the cessation of escaping gas. In order to prevent the oxidation of the alcohol to acetic acid, the liquid is removed from the lees and transferred into casks, in which a slow after-fermentation and a further separation of potassium bitartrate take place. The wine is subsequently stored for a considerable time in fresh casks, during which it “ages,” and acquires its characteristic flavour.

The more common varieties of wine are classified according to the country of their production—into French (claret, burgundy, champagne, etc.), German (Rhine), Spanish (sherry and port), and Italian.

The production of American wine has experienced a noteworthy increase during the past twenty-five years. While, in 1860, less than two millions of gallons of native wine were consumed in the United States, in the year 1884 the quantity used exceeded seventeen millions of gallons.[87] Aside from the general distinction of red and white, wines are classified by their characteristic properties, as dry, sweet, and cordial. In dry wines, such as those of the Gironde and Rhenish districts, considerable free acid, and but little or no sugar are contained, whereas in sweet wines (Madeira, port, etc.) a certain proportion of the sugar remains undecomposed. Cordial wines are distinguished by their sweetness and comparatively heavy body. The nature of wines is materially affected by the proportion of glucose and acids contained in the original must, as well as by the environments of their manufacture, such as climate and temperature. From a chemical point of view, the most important constituents of wine are the primary products of fermentation—alcohol, succinic acid, and glycerine, but its market value is far more dependent upon the flavour and bouquet, which are chiefly due to the formation of secondary products, usually included under the name “oenanthic ether,” and consisting of the ethers of caproic, caprylic, and other organic acids.

The following table exhibits the constituents of some of the best known varieties of wine, according to results obtained by different authorities:—

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

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

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:—

Magnier de la Source[92] has recently made some investigations concerning the difference in chemical composition of natural and plastered wine; he gives the following constituents of 1 litre of wine:—

Adulteration of Wine.—Although there may be some question in regard to the moral status of the foregoing methods of improvement of natural wine, numerous other practices are resorted to concerning which no doubt can exist. The more common forms of wine adulteration include plastering, sulphuring, fortification, blending, flavouring, colouring, and the manufacture of fictitious imitations.

The “plastering” of wines consists in the addition of plaster of Paris (often mixed with lime), either to the unpressed grapes or to the must. The process, which is rather hypothetically claimed to aid in the preservation of the wine and correct any excessive acidity, is very objectionable, in that it determines the formation of free sulphuric acid and acid sulphates, as well as of calcium tartrate and potassium sulphate. The lime salt, being insoluble, is deposited with the lees; the potassium sulphate, however, remains in solution, and as it exerts a decided purgative effect, its presence in wine cannot fail to be detrimental. In France, the sale of wine containing over 0·2 per cent. of potassium sulphate is prohibited. The plastering of wine is chiefly carried on in Spain, Portugal, and southern France. The ash of pure wine does not exceed 0·3 per cent., but in the samples of sherry usually met with it reaches a proportion of 0·5 per cent., and is almost entirely composed of sulphates. The “sulphuring” of wines is also extensively practised. It is effected either by burning sulphur in the casks or by conducting sulphurous acid through the wine itself, the object sought being to preserve the product and impart to it the ripeness naturally acquired by age. Sulphured wines, while not necessarily showing an increase in the amount of ash, can often be recognised by the abnormally large proportion of sulphates present.

The strength and preservative qualities of wine are frequently augmented by the addition to it of inferior sorts of brandy. Port wine usually receives an addition of about 30 per cent., and sherry is invariably fortified, if not to so great an extent. By the Customs regulations in England, 10 per cent. of brandy is allowed to be added to wines in bond, while, in France, the sophistication is equally permitted in wines intended for export, provided the total amount of alcohol in the fortified article does not exceed 21 per cent.

Doubtless the mixing or blending of wines constitutes the most frequent form of their sophistication. Natural wines of the same manufacture vary to some extent from year to year in colour, flavour, and other characteristic properties, and mixing is resorted to in order to supply the trade with a product always possessing nearly identical qualities. In many cases, the flavour of wines is improved by blending, and their intoxicating effects are also increased, both results being due to the formation of compound ethers. Common instances of wine mixing are the addition of Hermitage and Rousillon wines to clarets; of Malaga and Teneriffe to port; of solaras (a mixture of Amontillado and Manzanilla) to sherry; and of a liqueur composed of sugar, some kind of full, rich wine, and brandy, to champagne. The flavour and bouquet of expensive wines are frequently imparted to inferior grades by the addition of various substances, among which are elderflowers, orris root, cherry water, essential oil of almonds, sweet briar, and numerous perfumes, such as orange-flower water, neroli, essence de petit grain, violet petals, etc. The tincture of raisin seeds is said to communicate a genuine port flavour to poor wines, and a grain of ambergris, triturated with a little sugar, is stated to impart a much esteemed bouquet to a hogshead of claret. Numerous tinctures, as those of strawberry root, raspberries, and walnuts, are likewise used. Sweet and liqueur wines are extensively imitated at Cette and Montpelier. The following recipes[93] will serve to illustrate the general character of the mixtures employed:—

Port is frequently flavoured with a mixture of elderberry juice, grape juice, brown sugar, and crude brandy known as “Jerupiga.” Sherry often consists of Cape wine mixed with honey, bitter almonds, and brandy. Astringency is conveyed to wines, deficient in this quality, by means of tannin; and the property of forming a crust on the interior of the bottle is produced, especially in port, by the admixture of cream of tartar and gum. “Dryness” is also obtained by artificial methods. A preparation met with in the trade, and used for this purpose, has the following composition:[94]—

The colour of white wines is caused by the oxidation of the tannin present, but it is sometimes increased by the addition of the concentrated juice of highly-coloured grapes, or by means of a small proportion of caramel. The colour of natural red wine is due to the presence of oenocyanin, a bluish-black compound, chiefly contained in the grape skins, which is insoluble in water, but dissolves in acidulated alcohol. In Spain and southern France, a wine prepared from a vine known as the Teinturier, and possessing an intense bluish-red colour, is extensively employed for colouring of wines. There appears to be no doubt but that elderberries, black cherries, mulberries, and hollyhock are also frequently used as colouring agents. Souberian[95] mentions a mixture, termed liqueur de fismes, composed of elderberries, but also containing about 5 per cent. of alum, which is occasionally employed. The general use of several deleterious dyes, such as logwood, cochineal, and the aniline colours, is far more problematical. In regard to the last-mentioned agents, it has, however, been asserted,[96] that in a commune near Beziers, of 1800 inhabitants, magenta, to the value of 30,000 francs, is annually consumed in the adulteration of wine.

It is also worthy of remark that an aniline preparation used in Spain for the artificial colouring of wine has recently been found to contain 1·62 per cent. of arsenic acid.[97]

Owing to the ravages of the phylloxera, a very considerable decrease in the source of natural wines has taken place during the past few years. Between 1883 and 1884 no less than 22 thousand acres of vineyards were entirely destroyed in the Gironde district alone, and it is stated, upon good authority, that the total production of wines in France in 1884 was 220 millions of gallons less than the average of the previous ten years.[98] There is no doubt but that this decrease has greatly stimulated the manufacture of imitation wines. These occasionally contain a certain proportion of genuine wine as the basis, but more frequently they consist entirely of factitious constituents. The following recipe furnishes a fair example of those of the first class:—

Agitate thoroughly, add the white of two eggs, with constant stirring; allow to settle, and draw off.

Of late years, the production of wine from dried fruit has assumed very extensive proportions in France. The product, which is generally known as “vin de raisins secs,” is claimed by its manufacturers to be wholesome.[99] A wine said to possess the qualities of a fair claret, is made by submitting to fermentation the following mixture:—

Another recipe for Bordeaux wine is:—

It is authentically stated that in the year 1881, 52 millions of gallons of factitious claret wine were made in France, and the industry has certainly not diminished in extent since this date. It is a significant fact that the importation of Spanish raisins into France has undergone a remarkable increase during the past few years. Nor is this species of sophistication confined to foreign wines. Establishments are in active operation in New York City and elsewhere in this country, where imitations of Californian hock and claret are made from fermented infusions of dried fruit (often charged with salicylic acid), and offered for sale at less than thirty cents per gallon, with more than the usual trade discount.[100] According to a reliable estimation, less than one-tenth of the wine sold as champagne is actually the product of that district, the remainder being fabricated from other wines or from cider.

Analysis of Wine.—The analysis of wine comprises the following estimations:—Specific gravity, alcohol, extract, sugar, polarisation, glycerine, total free acids, volatile acids, free tartaric acid, potassium bitartrate, malic acid, succinic acid, tannin, ethers, ash, chlorine, sulphuric and phosphoric acids, and colouring matters.

Specific gravity.—The density is determined by means of the gravity bottle, at a temperature of 15°.

Alcohol.—The proportion of alcohol is ascertained by the distillation of 50 or 100 c.c. of the wine in a suitable flask, which is connected with a Liebig’s condenser, until about half of the liquid has passed over. The distillate is made up to the original volume with water, and its specific gravity taken, from which the amount of alcohol (by weight) present is calculated by aid of the usual alcohol-metric tables (see p. 196). The result (as well as the proportions of the other constituents) is preferably stated in grammes per 100 c.c. of wine. The determination may also be made by first removing the alcohol by evaporation, adding distilled water to restore the original volume, and then estimating the density of the liquid (see under Beer, p. 142). In unfortified wines the alcoholic strength ranges from 6 to 12 per cent., and in wines which have received an addition of spirit, it may vary from 12 to 22 per cent.

Extract.—The extract is conveniently determined by evaporating 50 c.c. (measured at 15°), in a platinum dish over the water-bath, the residue being dried for 2½ hours in the steam-oven. In case a wine rich in sugar (containing, say, over 0·5 grammes per 100 c.c.) is under examination, 20 c.c. will suffice for the determination. The indirect method used in the estimation of the malt extract in beer may also be employed. According to Girardin and Pressier, it is possible to detect the watering of certain wines, the average composition of which is known, by means of the proportions of extract and alcohol present. For example, in genuine Bordeaux wines the proportion of extract ranges from 20 to 20·8 grammes per 1000 c.c., and the amount of alcohol is also very constant, it being a mean of 100 grammes per 1000 c.c. Should a sample of Bordeaux wine show an extract of 14·5 grammes per litre, the proportion of genuine wine present would be 72·5 per cent., for 1000 × 14·5 20 = 725·00, the remainder being water and alcohol. In order to estimate the amount of spirits artificially added, the alcohol contained in 72·5 parts of the wine is determined. If, for instance, it is found to be 11 parts, then, (11 - 7·25 = ) 3·75 parts of alcohol have been added.[101] The quantity of extract in pure natural wine varies from 1·5 to 3 per cent., but in sweet and fortified wines, it may reach 10 per cent. or more.

Sugar.—The sugar in wine consists of a mixture of fruit and grape sugar, usually in the proportion of 3 parts of the former to 1 part of the latter. The amount of sugar is best estimated by Fehling’s solution (see p. 111). In the case of white wines, it is advisable to employ 100 c.c. for the determination; with sweet rich wines 25 c.c. are sufficient. The alcohol is first removed by evaporation over the water-bath, and the diluted liquid is next decolorised by means of bone-black or plumbic acetate, filtered, and made alkaline by addition of sodium carbonate. It is then made up to a volume of 200 c.c. and gradually added to 10 c.c. of Fehling’s solution. It is always well to test the wine by the polariscope, and, whenever the presence of cane sugar is indicated, to invert 100 c.c. of the sample by heating with a few drops of hydrochloric acid, and again make a sugar determination with Fehling’s reagent after neutralisation with sodium carbonate.

Polarisation.—The optical examination of wine is conducted by adding 20 c.c. of plumbic acetate solution to 100 c.c. of the sample, shaking the mixture, allowing it to stand for a short time, and passing it through a filter. If necessary the filtrate is further decolorised with animal charcoal and again filtered. The polariscope tube is then filled with the clear solution and the reading made. The majority of wines exhibit a left-handed polarisation, which is due to the fact that, as a rule, the proportion of fruit sugar present predominates over that of grape sugar; moreover, ½ part of fruit sugar will neutralise the dextro-rotary action of 1 part of grape sugar. In case the presence of an excess of grape sugar is indicated by the polariscopic examination, it is often assumed that this body has been directly added to the wine. It sometimes occurs, however, that, in the fermentation process, more grape sugar remains undecomposed than fruit sugar, under which circumstances the preponderance of the former body in the resulting wine would not prove sophistication; but, under ordinary conditions, the presence of an excessive proportion of grape sugar may safely be regarded as strongly pointing to the artificial addition of must syrup.

Glycerine.—100 c.c. of the wine are reduced by evaporation on the water-bath to 10 c.c., some pure sand added, and then milk of lime to decided alkaline reaction, after which the mixture is evaporated nearly to dryness. When cold, the residue is thoroughly agitated with 50 c.c. of 96 per cent. alcohol, next heated to boiling on the water-bath, and then passed through a filter. The insoluble residue is repeatedly washed with more hot alcohol, the washings being added to the first filtrate. The solution is now evaporated until it assumes a viscous consistency. The residue is taken up with 10 c.c. of absolute alcohol, and 15 c.c. of ether are added, the mixture being shaken and allowed to stand at rest in a well-stoppered flask until it becomes clear. The solution is subsequently filtered into a tared glass capsule, then carefully evaporated to a syrupy condition over the water-bath, and the residue dried in the steam-oven for one hour, and finally weighed. According to Pasteur, 112·8 parts of grape sugar yield 3·6 parts of glycerine; in natural wine, therefore, the glycerine should amount to about 1/14th part of the alcohol present.

Acids.—The acids in wine consist of acetic, tartaric, malic, tannic, succinic, racemic, formic, and propionic.

Total free Acids.—These are determined by titrating 10 c.c. of the sample with 1/10th normal soda solution, litmus paper or tincture of logwood being employed as the indicator. Wines containing free carbonic acid should be repeatedly well-shaken before making the estimation. The free acids are expressed in terms of tartaric acid (C4H6O6). If sulphuric acid or potassium bisulphate is present, a piece of filter paper will be rendered brittle when immersed in the wine for some time, and afterwards cautiously dried.

Volatile Acids.—The volatile acids are estimated by slowly evaporating 10 c.c. of the wine to the consistency of a syrup, and repeating the titration with 1/10th normal alkali solution. The difference in acidity represents the proportion of volatile acids present, which is stated in terms of acetic acid (C2H4O2). It is evident that the non-volatile acids can be calculated by deducting from the total amount of free acids, the tartaric acid corresponding to the acetic acid found. The proportion of volatile acid in genuine wine varies from 0·3 to 0·6 per cent. According to DuprÉ, in white wine, one-fourth of the total acidity should be due to volatile acids, and in fortified and red wine, they should not exceed a proportion of one-third.

Free Tartaric Acid and Potassium Bitartrate.—In the presence of a small amount of free acids, the detection of a considerable proportion of free tartaric acid may fairly be considered as strong evidence that the wine is artificial. Nessler recommends the following qualitative test:—20 c.c. of the sample are repeatedly shaken with a little freshly prepared and finely ground cream of tartar. After standing one hour, the solution is filtered, 3 or 4 drops of a 20 per cent. solution of potassium acetate are added, and the mixture is allowed to remain at rest for twelve hours, when, in presence of free tartaric acid, a precipitation will take place. The quantitative estimation of free tartaric acid and potassium bitartrate is made by Berthelot’s method, as follows:—Separate portions of the wine (20 c.c. each) are introduced into two flasks, a few drops of 20 per cent. solution of potassium acetate being added to the second flask. 200 c.c. of a mixture of equal parts of alcohol and ether are then added to both flasks, their contents repeatedly shaken and finally set aside for eighteen hours at a temperature between 0° and 10°. The separated precipitates are now removed by filtration, washed with the ether-alcohol mixture, and then titrated with 1/10th normal alkali solution. That formed in the first flask corresponds to the potassium bitartrate originally contained in the wine; the second represents the total tartaric acid present. The addition of a small quantity of clean sand will assist in the separation of the precipitates.

Malic Acid.—A slight excess of lime-water is added to 100 c.c. of the wine, and, after standing for some time the solution is filtered, concentrated by evaporation to one-half its original volume, and treated with an excess of absolute alcohol. The resulting precipitate (consisting of calcium malate and sulphate) is collected upon a filter, dried and then incinerated. The proportion of malic acid contained is now estimated by volumetrically determining the amount of calcium carbonate present by means of a normal acid solution: 1 part of calcium carbonate represents 1·34 parts of malic acid (C4H6O5).

Tannic Acid.—10 c.c. of the sample are taken, the free acids present neutralised with normal alkali solution, and a few drops of concentrated sodium acetate solution (40 per cent.) added. A solution of ferric chloride (10 per cent.) is then added, drop by drop, carefully avoiding an excess. A single drop of the iron solution represents 0·05 per cent. of tannic acid. The method of tannin determination described under Tea (see p. 22) can also be applied.

Succinic Acid.—500 c.c. of the wine are decolorised with bone-black, filtered, the filtrate evaporated over the water-bath nearly to dryness, and the residue repeatedly treated with alcohol-ether. The solution thus obtained is concentrated, carefully neutralised with lime-water, evaporated to dryness, and the glycerine present removed by washing with the alcohol-ether mixture. The remaining residue is now treated with 80 per cent. alcohol, in order to dissolve the calcium succinate contained, every 100 parts of which represent 75·64 parts of succinic acid (H6C4O4). Thudichum and DuprÉ state that one litre of pure wine contains from 1 to 1·5 grammes of succinic acid.

Ethers.—The compound ethers in wine are volatile and fixed, and exist in but minute proportions. Of the former class, ethylic acetate C2H3(C2H5)O2 is the most important. As already mentioned, the aroma of wine is largely influenced by the presence of the ethers of the fatty acids, butyric, caprylic, etc. DuprÉ determines the proportion of both kinds of ethers indirectly as follows:—250 c.c. of the wine are distilled until 200 c.c. have passed over. Water is then added to the distillate to a volume of 250 c.c. 100 c.c. are first titrated with 1/10th normal soda solution. Another 100 c.c. of the distillate are next heated with a known quantity of alkali (by which the ethers are decomposed into their corresponding acids and alcohol), and the titration is repeated. The amount of volatile ethers is then calculated from the increased acidity shown by the second titration. In order to determine the proportion of fixed ethers, 500 c.c. of the sample are evaporated over the water-bath to a small volume which is made alkaline, and then subjected to distillation. The distillate is acidulated with sulphuric acid and again distilled. The alcohol present in the second distillate is now oxidised to acetic acid by means of potassium dichromate, and the amount of this acid found estimated by titration. According to Berthelot, the proportion of ethers in genuine wine bears a fixed relation to the amounts of alcohol and acids present: he suggests the following formula for calculating the amount of alcohol contained in the compound ether of one litre of wine, when etherification is complete:—

y = 1·17 A + 2·8

x = y × a 100 ,

where A is the percentage, by weight, of alcohol; a the amount of alcohol equivalent to the total free acid in one litre of wine (assuming this to be acetic acid); y, the proportion per cent. of a present as compound ether in one litre of wine, when the alcoholic strength of the wine is A; and x, the amount of alcohol present in the compound ether of one litre of wine.

The Ash.—100 c.c. of the wine are evaporated to dryness in a platinum dish, over the water-bath, and the residue is incinerated at a rather low temperature and weighed. By this process, the tartrates and malates contained in the wine are converted with carbonates. The ash of normal wine consists of potassium sulphate, carbonate, phosphate and chloride, sodium chloride, calcium carbonate, etc., but, in many samples, it will be found to be largely if not entirely composed of sulphates, which is due to the practice of sulphuring and plastering.[102] Generally speaking, the proportion of ash in genuine wine ranges from 0·15 to 0·30 per cent.

Chlorine.—100 c.c. of the sample are neutralised with sodium carbonate, evaporated to dryness, and the residue gently ignited. It is then extracted with boiling water, filtered, and the chlorine determined by means of silver nitrate, either volumetrically or gravimetrically.

Sulphuric Acid.—100 c.c. are acidulated with hydrochloric acid, the liquid heated to boiling, and the sulphuric acid precipitated by barium chloride. The precipitate is well washed, dried, and weighed. 100 parts represent 42·49 parts H2SO4. Pure wine contains from 0·109 to 0·328 gramme of monohydrated sulphuric acid per litre (corresponding to 0·194 to 0·583 gramme potassium sulphate). The presence of an excess of this maximum amount indicates that the wine has been plastered.

Phosphoric Acid.—100 c.c. of the wine are evaporated, the residue ignited, dissolved in a little water, acidulated with nitric acid, and then added to an excess of solution of ammonium molybdate. After standing over night the separated precipitate is dissolved in ammonia and the phosphoric acid determined by means of an ammoniacal solution of magnesium sulphate. 100 parts of the precipitate thus obtained correspond to 63·96 parts of phosphoric acid. The former belief that the best qualities of wine contain the largest proportion of phosphoric acid does not appear to be invariably correct.

Salicylic Acid.[103]—The determination of this acid is accomplished as follows:—100 c.c. of the sample are repeatedly agitated with chloroform, which is subsequently separated and evaporated to dryness. The residue is re-crystallised from chloroform and weighed; its identity can be established by dissolving it in water and adding solution of ferric chloride (see p. 149).

Sulphurous Acid.—For the detection and estimation of sulphurous acid, the following methods have been recommended:—500 c.c. of the wine are placed in a flask, the exit-tube of which dips into a test-tube which is suitably cooled, and subjected to distillation. When about 2 c.c. have distilled, a few drops of a neutral solution of silver nitrate are added to the distillate: in presence of sulphurous acid, a white curdy precipitate will be formed, which differs from silver chloride in being soluble in nitric acid. According to Haas,[104] this test is not invariably decisive, as pure wine may cause the precipitation under certain conditions; moreover, acetic acid is said to render silver nitrate turbid in strong alcoholic solutions. Sulphurous acid can be quantitatively determined by adding phosphoric acid to 100 c.c. of the wine, and distilling it in an atmosphere of carbonic acid gas. The distillate is received in 5 c.c. of normal iodine solution. When one-third of the sample has passed over, the distillate (which should still contain an excess of free iodine), is acidulated with hydrochloric acid, and the sulphuric acid formed precipitated with barium chloride.

Colouring matters.—Very numerous processes have been published for the detection of foreign and artificial colouring matters in wine. Among those suggested are the following:—

1. A few drops of the sample are placed in succession on the smooth surface of a piece of white calcined lime, and notice taken of the tint produced. The following colours are stated to occur with pure and artificially coloured wine:—

2. If ammonium hydroxide be added to the suspected sample to distinct alkaline reaction, then a little ammonium sulphide and the liquid filtered, the filtrate from genuine wine will possess a green tint, whereas that obtained from artificially coloured wine will exhibit other colours, such as red, blue, violet, or brown.

3. 100 c.c. of the wine are evaporated to about one-half of the original volume, ammonium hydroxide added to alkaline reaction, and the liquid thoroughly shaken. Ether is then added, and the mixture again well shaken. It is next introduced into a separator, and allowed to stand at rest until the ether has risen to the surface, when the lower stratum is drawn off, and the residual ether washed by agitation with water, which is subsequently removed. The ethereal solution is now transferred to a flask connected with a Liebig’s condenser, a piece of white woollen yarn introduced into the liquid, and the contents of the flask distilled at a gentle heat: in presence of the smallest amount of fuchsine, the wool will acquire a very perceptible reddish hue.

4. A slight excess of ammonium hydroxide is added to 50 c.c. of the wine, a piece of white woollen fabric introduced, and the liquid boiled until the alcohol and ammonia are expelled. By this treatment it will be found that most aniline colouring matters, if present, become attached to the wool. Their presence can be corroborated by removing the fabric, washing and pressing it, and then dissolving it, with constant stirring, in a hot solution of potassium hydroxide. When solution has taken place, the liquid is allowed to cool, and one-half its volume of alcohol is added, then an equal volume of ether. The mixture is vigorously shaken, and, after remaining at rest for some time, the supernatant ethereal solution is removed, introduced into a test-tube, and a drop or two of acetic acid added. In presence of fuchsine, its characteristic colour will now become apparent. Methyl violet and aniline blue are separated by an analogous process.

5. Logwood and cochineal may be detected by agitating 100 c.c. of the suspected wine with manganic peroxide, and filtering. The filtrate afforded by pure wine will be colourless.

6. In DuprÉ’s process,[105] cubes of jelly are first prepared by dissolving 1 part of gelatine in 20 parts of hot water, and pouring the solution into moulds to set. These are immersed in the wine under examination for 24 hours, then removed, slightly washed, and the depth to which the colouring matter has permeated is observed: pure wine will colour the gelatine very superficially; the majority of other colouring principles (e.g. fuchsine, cochineal, logwood, Brazil wood, litmus, beetroot, and indigo) penetrate the jelly more readily and to a far greater degree. Dilute ammonium hydroxide dissolves from the stained cake the colouring matter of logwood and cochineal, but not that derived from fuchsine or beetroot.

7. The colouring principle of genuine wine when subjected to dialysis, does not pass through the animal membrane to any decided extent, while that of logwood, cochineal, and Brazil wood easily dialyses.

8. Many of the foreign dyes added to wine are precipitated by a solution of basic plumbic acetate. The precipitate obtained upon treating 10 c.c. of the sample with 3 c.c. of this reagent is collected on a filter and washed with a 2 per cent. solution of potassium carbonate, which dissolves cochineal, sulphindigotic acid and aniline red. The latter is separated upon neutralising the solution with acetic acid, and shaking with amylic alcohol, which, in its presence, will acquire a rose colour. The liquid is next acidulated with sulphuric acid, and again agitated with amylic alcohol, by which the carminamic acid, originating from cochineal, is isolated. Any remaining indigo (as well as the carminamic acid) is to be subsequently identified by means of its spectroscopic reactions. Upon treating the portion of the plumbic acetate precipitate which remains undissolved by potassium carbonate with a dilute solution of ammonium sulphide, the colouring matter of pure wine and of logwood is dissolved. If, in presence of logwood, the original sample is shaken with calcium carbonate mixed with a little calcium hydroxide solution and filtered, the filtrate will exhibit a decided red tint, but, if the wine treated be pure, little or no coloration will be produced.

9. An artificial colouring for wine, known as rouge vÉgÉtale, is not uncommonly employed. According to Amthor,[106] its presence can be recognised as follows:—100 c.c. of the wine are distilled until all alcohol is removed. The residual liquid is strongly acidulated with sulphuric acid, and agitated with ether. Some woollen yarn is next introduced into the ethereal solution, which is then evaporated over the water-bath. In presence of rouge vÉgÉtale, the wool will acquire a brick-red colour, which turns violet upon treatment with ammonium hydroxide.

10. Cauzeneuve and Lepine[107] state that acid aniline red, “naphthol-yellow S,” and roccelline red are harmless, whereas safranine and ordinary Martius’ yellow are decidedly poisonous.

The presence of “Bordeaux red”[108] is recognised by first adding sodium sulphate to the suspected wine, then a solution of barium chloride: the artificial dye is carried down with the precipitated barium sulphate, from which it can be extracted by means of sodium carbonate solution. The brownish-red liquid thus obtained acquires a deep red colour if acidulated with acetic acid, which it readily communicates to silk upon boiling. Natural red wine fails to produce a coloration under the same circumstances.

For the detection of the presence of artificial colouring matter the following process is used in the Municipal Laboratory in Paris:—Preliminary tests are made—

1st. By soaking pieces of chalk in an aqueous solution of egg-albumen; these are dried and applied for use by dropping a little of the wine upon them, and noting the coloration produced. Natural coloured wine usually causes a greyish stain, which, in highly coloured varieties, may verge to blue.

2nd. Baryta water is added to the wine under examination until the mixture acquires a greenish hue, after which it is shaken with acetic ether or amylic alcohol. If the wine be pure, the upper layer remains colourless, even after acidulation with acetic acid; whereas, in presence of basic coal-tar dyes, such as fuchsine, amidobenzole, safranine, chrysoidine, chrysaniline, etc., characteristic colorations will be obtained.

3rd. A few c.c. of the sample are made alkaline by the addition of dilute potassium hydroxide, some mercuric acetate added, and the mixture agitated and filtered. With pure wines, the filtrate is colourless; in the presence of acid coal-tar derivatives, it is red or yellow.

The general character of the artificial dye contained in the wine having been ascertained by the foregoing tests its more precise nature is determined as follows:—

In case the foreign colouring is basic, the supernatant layer obtained in the second test is separated, and divided into two portions; one portion being evaporated with pure woollen yarn, the other with filaments of silk. The dyed threads are then subjected to the following tests:—

(a) Rose-aniline or safranine affords a red coloration; safranine usually attaches itself only on silk.

(b) Soluble aniline violet produces coloured threads which become green upon treatment with hydrochloric acid, the primitive colour reappearing upon dilution with water.

(c) Mauve-aniline gives a colour which turns blue upon addition of the acid.

(d) Chysotoluidine causes a coloration which is only slightly affected by the acid, but which is discharged upon boiling with zinc powder; upon protracted exposure to the air the colour reappears.

(e) Chrysoidine and Amidonitrobenzole produce yellow colours, the former turning poppy-red if treated with sulphuric acid, the latter, scarlet. A general characteristic of dyes, similar to rose-aniline, is that they are decolorised by treatment with sodium bisulphite.

If the presence of an acid coal-tar dye is indicated by the third preliminary test, the following special methods of procedure are employed:—

Two portions of the wine are saturated respectively with hydrochloric acid and with ammonium hydroxide water, and each portion is strongly agitated with acetic ether. The ethereal layers are removed by means of a pipette, then mixed together, evaporated to dryness, the residue obtained treated with a drop of concentrated sulphuric acid, and observations made of the colour obtained:—

The method employed in the Paris Municipal Laboratory for the detection of dried fruit wine, or of added commercial glucose, is substantially the following:—A little beer-yeast is added to 300 c.c. of the suspected wine, and the mixture is allowed to undergo fermentation at a temperature of about 30°. When the fermentation is completed, the filtered liquid is introduced into a dialyser, the outer water of which is automatically renewed. The process of dialysis is continued until the outer water ceases to show a rotary effect when examined by the polariscope, after which it is neutralised with calcium carbonate and evaporated to dryness over the water-bath, with constant stirring. The residue obtained is treated with 50 c.c. of absolute alcohol and filtered, the insoluble matters being twice washed with 25 c.c. of alcohol. The alcoholic filtrates are next decolorised by means of animal charcoal, and evaporated to dryness, and the solid residue is dissolved in 30 c.c. of water and polarised. Genuine claret, when tested in this manner, fails to exhibit a rotary power, or is but slightly dextrogyrate, whereas fruit wines, and those containing artificial starch sugar, strongly rotate respectively to the left or to the right.

The following are some of the conclusions arrived at by a commission, appointed by the German Government, to inquire into uniform methods for wine analysis, and establish standards of purity for genuine wine.[109]

(a) After deducting the non-volatile acids, the extract in natural wine should amount to at least 1·1 gramme per 100 c.c.; after deducting the free acids, to at least 1 gramme per 100 c.c.

(b) Most natural wines contain one part of ash to every 10 parts of extract.

(c) The free tartaric acid should not exceed 1/6th of the total non-volatile acids.

(d) The relation between the alcohol and glycerine varies in natural wines between 100 parts alcohol to 7 parts glycerine, and 100 parts alcohol to 14 parts glycerine. These proportions do not apply, however, to sweet wines.

(e) Genuine wines seldom contain less than 0·14 gramme of ash, nor more than 0·05 gramme of sodium chloride per 100 c.c.

According to the analyses of Moritz, the maximum and minimum relative proportions of the constituents of natural wine are as follows:—The extract (after deducting the free acids) ranges from 1·10 to 1·78 per cent.; the proportion of ash to extract varies from 1 : 19·2 to 1 : 6·4; that of phosphoric acid to ash ranges from 1 : 12·3 to 1 : 10·49; that of alcohol to glycerine, from 100 : 12·3 to 100 : 7·7.[110] From the investigations of Dr. DuprÉ, it would appear that in genuine unfortified wines, the amount of alcohol present varies from 6 to 12 per cent. by weight. A wine containing less than 6 per cent. would be unpalatable, and more than 13 per cent. cannot well be present, since natural grape-juice does not contain the quantity of sugar requisite for the production of a greater amount of alcohol; moreover, an excess of this proportion would retard, if not entirely stop, the process of fermentation. Pure wines contain a greater proportion of volatile than fixed ethers, but in fortified wines the reverse is frequently the case. In natural wines, which are not over a few years old, the sugar present rarely amounts to 1 per cent., generally it is much less. Fortified wines, in which fermentation has been checked by the addition of alcohol, often contain 5 per cent. of sugar; champagnes usually show from 4 to 10 per cent., and, in some liqueur wines, a maximum of 25 per cent. has been found. In natural wines, the total dry residue generally ranges from 1·5 to 3 per cent., while in fortified wines the addition of sugar and other substances may increase its proportion to 10 per cent., or even more. At the Paris Municipal Laboratory the following standards are adopted: The amount of added water in all wines, not sold as of a special or abnormal character, is calculated on a basis of 12 per cent. of alcohol (by volume) and 24 grammes of dry extract per litre. The proportion of potassium sulphate in unplastered wines must not exceed 0·583 gramme per litre. The use of salicylic acid is prohibited.