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:—
| (a) | Roccelline | affords a violet colour. |
| (b) | Bordeaux, R. and B. | „ blue „ |
| (c) | Panceau R., R.R., R.R.R. | „ scarlet „ |
| (d) | Panceau, B. | „ red „ |
| (e) | Biebrich red | „ green to violet colour. |
| (f) | Tropeoline, O.O.O. | „ red colour. |
| (g) | Tropeoline, O., and Chrysoidine | „ orange-yellow colour. |
| (h) | Tropeoline, O.O. | „ violet-red „ |
| (i) | Eosine | „ yellow „ |
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.