In this country, the alcohol is generally expressed in terms of proof spirit for trade purposes, or as percentage by volume for general use. The other constituents are most conveniently given in grams per 100 c.c. Following the German practice, total acid and fixed acid are usually expressed in terms of tartaric acid, and volatile acidity in terms of acetic acid. In France, the acids, total, fixed, and volatile, are all evaluated as sulphuric acid; the alcohol is given as percentage by volume (or sometimes as grams per litre); and the other constituents in grams per litre. The International Conference which sat at Paris in 1911 favoured the French method of expressing results, except as regards the acids, which it was recommended should be given in terms of cubic centimetres of normal alkali per litre of wine.

We proceed now to describe the analytical operations.

Alcohol

A convenient quantity of the wine to take is 100 c.c. A little more than this is placed in a 100 c.c. flask, the temperature brought to 15.6°, and the quantity adjusted to the mark. The wine is then transferred to a distilling flask, and the measuring vessel rinsed with about 40 to 50 c.c. of water, which is added to the main quantity. About 90 c.c. are distilled over into the 100 c.c. flask, the temperature again adjusted to 156°, and the volume made up to the original bulk with distilled water at the same temperature. The proportion of alcohol is then obtained in the usual manner from the specific gravity of the distillate.

With ordinary sound wine, the quantity of volatile acid distilling over does not appreciably affect the specific gravity of the distillate, but if the wine is more than usually acid the distillate should be neutralised and redistilled.

Occasionally, frothing will occur during the distillation. A little tannin added to the wine will obviate this; but the addition should not, of course, be made if the residue in the flask is required for the determination of the "extract."

Extract

Make up the residue in the distilling.flask to the original volume at 15.6°, and determine its specific gravity (water = 1000). Deduct 1000 from this, and multiply the remainder by the corresponding factor taken from the following table. The result gives the grams of extract per 100 c.c. of the wine: -

Example: - Specific gravity of residue in flask = 1026.3, say. Deducting 1000, remainder = 263. The corresponding factor in the table is 02584, this being the one opposite 25, the nearest remainder to 263. Then the extract = 263 X 02584 = 680 grams, per 100 c.c., to the nearest second decimal.

The specific gravity of the residue may also be calculated from that of the original wine and that of the distillate. If S1 and S2 be these respective specific gravities, then: -

Specific gravity of residue = 1000 +S1 - S2.

When the proportion of extract is less than 4 grams per 100 c.c, it may be determined with somewhat more accuracy by direct weighing according to one of the methods described below.

In fully fermented wines, the amount of extract approximates to 2 per cent. as a mean value, the ordinary range being from about 1.3 to 2 5, though both lower and higher values are met with. The proportion varies somewhat with the district, the year, the age of the.vine, the age of the wine, and the method of preparation.

On the Continent, much importance is attached to the value of the ratio allcohol/extract as indicating added suger or added alcohol

Consequently, a good deal of attention has been given to methods for determining the proportion of extract. In France, two processes are official; but one of them - the determination in vacuo -

K K requiring, as it does, from four to six days for its completion, has largely fallen out of use. The other method is the direct determination by evaporation of the wine and drying the residue at 100°. By reason of the volatilisation of glycerol and the oxidation of tannins and colouring matters during the drying, it is necessary to proceed under fixed conditions if results comparable with recorded values are to be obtained. Hence the reason for the following stipulation of details.

French official process; "extract at 100°." - Twenty c.c. of the wine are measured into a platinum capsule having a flat bottom, and with a diameter of 5 5 cm. and a depth of 2 5 cm. The capsule is placed on a steam-bath over an aperture of 5 cm. diameter, and the evaporation continued for six hours, at the end of which time the vessel is wiped, allowed to cool in a desiccator, and weighed. German official process. - In Germany, the method of drying at 100° is also official for wines containing less than 4 per cent. of extract, but instead of being dried for six hours the sample is evaporated on the bath during about forty minutes only, until of the consistency of a stiff syrup, and then dried in the oven for two and a half hours. Fifty c.c. of the wine are taken if the percentage of extract does not exceed 3; if between 3 and 4 a smaller volume is employed, such that not more than 15 grams of extract are present. The platinum capsules employed are of 85 cm. diameter, 2 0 cm. depth, and 75 c.c. capacity, weighing about 20 grams; the apertures of the steam.bath are of 6 cm. diameter. For the preliminary calculation, in order to decide how much wine to take, it is necessary to know the specific gravity of the wine deprived of its alcohol. This may be obtained, as shown above, by deducting the specific gravity of the distillate from that of the original wine + 1000. The specific gravity 10155 corresponds with 4 grams, and 1011.6 with 3 grams, of extractives in 100 c.c. of the wine.

For wines with more than 4 per cent. of extract the proportion is deduced from official tables, which show the quantity of extract corresponding with the specific gravity of the de-alcoholised wine. Total acidity. - Twenty.five c.c. of the wine are heated to the commencement of ebullition to expel carbon dioxide, and titrated whilst hot with decinormal alkali, using litmus paper as indicator. The results are usually expressed in terms of tartaric acid (in France as sulphuric acid); 1 c.c. N/10.alkali = 0'0075 gram of tartaric acid.