This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
This is the most important of the fixed acids in wine. It is present partly as the free acid and partly as cream of tartar, with a small quantity of calcium tartrate. The total amount may be determined according to the French official process as follows: decanted through a small filter, and the flask and filter washed with a little of the ether-alcohol mixture. The filter is then placed in the flask, about 40 c.c. of warm water are added, and the whole digested till the precipitate is dissolved; the solution is then titrated with iV/20.alkali, phenolphthalein being used as indicator. If n be the number of cubic centimetres required, the total tartaric acid is given in terms of cream of tartar and in grams per 100 c.c. of the wine by the expression n X 0 047 + 0.02. The result may be converted into terms of tartaric acid by the factor 07979.
To 20 c.c. of the wine in an Erlenmeyer flask of about 250 c.c capacity is added 1 c.c. of a 10 per cent. solution of potassium bromide and 40 c.c. of a mixture of equal volumes of ether and alcohol (90 per cent.). The flask is closed and shaken, and then set aside for three days. At the end of this time the liquid is
1 For details, see Dutoit and Duboux, "Analyse des Vins" (Lausanne, 1912).
2 Annali Chim. Appl, 1916, 5, 233.
3 Ibid., 1918, 9, 155; Chemical Abstracts, 1918, 12, 2224.
With wines rich in sugar, it is well to use twice the quantities of alcohol and ether (40 c.c. of each) added separately. The alcohol is first well mixed with the wine, and the ether added afterwards: this avoids the separation of a syrupy layer of sugar.
By omitting the potassium bromide, the same method serves for the estimation of the cream of tartar in the wine.