264 INTERNATIONAL CONGRESS OF VITICULTURE 



with tenth normal alkali using phenolphthalein as an indicator. The equiva- 

 lent in terms of acetic acid is then calculated from the c. c. of N/10 of alkali 

 used; 1 c. c. being equal to .006 gins, acetic acid. A method in use in the 

 laboratory of the Italian Swiss Colony and the California Wine Association 

 laboratory depends on distilling a 50 or 60 c. c. sample of wine directly 

 without steam distillation and as the distillation progresses, the liquid dis- 

 tilled off is replaced by distilled water which is allowed to drop slowly into 

 the distillation flask at about the rate the wine distills over, 250-300 c. c of 

 distillate is collected and titrated as in the official method. This apparatus 

 has the advantage of compactness and convenience. Probably, in effect, 

 this may be a steam distillation because as soon as the alcohol of the wine 

 is volatized, the extract of the wine raises the boiling point above that of 

 distilled water. As the drops of distilled water meet this relatively high 

 boiling liquid the water is vaporized and causes bubbles of steam to escape 

 through the liquid and in this way carry over the acetic acid, which boils 

 above 100 C. 



The simplified method to be discussed in this paper is not a strictly new 

 idea but an improvement on an old one. The method is essentially one of 

 estimating the total acid in the untreated wine; then in the wine after driv- 

 ing off the acetic acid and in calculating the volatile acid by difference. 

 Directions for making the test in this way recommend taking a small sample 

 and evaporating to a syrupy consistency several times on the water bath, 

 diluting and titrating with N/10 alkali. The difference between this and the 

 total acid of the untreated wine represents loss due to volatile acid; taking 

 into account, ot course, that total acid is calculated as tartaric and volatile 

 acid as acetic. This method is slow, requires the use of a water bath, and 

 experience has shown it to be inaccurate, especially for red wines, where 

 the color interferes with the titration. 



The Method. 



In the modification of this method a 75 c. c. sample, more or less, of 

 the wine is decolorized with bone black free from carbonates. "Eponit," a 

 pure form of vegetable charcoal freed from carbonates and in use in France 

 for commercial decolorization of wines gave the best results. Impure bone 

 black is worse than useless and cannot be used for this volatile acid test. 

 The decolorized wine is filtered and should be water white. A 20 c. c. sample 

 is titrated, using phenolphtholein indicator, and the c. c. of N/10 alkali used 

 recorded. Call this "a". Then 20 c.c. is taken and mixed with approximately 

 2 gms. common salt NaCL in a 200 c. c. Erlenmeyer flask. The liquid is 

 boiled down rapidly on a gas flame or alcohol flame until a copious separation 

 of NaCL takes place and the wine begins to spatter. This gives an unmis- 

 takable point at which to stop. To the flask is now added 20 c. c. distilled 

 water and boiling repeated till NaCL separates again. The liquid is diluted 

 with distilled water and titrated with N/10 alkali using phenolphtholein 

 indicator. C. c. used are recorded. Call this figure "b". Then 



(a-b) x .03 volatile acid gms. per 100 c. c. 



The factor .03 comes from a consideration of the following facts: 

 1 c. c. N/10 alkali = .006 gms. acetic acid. If a 60 c. c. sample were 



c.c alkali X .006 



used the factor would be .01 because X 100 becomes c. c. 



60 



