INTERPRETATION OF RESULTS. 51 



will be shown by the following extract, taken from a letter from Mr. 

 Marvin Curtis: 



Some years ago we established the precedent of rejecting all wines whose volatile 

 acid, calculated as acetic, exceeded one-fourth of the total free acid, calculated as tar- 

 taric. This we did after making many analyses, both chemical and microscopical, of 

 wines of different ages. Of course this ratio in some cases is absurd, for if a wine 

 contains 0.8 per cent of free acid and 0. 18 to 0. 20 per cent of volatile acid we would con- 

 demn it unless it was an old wine, say, of four or five years. I deprecate this method 

 of passing on a wine by proportion of volatile to free acid, as it allows too much lee- 

 way, and if you get a wine high in volatile and yet within the ratio and reject a wine 

 which is lower in volatile but of a higher ratio to the free it brings the whole sys- 

 tem into disrepute. 



But at the time of establishing this ratio there was so much bad wine made that if 

 we had attempted to make any fixed standard we would either have had to put a 

 very high figure, or reject half of the wine produced. Now, however, I think the 

 time has come to change this standard and to have a definite figure. I favor for our 

 California wines up to say, 3 years old, a maximum standard of 0.14 per cent for 

 volatile acid. This figure is fair and our wine makers can easily keep inside of it, 

 for, after all, excessive volatile acid is simply the result of carelessness in fermentation 

 and in handling the wine. The German limit of 0.12 per cent is too low for us, 

 especially for our red wines, and would work much harm. 



UNDETERMINED EXTRACT. 



The undetermined extract is obtained by deducting the sum of the 

 glycerol, ash, fixed acids, and the sugar in excess of 0.1 gram, from the 

 total extract. This figure is sometimes of value in judging of the 

 purity of a wine. As a result of his study of German wines Borg- 

 mann states that white wines should contain at least 0.30 gram per 

 100 cc, and rarely more than 0.6 gram per 100 cc of undetermined 

 extract. This is especially important in wine whose extract content 

 is very low, as in such cases it very often assists in determining whether 

 or not addition has been made to increase the percentage of extract to 

 the minimum limit. A high undetermined extract should accompany 

 a high percentage of alcohol and a low acid content. 



In American wines so few complete analyses have been made that 

 we have no knowledge of the value of the undetermined extract as a 

 criterion of their purity. 



POLARIZATION. 



( 1 ) The wine shows no rotation. 



This may be due to the absence of any rotatory body, or to the simultaneous pres- 

 ence of dextrorotatory and levorotatory sugars. 



(a) THE WINE is INVERTED. A levorotation shows that the sample contains cane 

 sugar. 



(6) THE WINE is FERMENTED. A dextrorotation shows that both levorotatory sugar 

 and the unfermentable constituents of commercial dextrose were present. 



If no change takes place in either (a) or (6) in the rotation, it proves the absence of 

 unlermented cane sugar, the unfermentable constituents of commercial dextrose, and 

 of levorotatory sugar. 



