4 BULLETIN 335, U. S- DEPARTMENT OF AGRICULTURE. 



acid to form malates of potassium, calcium, or magnesium. The 

 formation of these salts would still further reduce the acidity of the 

 juice. 



There is a further consideration which enters into the relative acid 

 content of green and ripe fruit — that of the dilution of the acidity 

 by ah increase of the sugar and water content. An attempt to deter- 

 mine the extent to which this change affects the percentage of acid 

 content was undertaken in 1912 and is treated in a section of this 

 report. 



It appears, then, that there are a number of changes in the compo- 

 sition of the fruit during its development and ripening which tend 

 to lower the acid content. Therefore, grapes which originally con- 

 tained a high total acidity might in many cases mature so as to reduce 

 the final acid content of products made from them. The prime points 

 of consideration for wine making are that the fruit should be well 

 ripened, so that all of the combinations of the bases with the acids 

 which are possible may be carried to completion and that malic acid 

 may be eliminated by growth processes to the fullest extent prac- 

 ticable. Then the cream of tartar in the expressed juice, whether 

 it be used for unfermented fruit juice or for wine, should be pre- 

 cipitated as perfectly as possible. If malic acid is present in any 

 quantity in wine it will be largely changed by after-fermentation 

 into lactic acid, if proper conditions are observed. 



Then a grape may be said, in a manufacturing sense, to be ready to 

 harvest at that period in its development when the sugar content 

 and the acid elements have reached the most favorable state (con- 

 sidering the purpose for which it is intended) that is possible for 

 the variety in the particular season, location, and other prevailing 



conditions. 



SOURCES AND PREPARATION OF SAMPLES. 



During the years 1911 and 1912 a certain number of plants of each 

 variety investigated were reserved for the samples desired. These 

 plants were selected with a view of guarding a quantity of average 

 fruit so that the sampling might be done in a manner to secure typical 

 material. The work of this laboratory on grape samples during the 

 past four years has shown that it is not possible to select two samples 

 of fruit at the same time which shall be exact duplicates. It is also 

 true that one can not select samples from the same vines at different 

 dates which will give results entirely logical in the sequence of the 

 changing constituents. The analyses herein reported show the effect 

 of these variations in sample, but these are not such as to confuse the 

 results. 



The 1911 samples of Catawba, Delaware, Ives, and Norton, exam- 

 ined at Sandusky, Ohio, were taken from a vineyard at Venice, 

 about 3 miles west of Sandusky. The soil is heavy black loam over- 



