New York AGRICULTURAL EXPERIMENT STATION. 135 
5. Loss of Acetic Acid in Vinegar on Standing.—Several differ- 
ent organisms have the power of decomposing dilute acetic acid 
and thus destroying the value of vinegar. These organisms work 
only in the presence of air. Accordingly, this destructive change 
in vinegar can be prevented by excluding air, when once the acetic 
acid has been formed. In practice, this can be done by drawing 
off the clear vinegar, placing it in a clean barrel, filling it as full 
as possible and putting the bung in tight. 
6. Variations in Vinegar made under Uniform Conditions.—It 
is possible that different barrels of apple juice placed side by side 
may show quite different behavior in fermentation. 
7. Behavior of Malic Acid of Apple Juice during the Fermenta- 
tion Processes of Vinegar-making.—Malic acid was found to 
decrease during the vinegar-making process. In most cases, only 
small amounts of malic acid, free or combined, were left when the 
vinegar had become a commercial product. In decomposed vine- 
gars, malic acid had entirely disappeared. Malic acid added to 
apple juice also disappeared to a large extent. In sterilized apple 
‘juice, the decrease of malic acid was less marked. 
8. The Relation of Malic Acid to the Identification of Pure 
Cider Vinegar.—The white precipitate formed when lead acetate 
is added to vinegar has been attributed to the presence of malic 
acid in the vinegar and a vinegar failing to give this test is usually 
regarded as not cider vinegar. While all of our vinegars gave a 
precipitate with lead acetate, there were several in which no trace 
of malic acid was present. Further special study is needed of the 
relation of malic acid to cider vinegar. 
9. The Solids of Apple Juice and Cider Vinegar—During the 
first three months of the alcoholic fermentation at cellar tempera- 
ture, the solids decreased rapidly. The loss was not uniform 
in different experiments. There is quite generally a decrease of 
solids to a point below 2 per ct., but under normal conditions 
there is a subsequent increase. In old vinegars, standing with the 
bung-hole open, there is evaporation of water and a consequent 
increase of solids. In vinegars in which a destructive fermenta- 
tion of acetic acid has occurred, there is also a marked loss of 
solids. The amount of vinegar solids may be below 2 per ct. when 
the acetic acid is above 4.5 per ct. 
