FOODS NUTRITION. 899 



A study of the chemistry of home-made cider vinegar, L. L. Van Slyke 

 (New York State Sta. Bui 258, pp. 489-494).— An extended scries of investigationa 

 was undertaken to learn why many home-made cider vinegars fail t<> reach the legal 

 standard of 4.5 per cent acetic acid and 2 per cent cider-vinegar solids. 



The work has included the analysis of 122 samples of apple juice, representing 83 

 varieties of American-grown apples, studies of the changes which apple juice under- 

 goes during alcoholic and acetic acid fermentations, the conditions affecting these 

 changes, and studies of the destructive fermentation which vinegar undergoes on 

 long standing. On an average the apple juice as analyzed had a specific gravity 

 of 1.056 and contained 13.28 per cent solids, 7.41 per cent reducing sugars, 3.28 per 

 cent sucrose, 0.29 per cent ash, and 0.51 per cent fixed acid (malic). 



Sugar, the most important constituent in the manufacture of cider vinegar, is, the 

 author states, dependent upon the variety of the apple and the stage of ripeness, 

 unripe or overripe fruit containing less than ripe apples. In the experiments reported 

 apple juice was fermented in casks and bottles under a variety of conditions, some 

 of them approximating those commonly obtaining in the home manufacture of cider 

 vinegar by farmers. Under the ordinary conditions of cellar temperature most of the 

 sugar in the apple juice was changed into alcohol in 5 or 6 months. 



In the studies reported the temperature has ranged from 45 to 85° F., and it was 

 found that the alcoholic fermentation has taken place most rapidly at the higher 

 temperatures. Adding yeast to the apple juice hastened alcoholic fermentation. At 

 cellar temperatures the acetic fermentation took place slowly, requiring about 18 

 months. Under the experimental conditions the formation of acetic acid was most 

 satisfactory at temperatures ranging from 65 to 75° F. The addition of vinegar con- 

 taining mother to cider after the alcoholic fermentation was completed increased the 

 rapidity of acetic acid formation. When the clear portion of cider was separated 

 from the sediment, the fermentation of acetic acid was apparently favorably affected, 

 especially at lower temperatures. 



Several organisms have the power of decomposing dilute acetic acid and thus 

 destroying the value of vinegar. Since these organisms work only in the presence of 

 air, the author points out that this destructive change may be prevented by exclud- 

 ing the air after the acetic acid formation is finished. "In practice this can be done 

 by drawing off the clear vinegar, placing it in a clean barrel, filling it as full as pos- 

 sible, and putting the bung in tight." 



It was found that malic acid decreased during the process of vinegar making, in 

 most cases only small amounts, free or combined, being left when the vinegar had 

 be.ome a commercial product. In decomposed vinegars malic acid had entirely 

 disappeared. Malic acid added to apple juice also disappeared rapidly. In sterilized 

 juice the decrease of this constituent was less marked. In the experiments reported 

 all the vinegars gave a precipitate with lead acetate, yet there were some in which 

 not a trace of malic acid was present. The conclusion is reached, therefore, that 

 further study is needed of the relation of malic acid to cider vinegar. 



It was found that during the first 3 months of fermentation at cellar temperature 

 the total solids of the vinegar decreased rapidly, but the loss was not uniform in 

 different experiments. 



"There is quite generally a decrease of solids to a point below 2 per cent, but under 

 normal conditions there is a subsequent increase. In old vinegars, standing in bar- 

 rels with the bunghole open, there is evaporation of water and a consequent increase 

 of solids. In vinegars in which a destructive fermentation of acetic acid has occurred, 

 there is also a marked loss of solids. The amount of vinegar solids may be below 2 

 per cent when the acetic acid is above 4.5 per cent." 



As regards vinegar making with respect to legal standards, the author believes that 

 there should lie no difficulty in making cider vinegar containing the required 4.5 

 per cent of acetic acid in 18 to 24 months. If very rapid fermentation is desired the 



