586 IOWA DEPARTMENT OF AGRICULTURE. 



American-grown apples, made at this station, in Washington, D. C.,in 

 Pennsylvania and in Virginia, five samples, of as many diflferent varieties, 

 were too low in sugar to produce vinegar of the required acidity. The 

 sugar in apples reaches its maximum in ripe fruit, being low both in those 

 that are green and those that are over ripe. It averaged, in the apples used 

 in the tests at this station, I3}i per cent, and varied less than two per cent 

 either above or below the average. A somewhat surprising fact to those 

 not familiar with the chemistry of the subject, is that ''sweet" apples do 

 not owe their sweetness to the large percentage of sugar but to the small 

 amount of malic acid they contain. For example, the sample of Red 

 Astrachan juice contained 10.16 per cent of sugar and 1.15 per cent of malic 

 acid; while Tolman Sweet and Sweet Bough contain about the same amount 

 of sugar, but only 0.10 to 0.20 per cent of malic acid. 



Starting, then, with juice containing sufficient sugar, what are the con- 

 ditions which will best promote the changes to alcohol and to vinegar and 

 prevent loss? The sugar must first be acted upon by the enzyms, or fer- 

 ments, which are produced by yeast plants. The yeast germs are usually 

 present everywhere, so that they pass from the surface of the apples into the 

 juice as it is pressed out, or fall into the cider from the air. It has some- 

 times been held unwise to wash apples before pressing them, for fear of 

 carrying away the necessary yeast germs; but the apples used in all the 

 station tests were washed without apparent interference with alcoholic fer- 

 mentation. If apples have become dirty it is certainly best to wash them, as 

 otherwise there is danger of introducing bacteria that interfere with proper 

 fermentation. In ordinary cellar temperature, most of the sugar is changed 

 into alcohol in five or six months, the change being slow during the first 

 month, but quite rapid during the second, third and fourth months. The 

 process may be greatly hastened by storing in rooms warmer than cellars 

 usually are during the fall and winter months. By placing bottles of vine- 

 gar in rooms of different temperature, running from SS"" to 85' F. it was 

 found that at 55° only 2i per cent of alcohol was formed in three months; 

 at 60° or 65' F. more than 4i per cent; and at 70° and 85° F. about 6i per 

 cent was formed in the same time. At higher temperatures than this, 

 evaporation of the alcohol would be liable to cause loss. 



The addition of yeast also hastens alcohol formation, so that at a tem- 

 perature of 55' F. cider with yeast added gave 6i per cent of alcohol, and at 

 70^ F., with yeast, 7i per cent, both in one month. The use of any form of 

 commercial yeast, if sufficiently fresh will probably be found to give good 

 results. 



After the yeast fermentation has been completed the acetic-acid forming 

 bacteria begin to attack the alcohol and produce acetric-acid This process 

 is ordinarily very slow for about three months after the sugar has all been 

 changed to alcohol, that is during the eighth, ninth and tenth months of 

 cellar storage; but advances rapidly from the tenth to the fourteenth month 

 and is practically completed in two years. This process also moves more 

 rapidly, when once well started, at higher temperatures; but differences of 

 temperature appear to have little effect during the three months after the 

 sugar has disappeared. Beginning with the tenth month of storage, how- 

 ever, and up to the end of two and one-half years, nearly twice as great a 

 percentage of acetic acid was produced where the temperature varied from 



