EXPERIMENT STATION BULLETINS. 



507 



thus allowing the alcoholic fermentation to start and proceed more or 

 less rapidly at first. Then the cider barrel is generally placed in an 

 unheated cellar, barn or outbuilding, and as the cold weather sets in, 

 the alcoholic fermentation is checked and perhaps finally stops entirely. 

 Because of the fluctuating temperature which becomes lower as the sea- 

 son progresses the alcohol fermentation takes three to six months and 

 even longer to reach completion. During this time any undesirable 

 organisms present, which are favored by the low temperature, are de- 

 veloping, using most of the alcohol and remaining sugar; and by the 

 time the alcoholic fermentation should be complete and the acetic fer- 

 mentation start spontaneously, nothing happens, as the food material 

 from which Bacterium acetl makes acetic acid, is exhausted. The liquid 

 which was originally sweet cider is nameless; it is neither sweet nor 

 "hard" cider, and never will "turn" into vinegar even if a favorable 

 temperature is established unless sufficient alcohol or source of alcohol 

 (sugar) remains and the right micro-organisms are present; this can 

 be determined only by chemical and bacteriological analysis. 



Fig. 5. Vinegar Barrel. L. surface of liquid; O, O, openings for circulation of air; F, funnel inserted 

 through stopper in bung-hole, and t, glass tube fastened to funnel with rubber tubing, for introduc- 

 ing new supplies of fermented cider without disturbing the surface film; E, glass tube to show level 

 of liquid and for drawing off vinegar. Keep this plugged with cotton to prevent the entrance of 

 insects. (Fig. 142 from Marshall's Microbiology, 1917). 



The most beneficial and practical range of temperature for the yeast 

 to grow and produce alcohol is between G5 degrees and 75 degrees 

 Fahrenheit. At temperatures much higher, there may result a loss of 

 alcohol by evaporation. Happily the same range of temperature is very 

 beneficial and practical for the acetic fermentation, thus the barrels of 

 "hard" cider need not be disturbed if the temperature of storage can 

 be regulated within these limits. 



The yeasts and bacteria responsible for the formation of vinegar are 

 plants, and like plants, must, have a favorable climate (temperature), 

 proper foods (sugar and alcohol respectively) in the soil (fruit juice, 

 etc.) in which they grow, and the soil must be practically free from 

 weeds (undesirable yeasts and bacteria) before the desirable plants 

 can grow to the best advantage. 



