EXPERIMENT STATION BULLETINS. 513 



all others. Now this same idea can be applied to other fermentation 

 industries with equally good results. For example, it lias been found 

 that wine, a product of alcoliolic fermentation, can be standardized as 

 to quality, flavor, bouquet, etc., by this very process of controlling the 

 fermentation with pure cultures of a wine yeast; bread, another product 

 of alcoholic fermentation has long been standardized by the use of 

 pure cultures of the bread j^east which are sold as yeast cakes. Thus 

 it is possible b}^ the use of good yeast cakes for the housewife to make, 

 almost without fail, a bread of uniform good quality. Why not, then, 

 carry out this idea in vinegar fermentation? There are certain types 

 of yeasts which produce much more alcohol than others out of the same 

 quantity of sugar, and there are types of acetic bacteria which can 

 manufacture a much higher percentage of acetic acid than others out 

 of the same amount of alcohol. Why not use pure cultures of these 

 best types of germs and produce a uniformly high quality of vinegar. 

 Here is where the scientist comes in. The bacteriologist knows how 

 to separate the good germs from the bad and indifferent ones, and 

 how to grow the good germs in large numbers so that they may be 

 used for a starter just as the yeast cake is used for bread-making. 

 The Bacteriological Laboratory of your State Agricultural College is 

 growing these pure cultures of yeasts and bacteria, for the very purpose 

 of furnishing them to those Avho wish to make the best quality of vinegar. 

 Two pure cultures (Fig. 7) one of a selected alcohol-producing yeast 

 and one of selected acetic-acid-producing bacteria sufficient for a barrel 

 two-thirds full of freshly expressed fruit juice or other sugary liquids, 

 are furnished in order to conti'ol the vinegar fermentation. A nominal 

 charge of twenty-five cents per culture is made to cover the cost of 

 material and shij)ping. An application blank for these cultures will 

 be found on page 49G of this bulletin. 



Addition of vinegar for controlling the acetic fermentation : When 

 the alcoholic fermentation is nearly complete, as a rule the acetic 

 bacteria which are already present start to form the film or "mother" 

 on the surface of the liquid. In order to give the vinegar a good start at 

 this stage of fermentation, many farmers have the practice of adding two 

 to four quarts of good cider vinegar containing more or less "mother," to 

 each barrel. This practice is good or bad depending on the type of 

 "mother" added. Pure "mother," i. e., that made up exclusively of acetic 

 acid bacteria, is a thin, white, glistening, gelatinous membrane that 

 forms on the surface of vinegar. It seldom becomes one-sixteenth of an 

 inch in thickness and should be translucent or white in color. On the 

 other hand, the thick, tough, dark brown, slippery, leathery masses 

 which form in vinegar and are usually regarded as "mother of vinegar" 

 consist not only of acetic acid bacteria, but of yeasts and other bacteria, 

 which may be actually harmful to the vinegar. It is to the harmful germs 

 that the bad flavor in vinegar is due; they may also cause a partial or 

 complete loss of the acid. 



OTHER VINEGAR DISEASES. 



Blackening: Vinegars, after making will often turn cloudy by the 

 formation of a fine blackish precipitate on exposure to the air. This 

 may be due to an oxidase which may be checked by adding 2 to 5 oz. 

 of potassium metabisulflte per 1,000 gallons ©f vinegar. 



