EXPERIMENT STATION BULLETINS. 511 



largest possible amount of alcoholic liquid. lu this way a certain vol- 

 ume of alcoholic liquid is changed into strong vinegar in a few days, 

 which otherwise would take weeks and months, perhaps years to accom- 

 plish. 



VINEGAR "'"diseases." 



Off-fermentations : As has been before mentioned, the raw materials, 

 e. g., fruit juices, etc., may often not "turn" into vinegar. This is 

 jjrobably due to "off-fermentations" produced by microorganisms. The 

 only fermentations that should take place in vinegar-making are the 

 yeast fermentation by whicli the sugar is changed to alcohol, and the 

 bacterial fermentation by which the alcohol is changed into acetic acid. 

 Other fermentations may occur before, during, or after these and are 

 all to be avoided as harmful. 



Mycodermae: If a fruit juice or other liquid strong in alcohol is left 

 with its surface exposed to the air, it will usually in a few days be 

 covered with a dull whitish film, thin and smooth at first but gradually 

 becoming thicker, and finally rough and heavily wrinkled. This is 

 the growth of yeast-like microorganisms of a type called Mycodenna vini, 

 which develop only on the surface in full contact with the air, attacking 

 the acid and alcohol, changing it all finally to water and carbon dioxid 

 (gas), thus destroying the possibilities of vinegar ever being formed. 



If this growth begins to form, it may be checked merely by the 

 addition of a large quantity of a pure culture of acetic bacteria; the 

 most sure method, however, is to draw off the vinegar, scald out the 

 barrel thoroughly, heat the vinegar to 140 degrees F. to destroy the 

 Mycoderma (only the best unchipped euamelware kettles should be 

 used), return the vinegar to the barrel and when cool inoculate with a 

 pure culture of acetic bacteria. 



Acetic Bacteria: A film will often be formed on fermented fruit juices, 

 etc., especially those low in alcohol, which is thinner, smoother, and more 

 or less glistening, consisting of bacteria. These are the acetic bacteria 

 themselves. Because of the low alcohol content the acetic bacteria can 

 manufacture only a limited amount of acetic acid, but still needing more 

 food they oxidize this acid into useless carbon dioxid and water, and 

 again no vinegar is formed. 



If this film is disturbed or becomes heavy on account of age, it sinks 

 to the bottom of the liquid and there forms the slippery leathery mass 

 familiarly known as "mother of vinegar," In this mass at the bottom 

 of the liquid the bacteria are deprived of the oxygen of the air, and can- 

 not therefore continue to manufacture acetic acid; then other germs may 

 destroy it, producing substances of disagreeable tastes and odors, and in 

 time cause putrefaction and destroy the flavor entirely. The sinking of 

 the film may be prevented by floating it on a clean splinter of wood, or 

 if the size of the bung permits, a little raft may be made. Nails should 

 not be used in its construction. 



Liquids low in alcohol are the result of the lack of sugar which may 

 result from the use of unripe fruit; of ripe fruit low in sugar content; 

 from a too great dilution of the sugary solution (honey, syrups, and the 

 like) ; or from the presence and rapid growth of germs other than the 



