FIFTH ANNUAL YEAR BOOK — PART VI. 587 



50' to 90' F. as where it was from 45^ to 65'^ F. The percentage of acid 

 formed at lower temperatures never became as great as at higher tempera- 

 tures, though part of the apparent increase in the warm room was due to 

 evaporation of the water. The best results were secured at temperatures 

 of 65= to 70' F. 



It is the ordinary practice to add vinegar, especially vinegar containing 

 ' 'mother," to the barrels in which vinegar is making; and the investigation 

 proved the practice a most excellent one, as the acetic fermentation was 

 more rapid and more complete in every case where this form of inoculation 

 or "seeding" was used. This addition of ''mother" is comparable to the 

 addition of a "starter" in souring milk, for the ''mother" is produced by 

 the growth of the acetic bacteria in the presence of air and contains large 

 numbers of these bacteria, 



It appears to be of advantage in some cases^to draw off the clear portion 

 of the cider after alcoholic fermentation has been completed, leaving the 

 dregs; and to continue the process in new clean barrels or to wash out the 

 settlings and return the clear liquid to the barrels. This proved of consider- 

 able advantage in the case of vinegars stored at low temperatures, but of 

 less utility when the vinegar was stored at higher temperatures where 

 the acetic fermentation proceeded rapidly. Possibly with cider made 

 from uncleaned apples and carelessly strained juice the results along this 

 line would be more striking; for the liability to contamination with undesir- 

 able germs would be greater in such cases. 



In both alcoholic fermentation and acetic fermentation, the air should 

 have free access, especially in the latter; for, as can be seen by the equation 

 given to explain the process, oxygen must be added to alcohol to make the 

 acetic acid and this must come largely from the air. On this account the 

 barrels should not be filled more than two- thirds or three-fourths full with 

 the apple juice, or with the "hard" cider. But when the acetic fermenta- 

 tion has ceased to be active and the amount of acetic acid is safely above 

 four and one-half per cent the vinegar should be drawn from the barrels and 

 strained, the barrels cleansed, the vinegar returned filling the barrels full, 

 and the bung driven in tight. 



Unless this is done, destructive fermentation may begin and the acetic 

 acid decrease instead of increasing. In several experiments where the vine- 

 gar was held in loosely stoppered casks or bottles, it lost all or nearly all its 

 acid, and in some cases actually became alkaline in reaction. This destruct- 

 ive fermentation may be due to new species of bacteria introduced, or even 

 in some cases to the same acetic-acid-forming species which, when the 

 alcohol is exhausted, attack the acetic acid itself. 



As showing how complex may be the processes passing in vinegar, the 

 case may be cited of four one-quart bottles of the same juice stored under 

 the same general conditions. At the end of five years bottles a and b con- 

 tained 5.74 and 5.44 per cent, respectively, of acetic acid, bottle c 2.10 per 

 cent and bottle d gave an alkaline reaction. Bottles a and c contained nearly 

 three times and bottle b two and one-half times as much solids as bottled. 



The acid of fresh apple juice is not the acid of vinegar, but a fixed acid 

 called malic acid. This has certain chemical characteristics which make it 

 quite easily recognizable; and so its presence in vinegar has been considered 

 an index to determine whether the vinegar were or were not truly vinegar 



