EXERCISE 138 



Vinegar is made by the souring of cider or wine. 



Problem. Have microorganisms anything to do with the making of vinegar ? 



What to use. Hard cider or wine (made by allowing strained apple juice or grape juice to stand 

 uncovered in a moderately warm place for several days) ; phenol, formalin, or some other antiseptic ; 

 litmus paper ; bottles. 



What to do. Divide the cider into two parts. Leave both bottles open for several hours or over- 

 night. Into one pour a few drops of antiseptic ; shake up or stir. Close both bottles loosely with 

 cotton plugs. 



After twenty-four hours, test both with litmus paper, and smell. Test thus at intervals until you 

 are sure you have vinegar. 



Record. Describe results and explain the difference between the behaviors in the two bottles. 



Questions. 1. Why not destroy microorganisms in this experiment by boiling the cider instead of 

 poisoning it ? 



2. Why not put poison into sweet cider to prevent yeast from fermenting it into hard cider ? 



3. Why not boil fluids containing alcohol to prevent their turning sour ? 



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