168 CIDER — PERRY. 



the wine an acid flavor. When this has once com- 

 menced, and the wine is what is technically termed 

 pricked, it is very difficult to render the wine whole- 

 some again ; wines are subject to many diseases, as 

 they are called, and some of them may be prevented 

 or remedied. The chief cause of them is, the pre- 

 sence of a minute quantity of ferment, of some kind 

 or other. When wine is not perfectly clear, it is 

 evident that it contains "ferment," and is, conse- 

 quently, peculiarly liable to ferment and turn sour. 



394. There are many other fermented liquids 

 which are prepared in the same way as wine, and, 

 like it, contain alcohol, derived from the fermentation 

 of sugar. Thus cider obtained from apples, perry 

 from pears, and mead from honey, derive the alcohol 

 which they contain from the sugar of fruit or honey, 

 and owe their flavor chiefly to the volatile oils formed 

 during its fermentation. 



395. In the preparation of these liquids, especially 

 cider, it is often necessary to put a stop to the fer- 

 mentation when it is arrived at a certain point ; this 

 is usually efl'ected by the fumes of burning sulphur ; 

 a small quantity of sulphuric acid gas arrests the 

 fermentation of a large quantity of fermenting liquid. 

 Fermentation is arrested or altogether prevented in 

 a very remarkable manner by the presence of various 

 substances, such as some of the strong acids, certain 

 salts, and some of the volatile oils, even in very 

 minute quantity. No substance possesses this power 

 to a greater degree than sulphuric acid gas (173). 



