MICROBIOLOGY OF ALCOHOL AND ALCOHOLIC PRODUCTS. 441 



The pectic matters vary from 2 g. to 25 g. per liter but should not be 

 too high. Pears contain usually about the same amount of sugar as 

 apples, more tannin and much less pectic substances. 



The microorganisms occurring naturally on the surface of the fruit 

 are similar to those occurring on grapes, but special forms of Saccharomyces 

 are found. Pure cultures of wine yeast are used successfully in cider 

 making where a perfectly dry cider is wanted. Where a small remnant 

 of unfermented sugar is desired, the difficulties of using pure cultures 

 have not yet been overcome. The wild yeasts occurring on the fruit in 

 large quantities usually take precedence. 



Attempts to sterilize the juice by heating have not been successful 

 owing to the production of a persistent cloudiness. It seems probable that 

 a moderate use of sulphurous acid as in the case of wine may solve the 

 dimculty. 



The principles of the control of the microorganisms, good and 

 bad, are the same as in wine making. The same care in gathering 

 and keeping the fruit and in extracting and handling the juice are 

 necessary. 



The fermentation is similar to that of wine, but the cider should be 

 taken off the yeast sooner in order to promote clarification and the re- 

 tention of a little unfermented sugar. 



Cider is subject to the same bacterial alterations as wine and requires 

 the same treatment. It is more difficult to keep when made in the ordi- 

 nary way and is usually consumed during the first year. It is particularly 

 subject to turning brown, owing to the large amount of oxidase present 

 in apple juice. 



The use of sulphurous acid for preliminary defecation, pure yeast in 

 the fermentation, and fining, followed by pasteurization soon after the 

 fermentation, seem to offer the best means of improving present methods. 



FERMENTED BEVERAGES OF VARIOUS FRUITS. 



Many other fruits, especially those rich in sugar and with moderate 

 acidity, are used locally to produce alcoholic beverages. The methods 

 of fermentation are similar to those used in wine making, but additions 

 of sugar and water are usually made to correct defects of composition. 

 Very often distilled alcohol is also added after fermentation to preserve 

 the liquid, which is thus rendered unsuitable for an ordinary beverage. 



