THE MANUFACTURE OF OTHER FERMENTED PRODUCTS 555 



When the process is successful the lactic bacteria multiply rapidly from 

 the first and quickly produce enough acidity to restrain growth of the 

 harmful kinds, among the worst of which are the butyric bacteria. 



Starch. — Starch is prepared fro^i potatoes, corn, wheat, flour and 

 other amylaceous substances. The present method of separation is 

 by chemical means. Formerly it was accomplished by a complex 

 fermentation. 



For the fermentation method, the grain is soaked in water until soft, 

 then ground and made into a paste which is allowed to ferment sponta- 

 neously or started with a leaven taken from a previous fermentation. 

 Alcoholic, lactic and butyric microorganisms attack the sugar while 

 others attack the gluten and cellulose. The fermentation lasts from 

 twelve to twenty-five days according to the temperature and the 

 resistance of the raw materials. " i 



During fermentation, lactic and butyric acid, hydrogen sulphide, 

 ammonia and carbon dioxide with traces of alcohol and acetic acid are 

 produced. The process is stopped as soon as gas ceases to be given 

 off and before putrid fermentation sets in. The starch which is set 

 free settles to the bottom and is separated by decaiitation, washing and 

 screening. 



The washed starch is then allowed to settle for three or four days in 

 water. The sediment that is formed consists of three layers, the top 

 consisting principally of gluten, the second~of gluten and starch and the 

 bottom of comparatively pure starch. The layers are separated and the 

 starch extracted from the two upper layers by repeated washings on 

 inclined planes. The starch, owing to its higher specific gravity, re- 

 mains near the lower parts of these planes. 



Sugar. — In the manufacture of sugar, microorganisms have no 

 useful part but many forms may be injurious and cause serious losses. 

 The juices of beets and sugar cane and the saccharine liquids obtained 

 by presses or diffusion batteries form excellent media for the multi- 

 plication of many Saccharomyces and bacteria. They are controlled 

 by cleanliness, rapidity of handling, and steriUzation by heat. They 

 are injurious by destroying sugar and thereby diminishing the yield, 

 by inverting a portion of the saccharose and rendering the crystal- 

 lization difficult and by forming gelatinous masses in the liquids. 



Many of them are very resistant to heat. S. zopfii withstands a 

 temperature of 66° for half an hour. Streptococcus mesenterioides forms 



