MICROBIOLOGY OF FERMENTED FOODS 579 



honey, various aromatic substances, and sometimes alcohol and passed 

 through another fermentation. 



The leaves are then usually tied up in bundles, partially dried, 

 pressed in boxes where a final slow fermentation occurs. During this 

 final fermentation nicotine decreases and nitrates are destroyed, while 

 ammonia and sometimes butyric acid are formed. 



It seems probable that the changes during the curing of tobacco 

 are due in the first place to hydrolyzing, proteolytic, and oxidizing 

 enzymes, and that these enzymatic changes are supplemented by the 

 bacteria which destroy nitrates and produce ammonia. It is possible 

 that these various factors account for variations in the characteristics 

 of tobacco from the same source. 



STARCH* 



Starch is prepared from potatoes, corn, wheat, flour and other 

 amylaceous substances. The present method of separation is by chem- 

 ical 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 spon- 

 taneously 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. 



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 decantation, 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 wash- 

 ings on inclined planes. The starch, owing to its higher specific 

 gravity, remains near the lower parts of these planes. 



* Prepared by F. T. Bioletti. 



