SS6 MICROBIOLOGY OF SPECIAL INDUSTRIES 



chains of cocci surrounded by voluminous gelatinous sheaths which 

 unite in zoogleic aggregations sometimes very troublesome in sugar 

 factories. On account of its sheath it is very resistant to adverse 

 conditions. It ,retains its vitaUty after drying for three. and a half 

 years. It is not killed by heating to 86° for five minutes and occurs in 

 the hot liquids of the difiusion batteries. 



Tobacco. — To prepare tobacco leaves for the use of the smoker 

 they must be dried, fermented and aged. Unless all these processes 

 are properly carried out the tobacco does not possess the desired aroma, 

 it contains protein substances that give a bad odor to the smoke, and is 

 usually too rich in nicotin. The processes of preparation are often 

 referred to as "curing," though this term is generally restricted to the 

 preliminary drying. 



The curing is more than a simple drying, as various important 

 changes of composition take place. When young leaves are removed 

 from, the stalk and dried they lose from 12-15 P^r cent of their dry 

 weight, when dried on the stalk the loss is greater; from 14-18 per cent. 

 Riper leaves lose more, up to 35 or 40 per cent. This loss is due to 

 transpiration and to translocation of substances from the leayes to the 

 stalks and is caused by diastatic, proteolytic and other enzymes. 

 The principal changes are the disappearance of starch and reducing 

 sugar; a decrease in proteins, nicotin, pentosans and malic acid and 

 an increase in citric acid. Ammonia is formed and the changes after 

 curing are more rapid with rising temperature up to about i30°F.* 



After curing the dried leaves are piled in masses, moistened and 

 allowed to undergo a fermentation which raises the temperature to 

 So°-55°. Sometimes the leaves are then sprinkled with a solution 

 containing sugar, honey, various aromatic substances and sometimes 

 alcohol and passed through another fermentation. 



The leayes are then tied up in bundles, partially dried, and pressed 

 into boxes where another slow fermentation often takes place. 



The principal chemical changes which take place in this "curing" 

 of tobacco are a considerable diminution of the nicotin, the destruction 

 of nitrates and the production of ammonia and sometimes of butyric 

 acid. 



There are three theories as to the cause of these changes. Accord- 



* Qarner, Bacon, and Poubert, BuU. 79, U. S. Dept. gf Agr., 1914. 



