SS4 MICROBIOLOGY OF SPECIAL INDUSTRIES 



Large quantities have always been used as food unwittingly, either 

 for animals, which consume it in certain brewery wastes of which it 

 constitutes a large portion, or by human beings who consume it in their 

 bread. It has been estimated that the bread consumed in Germany 

 in a year contains about 147,000 tons of yeast. 



Most of the yeast produced by the fermentation industries, how- 

 ever, is wasted owing to the difficulties of transportation and con- 

 servation. Recently methods of drying waste yeast have been de- 

 vised which overcome these difficulties and it promises to become a 

 valuable form of cattle food. 



Vegetables. — Various vegetables, cabbage (sauerkraut), string 

 beans, cucumbers, etc., can be preserved by covering them with weak 

 brine and allowing them to undergo spontaneous fermentation out of 

 contact with the air. 



The vegetables are cleaned, cut into pieces of convenient size, mixed 

 with I to 3 per cent of salt and tightly packed in a fermentation vessel 

 of wood, earthenware or cement. A perforated cover is placed on top 

 and weighted down with stones. The vegetable juices are forced out by 

 the combined action of the salt and pressure and the solid matter re- 

 duced in volume one-third or one-half. 



A gaseous fermentation commences within twenty-four hours if the 

 temperature is favorable, 18° to 20°, and continues for several weeks. 

 At the end of this time the sugar in the juices has been destroyed and 

 acids, principally lactic, produced to the extent of 0.5 to i.o per cent. 

 The Uquid is then drawn off and replaced with 4 to 8 per cent of brine 

 in which the vegetables wiU keep in good condition for a long time if 

 kept from the air. 



The fermentation is due to a large number of microorganisms 

 originating on the surface of the vegetables and in ihe water. The 

 yeasts attack the sugar and exhaust the oxygen. The lactic bacteria 

 at the same time produce lactic acid. This is the principal fermentation 

 and produces the acidity to which the conservation of the mass is due. 

 Many other substances are formed by the complex fermentation, the 

 principal products being alcohol, succinic acid, volatile acids, mannit, 

 amid-bodies, carbon dioxide, hydrogen, methane and various aromatic 

 esters. 



Weiss has isolated 65 different species of bacteria from sauerkraut. 

 Most of these are probably indifferent or harmless, and some harmful. 



