LACTIC ACID FEKMENTATION 207 



microorganisms belonging to the genus Bacterium, perhaps 

 secondarily by organisms of the genus Lactouacillus, ensues. 

 Gas is given off in considerable quantities. Among the 

 gases developed are considerable quantities of those con- 

 taining sulphur, particularly hydrogen sulphide. It may 

 be noted that cabbage contains appreciable amounts of 

 glucosides containing sulphur. These are largely broken 

 down during the process of fermentation. Finally the lactic 

 acid content of the brine rises to a point which will inhibit 

 the growth of all microorganisms which are not aerobic. 

 Sauerkraut thus prepared will keep for a considerable 

 length of time if not exposed to atmospheric oxygen. When 

 so exposed, however, it rapidly molds, the lactic acid is 

 oxidized and decay occurs. 



Other Fermented Foods. Sweet corn, beets, and some 

 other foods are occasionally preserved in a manner similar 

 to sauerkraut. When mixed with a suitable amount of salt 

 and pressed firmly into jars or barrels, lactic acid fermenta- 

 tion will occur and effectually preserve the food material as 

 long as it is not in contact with the air. 



Lactic Acid in Yeast Manufacture. A medium some- 

 what acid is usually required in the production of commer- 

 cial yeast in order to prevent the development of undesir- 

 able microorganisms. Certain bacteria, members of the 

 genus Lactobacillus, are usually introduced into the vats 

 preliminary to the growth of yeasts in the commercial 

 manufacture of compressed yeast or dried yeast cakes. 



Lactic Acid in Bread Making. The bacteria present in 

 yeast cakes and in flour usually bring about the develop- 

 ment of some lactic acid during the leavening process in 

 the bread. The texture of the loaf and its flavor are in part 

 dependent upon the development of the lactic acid. Fur- 

 thermore, the keeping quality of the bread is directly 

 related to it. If sufficient lactic acid does not form during 

 the leavening process the bread is very apt to become ropy 



