57 MICROBIOLOGY OF FOODS 



PRESERVATION OF VEGETABLES BY FERMENTATION* 



Lactic acid is an excellent preservative and affords a very common 

 means of preserving certain kinds of vegetables. The most familiar 

 examples are sauerkraut and dill pickles. In some European countries 

 many kinds of vegetables are preserved by lactic or " kraut" fermenta- 

 tion this method replacing to a large extent preservation by can- 

 ning. String beans, greens of all sorts, cauliflower, carrots, turnips, and 

 beets are very satisfactorily preserved in this way; peas tend to become 

 rancid in flavor. 



Two general fermentation methods are used, dry-salting and 

 brine For juicy vegetables, such as cabbage and greens, the dry-salt- 

 ing method is preferable; for large vegetables or vegetables of less water 

 content fermentation in brine is advisable. Sufficient salt is sometimes 

 used to prevent all fermentation. 



In the preparation of sauerkraut the dry-salting process is used. 

 The heads of cabbage are cored, the outer leaves are removed, and the 

 remainder is cut into thin shreds. For each 100 pounds of cabbage 

 2^ pounds of salt is added and mixed with the cabbage in open wooden 

 containers varying in size from a small barrel or crock for home use to 

 tanks holding a thousand gallons or more in large factories. Pressure 

 is applied to the mixture, by weights in the household and by screw or 

 beam presses in factories. The osmotic action of the salt combined 

 with the pressure forces the juice from the cabbage. In this juice 

 a very vigorous gaseous and acid fermentation ensues in which the 

 mannite and sugars of the cabbage are converted into lactic acid, 

 acetic acid, alcohol, succinic acid (and in some cases butyric acid). 

 Carbon dioxide, hydrogen, methane and various aromatic esters and 

 other bodies are also formed. At the same time the protein is de- 

 composed more or less. Without the addition of salt a putrefactive 

 fermentation is apt to result; the salt to this degree acts as a governor 

 of the types of fermentation that occur. It tends to favor lactic fer- 

 mentation and check putrefaction. The fermented product owes 

 its keeping qualities to the lactic acid formed during the fermentation 

 period. The amount of acid formed is usually from 0.5 to 1.5 per cent. 



Mycoderma vim and molds develop rapidly, especially in warm 

 weather, on the surface of the fermented liquid and rapidly " devour' 1 



* Prepared by W. V. Cruess. 



