MICROBIOLOGY OF FERMENTED FOODS 571 



the lactic acid. This soon results in a reduction of the acidity to the 

 point where putrefactive organisms may develop. These acid-de- 

 stroying organisms are aerobic. Therefore, prevention of their growth 

 consists simply in excluding air from the fermented material. Tanks 

 or barrels may be filled with dilute brine and headed up; small con- 

 tainers are sealed with paraffin or vegetable oil to exclude air. The 

 sealing of the container is not done until fermentation is complete. 

 In warm weather complete fermentation will take place in eight to ten 

 days; in cool weather two to four weeks is required. Mycoderma 

 grows very rapidly in warm weather forming a heavy gray wrinkled 

 film; in cold weather it develops very slowly or not at all; hence more 

 precautions against its development must be taken during the summer 

 months than during the fall or early spring. 



Weiss has isolated some sixty-five different species of bacteria from 

 sauerkraut, most of which were indifferent or harmless. The writer 

 can see no reason why Bacillus botulinus might not develop in cabbage 

 or other vegetables during or following fermentation and suggests this 

 as a good field for investigation by the various laboratories at present 

 engaged in the investigation of B. botulinus in its relation to food 

 preservation. 



String beans and many varieties of greens may be preserved in the 

 same manner as sauer kraut. The best results are obtained if a small 

 amount of vinegar is added to the brine to favor lactic organisms and to 

 discourage putrefactive forms. 



In the manufacture of most pickles, the raw material (cucumbers, 

 cauliflower, etc.) undergoes a lactic acid fermentation before receiving 

 the final vinegar or other preservative solution or sauce. Normally, 

 the cucumbers are first placed in a brine of about 45 salometer test 

 (about 12 per cent sodium chloride) in open vats. As osmotic action 

 and fermentation proceed, the brine becomes diluted by the vegetable 

 juices; if the concentration falls much below 45 salometer, putrefac- 

 tion and softening occur. An attempt is therefore made to increase 

 the concentration to 60 salometer test (15 to 17 per cent sodium chlor- 

 ide) by progressive additions of salt. The vegetables are well covered 

 by the brine. Vigorous lactic acid fermentation occurs in the brine 

 and vegetables. Mycoderma vim and film-forming bacteria develop 

 at the surface of the liquid but are usually not sufficiently active in the 

 60 brine to reduce appreciably the acidity. Cucumbers are often 



