1 86 BACTERIA, YEASTS, AND MOLDS 



be checked and the pickles preserved. It is practically 

 important to know that pickles should not be kept in 

 glazed ware, since the acetic acid may imite with the 

 glazing and make miwholesome products. Metal covers 

 are especially undesirable, for the same reason. Glassware 

 receptacles are best for the holding of pickles. 



In a somewhat modified way acetic acid or lactic acid 

 is the basis of certain other preserved foods. Sauerkraut, 

 for example, is cabbage protected from putrefactive fer- 

 mentation by allowing it to sour in the presence of con- 

 siderable salt, with the production of acetic and lactic 

 acids. The acid in this case is formed in the cabbage by 

 the growth of acid-producing bacteria, and after it is 

 formed it prevents the growth of other putrefactive bacteria, 

 thus making it possible to preserve for a long time the 

 vegetable material which would otherwise undergo putre- 

 faction. Here we actually have an instance of a harmless 

 kind of microorganism protecting food from the action of 

 other species. A similar food product is sometimes made 

 from beans which are allowed to sour and are thus pre- 

 served from further decay, while dill pickles are similarly 

 made from cucumbers. 



Any substance can be preserved from bacterial action 

 if it can be soaked in vinegar or other acid, and it is there- 

 fore possible in the household to convert into either sour 

 or sweet pickles a considerable variety of vegetables. 

 In actual practice the use of vinegar for this purpose is 

 very limited, mostly confined to green fruits and vegeta- 

 bles, although fish or flesh is occasionally treated in the 

 same way. The product obtained is used as a flavor to our 

 diet rather than as a food. 



