BACTERIA IN THE PRODUCTION OF FOOD 223 



teria, because they are not concerned in the manufacture 

 of cottage cheese except in the souring and curdling of the 

 milk. If the milk is sweet, it first has to be soured, which 

 should be done by placing it at a temperature of about 

 70 degrees for a day or two. The rest of the process is to 

 remove the curd and press out the whey. Other kinds of 

 cheeses are made from milk curdled with rennet instead 

 of by the action of bacteria, and these microorganisms 

 grow subsequently in the curd, and thus produce the flavors ; 

 but the process involved is not well adapted to home 

 manufacture. 



Butter is seldom made at home, except on the farm. 

 When it is, little attention is paid to control of the bac- 

 teria. The cream is soured (ripened) by bacterial action, 

 and after that the process of churning is mechanical. If 

 the wrong bacteria take part in the ripening, the flavor is 

 bad ; but a good flavor can be brought about without real 

 souring. In modern creameries the ripening process is 

 being continually shortened, till at present much cream is 

 churned while still sweet. 



A food-making process dependent upon bacteria which 

 the housekeeper is much more apt to undertake is the 

 manufacture of sauerkraut or dill pickles. The principle 

 involved in mating both is the same. The cucumbers or 

 the shreds of cabbage are packed in a jar, with considerable 

 salt, and allowed to stand under a weight so that the juices 

 will be extracted. Fermentation then takes place. On 

 account of the salt, few of the decomposition bacteria can 

 grow, and acid-forming types develop something like those 

 that sour milk, although not the ordinary lactic-acid bac- 

 teria. These gradually change the nature of the cabbage 



