MICROBIOLOGY OF FERMENTED FOODS 569 



the flour, water and salt are mixed and thoroughly beaten. Similar 

 breads are made in other primitive countries. 



Salt-rising bread has been studied from the bacteriological stand- 

 point by Kohman. * A starter is prepared by scalding corn meal with 

 hot milk. Salt is added to the mixture. The mixture is kept in a warm 

 place until in active fermentation and is then mixed with wheat flour 

 and salt to give a dough of normal consistency. The organisms are of a 

 spore-bearing type which readily survives a temperature of 75, while 

 B. coli and other undesirable organisms are eliminated. The organisms 

 are furnished by the corn meal. These were purified by Kohman who 

 found that they lost their gas-producing power when preserved in or on 

 usual laboratory media, but retained their desirable properties includ- 

 ing gas production if preserved in the dry state after mixing with a 

 starchy material. The gases formed during salt rising bread fermenta- 

 tion were about two-thirds hydrogen and one-third carbon dioxide. 

 Yeast is not of importance in the rising of this bread. 



Bread is subject to a number of imperfections or diseases. Soggy 

 bread may be due to a prolonged period of rising, use of insufficient 

 yeast or poor yeast, use of too much water in proportion to the flour, 

 or too weak flour, insufficient kneading or improper baking. Ropy 

 or slimy bread is caused by spore-bearing organisms, usually B. mesen- 

 tericus vulgatus, which live through the baking process. Either the 

 yeast or the flour may be the source of infection. It is stated that 

 bread becomes stale because of the migration of moisture from the 

 crumb to the crust, leaving the crumb dry and crumbly and the crust 

 pliable and soft instead of flinty and brittle. It is also due in part to 

 the starch reverting from the semi-soluble form of the fresh loaf to its 

 original harsh form. Molds of the mucor group sometimes develop 

 quickly in a warm moist atmosphere. 



Sour bread, the most dreaded of all imperfections, is usually due to 

 the growth of butyric organisms. The clean sour flavor developed by 

 lactic bacteria is not so objectionable, and is even preferred to the 

 usual flavor of bakers' bread by many. 



Micrococcus prodigiosus may develop on moist bread after long 

 standing, with the formation of red spots. It seldom occurs, however, 

 and is not considered harmful to health. 



* H. A. Kohman. Salt Rising Bread and Some Comparisons with Bread made by Yeast. 

 Jour. Ind. and Eng. Chem., 1912, pp. 20, 100. 



