564 MICROBIOLOGY OF FOODS 



BREAD* 



Success in bread-making depends more upon the control of the various 

 types of fermentation organisms used in the rising of the dough than 

 upon any other step in the process. Generally, the rising of the dough, 

 to which bread owes its lightness, is caused by yeast fermentation. 

 The yeast is usually a strain of Saccharomyces cerevisice. It is normally 

 accompanied by other organisms, notably, those of the lactic group. 

 The character of the bread depends very largely upon these bacteria, 

 its quality being improved by moderate growth and injured by ex- 

 cessive growth of these accessory organisms. 



The yeast used in bread-making is produced by different methods, 

 according to the custom of the various countries or regions. In the 

 United States, compressed yeast prepared as described elsewhere in 

 this chapter is used. 



The compressed yeast is ordinarily employed in one of two general 

 ways: By the "straight off" method and as "sponge" or "batter." 

 In the former method, which is the one most commonly employed in 

 bakeries, the yeast, flour, water, salt, sugar, or sugar substitute, and 

 shortening (fat or oil) are mixed at once and permitted to rise. Milk 

 or dried milk powder is often used to replace water wholly or in part, 

 resulting in a loaf of higher nutritive value and richer flavor. In some 

 cases, proprietary yeast foods are added with the other ingredients. 



Salt is added to the dough to improve the flavor and to retard 

 diastatic and bacterial activities; if unchecked, the diastase of the 

 flour tends to soften the starch which gives a soggy loaf or too sweet a 

 flavor. 



Sugar is added to provide material for yeast fermentation little of 

 the sugar is used for multiplication of the cells for the reason that the 

 time of rising of the dough is not sufficient to permit very great increase 

 in number of the cells and the other yeast foods are not favorable to 

 rapid growth. Sugar has been replaced in practically all modern baker- 

 ies by malt syrup. Malt syrup is made by concentrating to about 80 

 Brix in large copper vacuum pans a sweet wort made by the malting 

 and mashing of barley or barley plus corn or rice grits. It is dark 

 amber in color, possesses a strong malt flavor, and usually one to three 

 per cent of lactic acid made by "souring of the mash" with pure cul- 

 tures of lactic bacteria before concentration. Malt syrup possesses 



* Prepared by W. V. Cruess. 



