TRANSACTIONS OF WAGNER 



92 



THE CHEMISTRY OF BREAD-MAKING 



fermentations result in the production of larger amounts than usual of certain 

 by-products of yeast action, such as glycerol, succinic acid and some of the higher 

 alcohols, such as amylic, to which bread that has been leavened with yeast 

 may owe its distinctive flavor. The optimum or most favorable temperature 

 at which yeast works ranges from 86° to 89° F. (about 30° to 32° C.)- Marked 

 deviations from this temperature bring about changes in which the quahty and 

 flavor of the bread are appreciably altered. Through carelessness in respect to 

 the temperature, other fermentations, such as the acetic or lactic, may develop 

 and the resulting product be ruined. For many centuries much yeast-leavened 

 bread was made empirically by developing home-made cultures of wild yeasts 

 by spontaneous inoculation and generation in starchy culture-media, par- 

 ticularly the potato, to which reference has been made above. Sometimes 

 instead of exposing to accidental infection from the air, these culture-media 

 were inoculated from previous cultures left over or borrowed. Such empiric 

 and irregular methods were not conducive to uniformity in the resulting bread, 

 and bread-baking has progressed more during the few years since commercial 

 yeasts are available than it did for centuries previously. The commercial 

 yeasts are usually sold in the compressed form, made by growing carefully 

 selected strains of pure yeast in properly made nutrient media and subsequently 

 removing the excess of moisture and mixing with a certain proportion of starch 

 which acts as an absorbent. 



When alcohol is the desired object of the fermentation, large amounts of 

 sugar are needed during the process. As in the case of bread-making, it is the 

 carbon dioxid that is sought, and as a gram of sugar is capable of yielding 8.2 

 c.c. of carbon dioxid, it is a fact that the sugar naturally present in wheat flour, 

 while present only to the extent of from i to 1.5 per cent., is amply sufficient 

 to supply the yeast for the maximum leavening effect desired. It is usually the 

 practice, however, to add a little sugar, which has the effect of hastening the 

 operation. Even if no sugar is added during the making of the bread, the 

 dough usually shows a higher proportion of sugar after fermentation than 

 before, notwithstanding the use of it by the yeast. This is due to the fact that 

 when water is added to flour it develops the enzymic reaction of the flour and 

 some of these naturally occurring enzyms are capable of transforming a small 

 proportion of the starch in the flour into soluble carbohydrates or sugars. 



During fermentation there is a loss of from one to three per cent, of the 

 total protein of the flour used by the yeast as food. The acidity of bread, 



