BREAD 277 



24 per cent, less moisture than outside air surrounding the bake- 

 houses ; and (3) that it contained at least four times more bacteria 

 than surrounding street air, and three times more bacteria than the 

 air of a typical above-ground bakehouse.* (See also p. 86.) 



The normal fermentation of bread with which all bakers are 

 familiar is due to the energy of the yeast plant growing in the 

 dough. Any other fermentation going on at the same time as the 

 normal one, or arising after the bread has left the oven, must be 

 looked upon as abnormal. 



Flour or dough is open to infection by bacteria, and scrupulous 

 cleanliness is absolutely necessary to avoid unfavourable fermenta- 

 tions. Bacteria are especially numerous in low-grade flours ; in fact, 

 the poorer the flour the larger the number of injurious organisms. 

 Prescott has lately shown that flour may contain bacilli indistinguish- 

 able from the B. coli. This organism is more liable to be found 

 in poor than in high-class flours. 



1. Sour Bread. — The commonest abnormal fermentation of bread 

 produces what is known as "sour bread," which means that the 

 odour and flavour of the bread are " sour " to the senses of smell and 

 taste. Lactic and butyric germs are commonly found in poor flours, 

 where they remain in a dormant condition until provided with the 

 essentials necessary for their growth — moisture, a sufiicient tempera- 

 ture, and proper and adequate food supply. The food supply 

 naturally surrounds them, and when water is added to the flour, 

 and the temperature is raised to between 70° and 90° F., they are 

 able to reproduce and rapidly manifest their presence by the products 

 they form. Dough, with considerable moisture present, or, as it is 

 termed, " slack," gives bacteria a better environment, and consequently 

 sourness is more apt to increase rapidly in such doughs. 



Acid-producing germs are also present in many samples of 

 yeast. Analyses of a large number of yeast samples used for 

 bread-making purposes, have shown that many of them contain 

 injurious bacteria which may lessen the alcoholic fermentation. 

 If, on the other hand, the normal alcoholic fermentation is at 

 first vigorous, and then diminishes, it gives bacteria opportunity to 

 grow. Hence, overproved dough is especially liable to become sour. 

 Dirty utensils, tubs or troughs, harbour injurious bacteria which are 

 able to reproduce when given favourable conditions. All cracks and 

 crevices which harbour food are teeming with life, usually undesirable 

 from the bakers' standpoint, and, therefore, absolute cleanliness 

 should be the rule in every detail. 



Acetic bacteria, which are often present in flours, sometimes 

 cause trouble, and as these bacteria require a plentiful supply of 

 oxygen, it has been suggested that all dough should be kept as much 

 * Special Report on Bakehouses in Finsbury, 1902. 



