Why is steamed bread a little sour?

1. One kind of sour steamed bread has a long fermentation time, which will lead to sour steamed bread. This kind of sour steamed bread is safe to eat, because the main component of yeast is protein, and protein accounts for almost half of the dry matter of yeast.

2. Because the steamed bread is polluted by mold and bacteria, it is sour and deteriorated, and the nutrients in it are decomposed into substances with very small molecular weight, and finally into peptides and organic acids. At this time, the substance will have ammonia odor and sour taste, the food will lose its original toughness and elasticity, the color will be abnormal, and the surface will appear moldy patches.