What makes steamed bread moldy is a large class of fungi-mold, a microorganism called Aspergillus. Aspergillus consists of aerial hyphae and vegetative hyphae. Look at the moldy steamed bread surface, there are often blue, brown or black spots. In fact, it is formed by gathering airborne hyphae of Aspergillus, which are used by Aspergillus to breathe. When you break the moldy steamed bread, you will see sticky silk inside. That is the nutritional mycelium of Aspergillus, which goes deep into the steamed bread to decompose sugar for mold growth. Summer is very conducive to the growth of mold because of the hot and humid weather. Therefore, food is particularly prone to mildew and deterioration in summer. Remember, moldy things are generally not edible.