Steamed buns occasionally shrink, and the regularity is not strong. Sometimes we don't meet once every few months, and sometimes two or three steamed buns shrink into one.
Generally speaking, the proportion of steamed bread shrinkage is relatively high in the following situations:
First, gluten-bitten steamed bread made of flour with strong gluten and good quality;
Second, the skin of steamed bread is smooth and dense, and the internal structure is exquisite;
Third, in spring and autumn, especially when the temperature difference changes greatly in alternate seasons.
After long-term research, we found that the shrinkage of steamed bread is a physical phenomenon, and the main reasons that affect the shrinkage of steamed bread are the strength of flour itself and the pressure difference inside and outside steamed bread. We know that the dough produces carbon dioxide gas through yeast fermentation, and many small holes are formed inside, and the steamed dough expands further to make steamed bread. The air-holding capacity of dough is closely related to the quality of gluten and the amount of water added. The better the quality of gluten, the easier it is to hold gas.
If the quality of flour is poor, the strength of gluten is weak, and the radius of internal small holes is large, it is easy to break and form large holes, so there is less gas trapped in steamed bread; However, the steamed bread with good flour quality and strong gluten has a small probability of small pores in the expansion process, and the skin is dense and airtight.
After steaming, open the lid, the temperature suddenly drops below 100℃, and the steam in the steamed bread condenses rapidly, resulting in a rapid drop in the internal pressure of steamed bread, while the external pressure is still 1 atmospheric pressure. If the internal and external pressure of steamed bread cannot be quickly balanced, then steamed bread will be compressed by atmospheric pressure, and its volume will become smaller, or even completely crushed into a dead surface.
Due to the excessive expansion of steamed bread made of weak gluten flour during fermentation, the internal structure of steamed bread is rough, small holes are broken, and there are many cracks in the skin, which is easy to form a channel connecting the inside and the outside. During the cooling process, with the condensation of steam, the internal pressure of steamed bread drops, and the external air can easily supplement the internal pressure from the cracks in the steamed bread skin to 1 atmospheric pressure, so that the internal and external pressures keep balance and are not easy to shrink.
When the tendon is stressed strongly, the skin is smooth and dense, the internal pores are uniform and not easy to break, and there are few surface cracks, so the probability of communication between the internal and external channels is small, and steamed bread is easy to block when contracting. Sometimes the internal and external air pressure can't be connected, and the steamed bread shrinks partially or completely under the pressure of external air pressure. This is also the reason why steamed bread shrinks easily when the temperature difference between the four seasons changes greatly.