There is a sober process before steamed bread is put on the cage. If you are fully awake, you must put it in a cage and steam it on the fire.

As the saying goes, a big fire leads to a small fire. Your situation is probably that the steamed bread is completely awake, and the fire is too small after being put into the cage. The steamed bread continued to wake up in the cage, and the air pressure in the upper cage was high and the situation was normal.

The air pressure below is very small. When the steamed bread wakes up, the skin wrinkles and the brightness decreases.