I interviewed a number of steamed bun shops, and the answer I got was that the lower layer cooked first, and the steamed bun shop went down to the top of the cage first, because the steamed buns were not steamed at the same time, and the top of the cage was pushed up layer by layer, and the upper layer steamed for a long time. Then I did a lot of experiments, measured the temperature change of each layer separately, and got the conclusion that the lower layer ripened first through record analysis.

The analysis is as follows:

At the beginning, the temperature of the lower layer of the cage was obviously higher than that of the upper layer. Some steam met with the liquefaction and heat release of the lower layer of cold steamed bread, and the endothermic temperature of steamed bread increased. Only a small amount of steam rose to the upper layer, and the temperature of the upper layer of steamed bread rose slowly. When the temperature of the lower steamed bread is close to the temperature of steam, the upper steam will increase and the temperature of the upper steamed bread will gradually increase. In the later period, the upper and lower floors are all steam, and the temperature difference is not big, because all steamed bread is surrounded by steam, and steamed bread absorbs heat almost. Because the steamed bread below first encounters high-temperature steam, the temperature rises first, so the steamed bread below is cooked first.