Why should lard be added to steamed buns or steamed bread noodles in five-star hotels?

When eating in a five-star hotel, I feel that steamed buns or steamed buns are strong, fluffy and oily. Asked the chef and said that he added some lard. Smelling the aroma of steamed bread, the saliva has come out. However, at the moment of cooking, individual steamed buns suddenly became smaller and even shrunk into a porcelain "pimple". This is like an invisible hand pinching steamed bread, which is commonly known as "ghost pinching steamed bread" among the people. At this time, my heart is very collapsed. Have you ever been in this situation? What the hell is going on here? The shrinkage of steamed bread is due to the dense skin of steamed bread, the temperature difference between inside and outside of steamed bread is large at the moment of uncovering the pot, and the gluten skeleton can not bear the pressure of the atmosphere, thus making steamed bread shrink into a ball quickly. Besides low temperature, there are several factors that cause shrinkage. First, the operation process problems: 1. Excessive proofing of dough is generally called "old". This kind of dough is very soft and collapsed, and it becomes mushy seriously, so it won't bulge if pressed; Grasp the silk without tendons, that is, there is no bones and muscles, and some are scattered like tofu dregs; The sour taste is strong, so this kind of dough can't be used to make finished products. If it is steamed, the gluten skeleton can't play a good supporting role, and steamed bread is easy to shrink. 2. If the dough is kneaded for too long or stirred excessively, the dough will lose elasticity, the viscosity will be too high, the gluten will be destroyed, and it will not be easy to produce gluten when washed, thus the gas storage capacity of steamed bread will be reduced, causing steamed bread to shrink. 3. Steamed bread is submerged by steam for a long time in the steaming process. Practice has proved that steamed bread placed in the middle of the steamer is easy to shrink. Because the steamed bread in the middle is often dived or even dripped by the steam flowing back from the top of the steamer, the skin is sticky and too dense, which leads to shrinkage. 4. Too much water will accelerate the decomposition of protein by enzymes and weaken the elasticity and extensibility of dough, which will make the dough sticky and bring difficulties to the operation. Too fast fermentation will easily lead to rancidity, irregular shape of finished products, and even shrinkage will become inferior products.