What does it mean to be a cook in the Qin Dynasty? What does it mean to give the chef only egg yolk, no protein and no water?

In the Qin dynasty, "cook" means cook, which is a title for cook. The question of "only giving the cook egg yolk, no protein and no water" may refer to a story or legend, not the reality of the Qin Dynasty. In some legends, chefs may be described as eating only egg yolks instead of protein, because egg yolks are usually more nutritious than protein. But this is not a historical fact.