You don't have to put yeast to make steamed bread, but steamed bread made with yeast will be more delicious. Yeast is a leavening agent which plays a fermentation role through the growth, reproduction and decomposition of yeast. It plays a fluffy role in the step of dough making in the process of making steamed bread, making the steamed bread fluffy.

So other food leavening agents can also be used to make steamed bread. For example, baking powder, a compound leavening agent, can also play a good role in leavening and can make dough in a short time, so the yeast in steamed bread can be replaced by other leavening agents.