When steaming steamed bread, it is fermented by yeast, whether it is granular or powdery, but if it is vacuum-packed, don't get wet, otherwise the effect will be bad. If the effect is not good, baking powder or baking soda can be added appropriately, which belongs to chemical leavening agent and can play the role of auxiliary puffing, but the addition amount should not be too much, otherwise the taste and taste will not be affected.

Poor fermentation can also cause collapse, which may be too late or not in place, so try more and master the degree of fermentation.

I hope you can succeed next time.