2, the old face refers to the face seeds of the hairy face, which is called a face screwdriver in the north. It's a small dough left over from steaming steamed bread, because there are many yeasts in it, which will be used as a strain next time. This kind of steamed bread made of the last fermented flour is called old flour steamed bread. In contrast, steamed bread made directly from yeast (dry noodles and fresh noodles) can't be called "old noodles". Lactic acid bacteria often exist at the same time in the preservation process of old noodles, which will have a unique sour taste after a long time, so it is necessary to add edible alkali to neutralize its sour taste when steaming steamed bread with old noodles.