1. Prepare 90 grams of water, 200 grams of flour, and 50 grams of old dough.
2. Knead it into a smooth dough, cover it with wrung out wet gauze, and let it sit overnight (more than eight hours).
3. The fermented dough smells sour.
4. Add 50 sugar and knead the dough.
5. Put a small amount of baking soda as shown in the picture, and knead it (three small pinches). There is no sourness anymore. (If it smells sour, add a little baking soda).
6. It's very sticky, so put an appropriate amount of flour and knead the dough.
7. Divide into six equal parts. The flour can wrap the small dough and make a round.
8. Put it in the oiled steamer. Put the steamer into 50 degree warm water and let it stand for 50 minutes.
9. Turn on high heat, steam for 20 minutes, stuffing for 5 minutes.
10. Began to eat.
