Prepare a basin, put in about a catty of flour, and then add the prepared warm water, the temperature of which is about 40 degrees. When adding warm water to the flour, stir the flour with chopsticks until the flour looks like cotton wool, so don't add water.

Then knead the dough by hand and knead the flour into dough. After kneading the dough, you need to prepare a clean towel to cover it tightly, and then ferment the dough at a temperature of about 30 degrees. The fermentation time is preferably greater than 10 hour.

When the dough has obvious expansion and a large number of honeycombs appear, it proves that the dough has been fermented, so the fermented dough is old yeast noodles.

Cooked steamed bread fermentation

Using the method of cooked steamed bread fermentation, it is necessary to prepare three steamed buns steamed with old yeast in advance, and then break them into small pieces for later use.

At the same time, prepare a washbasin, add the required flour into it, and add warm water to stir it into cotton wool. Then, add the prepared steamed bread pieces to the flour, knead it, knead the flour into dough, and finally cover it with a clean towel (it is best to cover it with plastic wrap in winter).

Put the dough at a temperature higher than 30 degrees, and when it is fermented to twice its original size, the old yeast is ready.