Novices and sourdoughs often encounter the phenomenon that the dough does not rise. The temperature of the dough, the fat content, the amount of salt, etc. will affect the fermentation speed and effect. But yeast failure is a relatively common problem. So if you buy yeast for a long time, you can use the following method to test whether the flour starter is active.

　　 1. After the yeast is dissolved in warm water, wait for 5-10 minutes. If there is a lot of foam, it means it is a yeast with good activity. On the contrary, it has less foam and low activity, so it is not recommended.　　

　　2. Prepare a half cup of warm water, which is about the same temperature as your fingers. Add 1/2 teaspoon of sugar to the warm water to serve as the yeast's nourishment. Stir slowly, then add an appropriate amount of dry yeast, stir well, and let stand for observation.

　　3. If the dry yeast you buy is a large bag, it can be stored at room temperature before opening. After opening, please put it in a sealed bottle and put it in the refrigerator (5℃ is more suitable). The sooner it is used up, the better. For home use, it is recommended to buy small packages of yeast to avoid losing its activity after a long time.

　　 The above is the test method for whether the flour starter is active. If you pass the above test, the dough still can not ferment, it is caused by other reasons.