(1) As a starter, yeast absorbs nutrients in dough, grows and reproduces, and converts glucose in flour into water and carbon dioxide gas, which makes dough swell and soften, resulting in a honeycomb structure.

(2) Of course, there is also a premise that the dough produces enough gluten when kneading, which can wrap these carbon dioxide gases to prevent them from overflowing and keep the dough in a state of swelling and softness.

(3) Yeast must have water to survive. The optimum growth temperature is 20℃ ~ 35℃, below 0℃ or above 47℃. Generally, yeast cells cannot grow, and the optimum humidity is about 75%.

2. Factors affecting fermentation:

Temperature (1) is an important factor affecting yeast fermentation. Yeast needs a certain temperature range during dough fermentation, which is generally controlled at 25 ~ 30℃. If the temperature is too low, it will affect the fermentation speed. Excessive temperature can shorten the fermentation time, but it will create favorable conditions for the growth of miscellaneous bacteria and make the dough sour.

(2) The dosage of yeast: generally, the dosage of yeast is 0.6%- 1.5% based on flour. According to the variety of bread, the amount of yeast is different. If the effect of yeast is not good, it is necessary to increase the dosage of yeast.

(3) Flour: Flour with different maturity and gluten, or flour with inhibited amylase activity, will affect the function of yeast.

(4) Moisture: In a certain range, the higher the moisture content in the dough, the faster the yeast spores grow, and vice versa. So the softer the dough, the faster the fermentation speed.