Expansion culture must ensure two points: ①The original strain must have good properties; ②The yeast that is expanded must be strong and pollution-free. In the laboratory stage of expansion, due to the use of aseptic operations, as long as the operation technology and process regulations can be followed, contamination by bacteria is rarely seen. After entering the workshop, if the sanitary conditions are not well controlled, bacteria infection will often occur. Therefore, the expansion personnel must first have a strong sense of sterility. All the pipelines and valves that pass through the inoculation and wort addition process must be completely wiped out with hot water or steam. Bacteria, indoor air, floors, and walls should also be regularly disinfected or sterilized. The compressed air used for ventilation and oxygen must also be filtered by a 0.2μm membrane before it can be used. At the same time, the amount of oxygenation should be appropriate. Insufficient oxygenation will cause slow growth of yeast. Excessive oxygenation will result in too strong yeast cell respiration enzyme activity. Excessive yeast reproduction will be detrimental to the later fermentation. Generally, the propagating yeast should be oxygenated three times a day before entering the culture tank, each time for 20 minutes. The culture after fermentation requires about 9 mg/L of dissolved oxygen in the wort. Finally, each batch of expansion should also be tested for the yeast's fermentation degree, fermentability, peak diacetyl, death temperature and other indicators, so as to timely and correctly grasp whether there are new changes in the various characteristics of the yeast during use. (3) Addition of yeast: the cooling temperature of the wort before adding yeast is very important. The cooling temperature of each batch of wort must be increased in a stepwise manner. The temperature of the full tank is controlled between 7.5℃ and 7.8℃. It is strictly forbidden to have the phenomenon of first high and then low, otherwise it will be unfavorable to yeast vitality and subsequent diacetyl reduction Influence. At the same time, it is necessary to accurately control the amount of yeast added. If the added amount is too small, the growth of yeast will be slow, which is not good for inhibiting bacteria. Once infected, both taste and diacetyl reduction will be affected. If the added amount is too small, it will produce more by-products such as higher alcohols due to the excessive value of the yeast; if the added amount is too large, the yeast is easy to age, autolyze, etc., and the added amount is controlled at about 7‰. (4) Temperature control: In the fermentation process, temperature control is very critical. According to the characteristics of the bacteria, low-temperature fermentation and high-temperature reduction are used. It not only helps to maintain the excellent properties of yeast, but also reduces the generation of harmful by-products, ensuring that the taste of the wine is relatively pure and refreshing. If the fermentation temperature is too high, although the fermentation cycle can be shortened and the reduction of diacetyl can be accelerated, the too high fermentation temperature will make the beer taste more indifferent, increase the aldol by-products, and accelerate the mutation and degradation of the bacteria.