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① Yeast used too many generations, yeast aging, directly resulting in the ability to reduce diacetyl is poor, slow. Therefore, the generation of yeast should not exceed 6 ~ 8 generations.
② The low amount of yeast inoculation increased the number of new cells and the production of diacetyl. Therefore, the inoculation amount should not be too small, and it should be controlled at 0.6% ~ 0.8%.
③ The lack of dissolved oxygen content in wort hindered the reproduction of yeast, reduced the number of cells, slowed down the hypoglycemic rate and delayed the reduction of diacetyl. Therefore, the dissolved oxygen content of wort should reach 7~8 mg / L to ensure the yeast reproduction. However, too high oxygen content will promote yeast over reproduction, but will increase the production of diacetyl.
④ The content of a-amino nitrogen in wort was insufficient. Because high a-amino nitrogen content can effectively inhibit the synthesis of valine and reduce the production of a-acetolactate, the content of diacetyl will be reduced accordingly. Therefore, in order to control the formation of diacetyl, the content of a-amino nitrogen in wort should reach 180 ~ 200 mg / L.
⑤ The high temperature in the early stage of fermentation results in the excessive reproduction of yeast, which also forms a large number of metabolites diacetyl. Therefore, the lower temperature should be controlled in the early stage of main fermentation, and the temperature should be increased in the later stage to accelerate the reduction of diacetyl.
⑥ The temperature of diacetyl reduction period was lower (below 10 ℃), which did not affect the amount of diacetyl reduced, but would reduce the speed of diacetyl reduction and prolong the fermentation time.
⑦ Too high tank pressure in the early stage of fermentation inhibited the normal reproduction of yeast, so that the number of yeast in liquor was too small, the fermentation was slow in reducing sugar and diacetyl. Therefore, the micro pressure (0.01 ~ 0.02MPa) is generally adopted in the early stage of fermentation, and the pressure is gradually increased in the late stage of main fermentation, which not only limits the excessive reproduction of yeast and the generation of by-products, but also ensures the sufficient number of yeast, so that beer fermentation and diacetyl reduction can be carried out smoothly.
If there are too few yeast in liquor, the method of adding appropriate amount of high soaking liquor and increasing the temperature of diacetyl reduction period should be adopted. In addition, the yeast can be suspended in the liquor without premature precipitation by stirring with CO2, so as to improve the effect of reducing diacetyl. At the same time, some harmful volatile substances such as diacetyl can be removed by CO2.
⑧Improper cooling control makes yeast settle prematurely. Generally, the cooling in the early stage of fermentation mainly depends on the upper part of the tank, so that the temperature of the liquor is low and high, forming the convection of the fermentation liquor. The yeast is evenly suspended in the liquor, accelerating the fermentation and diacetyl reduction. If the lower cooling is turned on too early or too large to force the yeast to coagulate and settle too early, the fermentation speed and diacetyl reduction will be affected. In this case, the cooling valves of the upper and lower sections should be adjusted in time to promote the convection of fermentation liquid in the tank. In addition, CO2 can be added for proper stirring to make the settled yeast re suspend in the liquor, so that the fermentation and diacetyl reduction can be carried out smoothly.
Thanks for your reading.
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