In recent years, due to the continuous development of beer theory and fermentation technology, the traditional top fermentation and bottom fermentation processes have been greatly improved, and the production methods have also undergone great changes. For example: now people have used vertical fermentation tanks to produce upper fermented beer such as wheat beer, and recovered yeast from the bottom of the tank, of course, the yeast can also be recovered with a centrifuge; in order to shorten the production cycle, when producing the lower fermented beer, a relatively The high main fermentation temperature greatly shortens the time of post-fermentation, that is, post-ripening. The emergence of these new technologies not only improves the quality of beer, but also significantly improves the production efficiency of beer.
The traditional fermentation process of 12% wort at low temperature is briefly described as follows:
(1) Cool the wort to the inoculation temperature of about 6°C. After part of the wort flows into the yeast breeding pool, add the required yeast, and the amount is about 0.5% of the volume of the wort. Yeast can also be added to the cold wort in the pipeline using a dosing pump. In this way of adding yeast, the yeast and the wort are fully mixed, and the wort rises faster.
(2) The sterile air passes through the special oxygenation device, so that the oxygen is dispersed finely and fully mixed with the wort in the pipeline, so that the oxygen is evenly dispersed in the wort. Wort ventilation and wort cooling are carried out at the same time. The dissolved oxygen content of the wort after inoculation should be controlled at about 8mg/L.
(3) After adding yeast, add wort to the breeding pool until the pool is full. The wort liquid level should be 30cm away from the upper mouth of the breeding tank to prevent overflow.
(4) About 20h of yeast reproduction, a layer of white foam will form on the surface of the wort. This is to carry out the pouring operation. The fermentation liquid is pumped from the breeding tank into the fermentation tank. Through the pouring, impurities such as dead yeast cells, protein coagulation and hop resin that settle at the bottom of the breeding tank can be separated.
(5) After pouring into the pond, all the dissolved oxygen in the wort has been consumed by the yeast, and the yeast begins to anaerobic fermentation. After that, the temperature of the fermentation broth and the hypoglycemia should be checked regularly.
(6) Fermentation is about 2 to 3 days, the temperature of the fermentation broth rises to the specified relatively high fermentation temperature, and the fermentation enters a vigorous period. During this period, the sugar reduction rate is fast, the apparent sugar content drops by 1.5%~2.0% every day, and the temperature gradually rises. It is necessary to open the ice water (about 2 °C) in time, and control the temperature for 2~3 days according to the process requirements.
(7) After that, the cooling amount gradually increased, and the fermentation temperature gradually decreased. as fermentation progresses. The speed of sugar reduction is gradually slow. Generally, the brewing sugar of 12% beer is controlled at 4.0~4.2°P, and the brewing temperature is controlled at 4.0℃~4.5℃.
(8) The temperature should be sharply lowered one day after the main fermentation, so that most of the yeast settles at the bottom of the pond, and then is sent into the post-fermentation tank for post-fermentation. Only (3~4) times the sixth power of ten/ml yeast cells are retained in the fermentation broth for post-fermentation and reduction of diacetyl.
(9) Recover the precipitated yeast in the middle layer, carry out sieving and washing, and store it at a low temperature (about 2° C.), and reserve it for the next batch of inoculation. The storage time should not exceed 2 days, in order to prevent the gradual consumption of liver sugar in the yeast cells, resulting in a decrease in yeast fertility and an increase in dead yeast cells.
