The Brewing Fermentation Stage
The brewing fermentation stage is divided into the main fermentation and post-fermentation, with a yeast recovery stage in between. The wort enters the main fermentation stage when it is put into the tank. Generally, when the wort is cooled, many precipitations will precipitate by the cold, which we call cold coagulation. Generally, it will be discharged within 12-24 hours after the tank is full. It has no direct impact on the liquor, but it will affect the taste and reduce the satisfaction of the tasting. The main fermentation period is generally based on temperature and sugar content as the main control indicators, supplemented by pressure, pH, and yeast peak indicators. During the period, the temperature should be kept constant, the temperature should be raised and lowered according to the process requirements, and the sugar content should be continuously measured (sugar measurement instruments are generally divided into specific gravity sugar meters and electronic sugar meters, the latter is relatively more expensive, but the accuracy is perfect. It is suitable for high-end brands of large-scale equipment, and a specific gravity Brix meter can be used for ordinary brewing), waiting for the process transfer point to proceed to the next step. In general, the process transition point after the main fermentation is completed is the yeast recovery stage.
Yeast Recovery Stage
Regarding the yeast recovery stage, micro-brewing beer equipment generally has two forms if there is no yeast tank. One is suspending yeast, pouring the post-fermentation fermented liquid into another fermentation tank, and the remaining yeast is directly reserved for the next production. The other is settling yeast, which directly pours the yeast into another fermenter to start the next production. Generally, fresh yeast can be stored for 72 hours without stress. After a time, the yeast’s mortality rate and infection rate will be very high, which is unsuitable for producing high-quality craft beer. The recovery stage of yeast is also a good time to improve the quality of yeast and roughly select yeast species, especially sedimentation yeast. Because yeast is layered in a fermenter, the quality of yeast in the different layers tends to vary widely.
Generally, the quality of the lowest yeast is the worst; not only the mortality rate of yeast is very high, but also impurities such as cold coagulation and some yeast autolysates and by-products. The higher the yeast, the better the quality of the yeast, but there is a problem that needs to be noted: the upper yeast’s yeast proportion is deficient. Mixed with too much wine, if the same yeast produces different varieties, the two wines will be mixed (pay attention to this for those who have higher quality control requirements).
The yeast problem is the final stage of fermentation – post-fermentation, which we call diacetyl reduction. At this stage, the yeast begins to survive anaerobically and survive by absorbing the by-products produced by the main fermentation, which is also the process of absorbing harmful substances in the fermentation broth. The main control points of post-fermentation are conventional indicators such as temperature and pressure. But there is one point that becomes particularly important in the post-fermentation period, that is, the yeast begins to autolyze at this time, and the autolysate of the yeast will endanger the quality of wine, quality control, physical and chemical indicators, etc., which can be described as harmful and harmful. No benefit. Therefore, a waste yeast discharge plan must be formulated during post-fermentation.