The Pressure Control for Conical Fermenters
When utilizing conical tanks for fermentation, there is no pressure at the beginning to prevent the emission of volatile substances that lead to bad taste. To recycle CO2, a slight pressure (lower than 0.01-0.02MPA) is adopted. In the later stages of fermentation, when the fermentation level reaches around 70%, the tanks are closed. The pressure is gradually increased to 0.08MPA to allow CO2 to saturate into the beer. Increasing the pressure too early can result in faster yeast settlement and is not beneficial for diacetyl reduction.
Pressurized fermentation is often accompanied by high temperature fermentation. While high temperature fermentation (above 13℃) can speed up the fermentation process, it also leads to strong yeast proliferation and excessive production of metabolic byproducts, which negatively impact beer quality. Pressurized measures during high temperature fermentation can help mitigate these issues. Controlling the duration of pressurization is crucial. If pressurization occurs too early, yeast proliferation will be inhibited, affecting the fermentation speed. If it happens too late, it will increase the production of byproducts. Therefore, it is advisable to gradually increase the pressure in sections. Yeast inoculation should be done without pressure, with the temperature controlled at 10-12℃. As the fermentation level reaches 25%-30%, the pressure should be gradually increased to approximately 0.03MPA. Subsequently, the fermenting temperature can be increased to 16℃, with the pressure also increasing to 0.16MPA.
What Causes Negative Pressure in Fermenters?
Many breweries nowadays prefer using hot water for cleaning or steam for sterilizing fermentation tanks, but this practice can be very dangerous.
Under normal pressure, the weight of 1 cubic meter of steam is 560g, while the weight of 1 cubic meter of water is 1 ton. When steam condenses, its volume reduces to 1/1786th of its original volume. This reduction can cause negative pressure and make the tanks hazardous.
In addition, negative pressure can occur if the discharge speed is much faster than the air inflow speed or when fermentation tanks are washed with hot caustic liquid, causing the absorption of CO2 by the liquid and resulting in volume shrinkage. Similarly, washing the tanks with cold water immediately after showering them with hot liquid can also lead to negative pressure. Therefore, it is recommended to keep the temperature for cleaning fermenters below 40℃.