Fermentation methods and processes commonly used in breweries
In order to facilitate operation and save labor, most breweries have used conical fermenters to produce beer and carry out main fermentation and post-ripening. Due to the influence of the enterprise's own conditions or production and supply objects, the processes adopted by the production enterprises are not the same. There are two aspects: one is the division of equipment, which can be divided into one tank fermentation method, two tank fermentation method and the combination of modern and traditional fermentation methods; the other is the division of temperature, which can be divided into low temperature fermentation method and high temperature fermentation method.
Tiantai mainly discusses the one-pot fermentation method and the two-pot fermentation method.
One pot method
The entire fermentation process is carried out in a conical tank, which is called "one-pot method". Most enterprises adopt two processes on the basis of one tank-low-temperature fermentation and high-temperature fermentation due to seasonal or product quality factors. The total time of low-temperature one-pot fermentation process is 23-28 days, and the total time of high-temperature one-pot fermentation process is 12-15 days.
1. Low temperature fermentation process
The low-temperature fermentation process is widely used in our country, and it is more suitable for conical tank fermentation with traditional yeast.
The hot wort was removed from the hot coagulation and hop grains through the gyratory sedimentation tank, cooled to the inoculation temperature of 6°C~8°C through a plate heat exchanger, and filled with sterile air to make the dissolved oxygen reach 7~8mg/L. Inoculate yeast (0.5%~1.0% inoculum) and then pump into the fermenter for fermentation. The filling factor of the fermenter was 0.8~0.9. After the fermentation started, the inoculation temperature was maintained for 3 days, and then the temperature was naturally raised to 10°C, and the main fermentation was carried out at this temperature.
When the apparent fermentation degree of the fermentation broth reaches 55%, raise the tank pressure to 0.07~0.1Mpa to accelerate the reduction of diacetyl and reduce the formation of higher alcohols and esters. After another 3-4 days, when the content of diacetyl drops below 0.1mg/L, start to cool down slowly to 5°C at a rate of 0.3°C/h or continue to cool down without stopping. If it stays at 5°C, keep it at this temperature for 24 hours, discharge or recover the yeast, and then cool down to 0°C~-1°C at a rate of 01°C/h. Store at this temperature for 10-15 days. Drain the yeast and cold solids the day before filtering the wine. The liquor can be filtered through a centrifuge to separate the yeast, or it can be filtered directly.
2. High temperature fermentation process
A number of domestic breweries have brewed beer using high-temperature (14°C-17°C) fermentation processes. The long fermentation period is 18-21 days, and the short one only needs 12-15 days, the utilization rate of equipment is significantly improved, and the production cost is greatly reduced.
After the hot wort is removed from the hot coagulation and hop grains by the gyratory sedimentation tank, it is cooled to 9.5 ℃ ~ 10 ℃ by the plate heat exchanger, and the condensed solid is removed by flotation, and the dissolved oxygen reaches 7 ~ 8mg/L at the same time by filling sterile air. The concentration of the original wort is 12°P, and 0.6%~0.8% of mud yeast is added. The wort was kept at 10°C-11°C in the fermenter for 36 hours to proliferate the yeast, and then the temperature was raised to 12°C to enter the main fermentation. After about 2 days of fermentation, when the apparent concentration dropped to 6P, the tank pressure was increased to 0.08~0.1MPa, and the temperature was gradually raised to 16°C to continue fermentation and reduce diacetyl. About the 5th day after the tank is full, the apparent sugar content drops to the lowest point (2.~2.5°P); about the 7th to 9th day after the tank is full, the content of diacetyl can drop to below 0.1mg/L. At this time, the temperature can be slowly lowered until 0°C, after ripening and saturated with CO2, the time is 4 to 5 days. On the second day when the temperature was lowered to 0°C, discharge the yeast and recover the yeast and condensed matter one day before the wine filtration.
Advantages: simple operation; temperature, pressure and liquid level can be easily and automatically controlled; yeast recovery is also more convenient; and one-can production of beer can save the need for two-can pouring operations, reducing the chance of contact with air, less cleaning consumption, and low wine damage.
Disadvantages: Due to the strong convection of the wine, many impurities that should be separated cannot be discharged and dissolved in the wine. Therefore, the taste of beer brewed by the one-can method is rougher than that of the two-can method, the hop
bitterness is slightly stiff, and the after-bitterness is more obvious. Because the fermentation space needs to be reserved, the utilization rate of the fermentation tank is not high.
2. Two pot method
The pre-(main) fermentation and post-fermentation are carried out in the main fermentation tank and the rear storage tank respectively, so it is called "two tank method". The total cycle time of the two-pot process is about 23 days.
The wort is cooled to 5 ℃ ~ 8 ℃ and enters the conical fermenter, oxygenated and added with yeast, the amount of yeast added is 0.6% ~ 0.8%. When the appearance fermentation degree reaches 50%~55%, the cans are sealed, and the pressure is controlled at 0.07~0.1MPa. When the appearance fermentation degree reaches 60% (brix content 3.8~4.0°P), the cooling is turned off, and the wine temperature is naturally raised to 12°C for diacetyl reduction. After 3-4 days, when the fermentation degree reaches about 65%, the diacetyl content can be reduced to less than 0.1mg/L. At this time, turn on the ice water for cooling, cool down to 5°C at a rate of 0.3°C/h, keep at this temperature for 12-24h, and discharge the yeast. Then carry out the operation of pouring the tank, that is, pour the main fermentation liquid into the conical wine storage tank with a back pressure of 0.06-0.08 MPa. After pouring the cans, the beer is cooled to 0°C-1°C at a rate of 0.1°C/h in the rear storage tank. Store at this temperature for 7-10 days to make the wine fully mature. The day before filtering wine, adjust the pressure to 0.05~0.06MPa. Remove the yeast and sediment in the tank before filtering.
Advantages: The utilization rate of the fermentation tank is relatively high; the number of yeast in the post-fermentation tank is not much, after the post-storage, the yeast precipitation is more complete, the wine is clearer, and the filtration performance is good, even if there is no centrifugation, it can be filtered smoothly.
Disadvantages: Oxygen is easy to be absorbed when pouring cans, and the operation must be very careful, otherwise it will affect the quality of beer.
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