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1. Traditional beer fermentation process

(1) Main fermentation Also known as pre-fermentation, is the main stage of fermentation, is also the yeast activity period, the vast majority of fermentable sugars in the wort in this period of fermentation, some of the main metabolites of the yeast is also produced in this period. Fermentation methods are divided into two categories, namely, the top fermentation method and the bottom fermentation method. The latter method is mainly used in China. The following focuses on the following beer fermentation method.

After the addition of hops, the clarified juice is cooled to 6.5-8.0 ℃, inoculated with yeast, and the main fermentation officially begins. The yeast ferments the maltose-based wort to produce ethanol and CO2, which are the main biochemical reactions of fermentation. The main steps are as follows:

①Add yeast by direct addition method Mix the recovered yeast with the wort in the required amount (about 1:1) in a closed yeast adder, and send it into the addition tank with compressed air or a pump, and ventilate the tank appropriately for a few minutes.

②Yeast additions The amount of yeast added is often calculated according to the mud yeast on the wort volume percentage, generally 0.5% to 0.65%, usually inoculated cell concentration of 8 million to 12 million / ml. The amount of inoculation should be adjusted according to the freshness of the yeast, the consistency of the yeast, yeast using generations, fermentation temperature, wort concentration and add methods. If the wort concentration is high, the number of yeast generations used is high, the inoculation temperature and yeast concentration is low, the inoculation amount should be slightly larger, and vice versa is less.

③Fermentation first stage is also known as the low bubble period. After 15 to 20 hours after inoculation, white foam appears around the pool and expands to the center until the whole liquid surface, which is the beginning of fermentation. Then the foam gradually thickened, this stage maintained 2.5 ~ 3 days, the temperature rose 0.9 ~ 1 ℃ per day, the sugar level fell 1 ° Bx every 24 hours on average.

④ Fermentation second stage is also known as the high foam period. It is the most vigorous period of fermentation, and the foam is especially thick and can be as high as 25-30cm. due to the oxidation of the hop resin in the wort, the foam gradually turns brownish-yellow. The sugar is reduced by 1 to 1.5% per day for 2 to 3 days.

⑤The third stage of fermentation is also called the foaming period. After the high foam period, the yeast proliferation stops, the temperature starts to drop, the sugar drop rate slows down, the foam color deepens and gradually forms a foam cover composed of foam, proteins and polyphenol oxides, etc., with a thickness of 2-5 cm. 2 days in this stage, the sugar drop rate is 0.5% to 0.8% per day. When the sugar level of 12-degree wine drops to 3.8～4°Bx, the wine can be placed into the post-fermentation.

(2) post-fermentation

Post-fermentation, also known as wine storage, the purpose of which is to complete the final fermentation of residual sugar, increase the stability of the beer, full of CO2, full precipitation of proteins, clarification of the liquid; removal of bis-acetyl, aldehydes and H2S, such as tender wine flavor, and to promote the ripening; as far as possible, to make the liquor in a reduced state, reduce the oxygen content. The following beer fermentation method of post-fermentation is described below.

①The next wine The main fermentation tender wine will be sent to the post-fermentation tank is called the next wine. Under the wine, should avoid excessive oxygen intake, for this reason, the first tank will be filled with aseptic water, in the use of CO2 will be the top of the aseptic water, when the CO2 is full of wine from the bottom of the barrel into the wine. In addition, it is required to try to fill the tank as much as possible at one time, leaving a gap of 10-15cm to prevent air from entering the wine. If the liquor is saturated with CO2, oxygen is difficult to dissolve in the liquor due to CO2 overflow. Otherwise, the presence of too much dissolved oxygen in the beer is easy to cause oxidative turbidity, and produce oxidative flavor.

②Management

After the next wine, the first open fermentation to prevent too much CO2, wine foam gushing out, 2 to 3 days after the closure of the tank. The room temperature at the beginning of the wine 2.8 ~ 3.2 ℃, if the wine is exported, after a month gradually reduced to 0 ~ 1 ℃. The purpose of lowering the temperature is to ferment the residual sugar first and then clarify the wine. Note that you can't store wine of different ages *** in one room, otherwise the temperature requirements are contradictory and you can't control the room temperature.

Generally, the storage time for old craft 12°Bx wine for export is 60 to 90 days, and 35 to 40 days for domestic wine.

During the storage period, a beaker is used to take samples for observation, and usually the yeast in the tank sinks in 7 to 14 days. If the wine is unclear for a long time, it should be examined microscopically. If the yeast is suspended, it is poor yeast cohesion; if it is bacterial turbidity, it is bacterial contamination, usually can not be saved, can only be discharged; if it is colloidal turbidity, the cause is poor malt solubility, poor saccharification protein decomposition, boiling intensity is not enough, cold condensate separation and other factors caused by poor.