Key points of the main fermentation process

Main fermentation, also known as pre fermentation, or fermentation for short, is the main stage of beer fermentation. Its main content is to ferment wort mainly composed of maltose with beer yeast to produce alcohol, CO2 and a series of other by-products to form the main components of beer. Taking the traditional low temperature fermentation of 12% wort as an example, the key points of the technology are described as follows.

• The wort was cooled to the inoculation temperature of about 6 ℃. After part of the wort flowed into the breeding tank, the required yeast (0.5% of wort) was added, and then the cooling wort was added to make it mixed evenly.

• The wort is ventilated by a special oxygenation equipment, so that the sterile air is evenly and densely dispersed in the wort. The dissolved oxygen content of wort after inoculation should reach about 8 mg / L.

• When the wort was full (the liquid level was 30cm away from the slot), the yeast entered the breeding period. After 16~20h, a white foam will form on the surface of wort. This is the way to pour the wort into the fermentation tank from the breeding tank. The dead yeast cells and protein coagulate precipitated at the bottom of the breeding tank can be separated through the pouring tank.

• The dissolved oxygen in wort was almost exhausted by yeast, and the yeast began anaerobic fermentation. After that, the temperature of fermentation broth and hypoglycemic effect should be checked regularly.

• After 2 ~ 3 days of fermentation, the temperature of fermentation broth was close to the maximum fermentation temperature, and the fermentation entered the vigorous period. During this period, the hypoglycemic rate is fast, and the apparent sugar content drops by 1.5% ~ 2.0% every day. The cooling water should be turned on appropriately (about 2 ℃), and the temperature should be controlled for 2 ~ 3 days according to the process requirements.

• After that, the cooling capacity increased gradually, the fermentation temperature decreased gradually, and the hypoglycemic rate also slowed down. The decrease of fermentation temperature should be coordinated with the hypoglycemic situation according to the process requirements, so that the temperature should be controlled at 4.0 ~ 4.5 ℃ and the sugar content should be controlled at 4.0% ~ 4.2% after the main fermentation.

• In the last day of the main fermentation, the temperature should be dropped sharply to make most of the yeast settle at the bottom of the tank, and then sent to the wine storage tank for post fermentation. Only (5 ~ 10) × 106 CFU / ml yeast cells were retained in the fermentation broth for post fermentation and diacetyl reduction.

• The precipitated middle layer yeast was recovered, screened and washed, and stored at 2 ~ 4 ℃ for the next batch of inoculation.

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