What are the stages of beer fermentation? What are the fermentation products?

After yeast is added to the cooled wort, fermentation begins. The whole fermentation process can be divided into: yeast recovery stage, aerobic respiration stage and anaerobic respiration stage. After inoculation, the yeast began to recover its physiological activity under the condition of oxygenated wort. Amino acids in wort are the main nitrogen source and fermentable sugar is the main carbon source. They breathe and get energy from it to reproduce, and at the same time produce a series of metabolic by-products. After that, alcohol fermentation was carried out under anaerobic conditions.

Yeast recovery stage: the main component of yeast cell membrane is sterol. When the yeast is propagated in the last round, the content of sterols is very low. Therefore, when yeast is inoculated again, sterols should be synthesized first to produce new cell membranes. The recovery of permeability and biosynthesis of reproductive sterols are mainly carried out with the participation of unsaturated fatty acids and oxygen, and the main energy sources of synthesis and metabolism are provided by glycogen and trehalose in temporarily stored cells. In the second stage, yeast cells basically do not reproduce, which is called yeast stagnation period. Once the cell membrane is formed, the permeability is restored and nutrients enter, the yeast immediately absorbs the energy provided by sugar, and the liver sugar accumulates again for the next inoculation.

Aerobic breathing stage: this stage mainly refers to the yeast cells that use fermentable sugar as the main energy source and reproduce under the action of oxygen.

Anaerobic respiration stage: In this fermentation process, most fermentable sugars are decomposed into ethanol and carbon dioxide. These sugars are absorbed by yeast, and the order of glycolysis is glucose, fructose, sucrose, maltose and maltotriose.

The next fermentation:

Main fermentation:

Appearance state and requirements of fermentation stage

1. During the yeast breeding period, after adding yeast to wort for 8- 16 hours, small bubbles of carbon dioxide appeared on the liquid surface, gradually forming white creamy foam, and the yeast immediately entered the main fermentor after 20 hours of breeding.

2. After returning to the tank for 4-5 hours during the foaming period, more bubbles gradually appeared on the surface of wort, which was white, delicate, thick and dense, like a flower, with small bubbles of carbon dioxide upwelling and some sediments.

3. After 2-3 days of high-bubble fermentation, bubbles increased to form bulges, which gradually turned brown due to the separation of hops resin and protein-tannin complex in wine. At this time, it is a vigorous fermentation period, which requires artificial cooling, but it should not be too intense, so as to avoid premature precipitation of yeast and affect fermentation.

4. After 5 days of fermentation, the fermentation power gradually weakened, the carbon dioxide bubbles decreased, the foam shrank, the sediment in the wine increased, and the foam turned brown.

5. After 7-8 days of fermentation in the blister formation period, the foam shrinks to form a blister, skimming off the separated impurities such as polyphenol complex, hops resin and yeast cells. At this time, the temperature should be greatly reduced to precipitate the yeast.

Post-fermentation and storage: wort fermented liquid after main fermentation is called tender beer. At this time, the content of carbon dioxide in wine is insufficient, and the volatile substances such as diacetyl, acetaldehyde and hydrogen sulfide have not been reduced to a reasonable level, so the taste of wine is not mature enough for drinking. A large number of suspended yeast and coagulants have not yet settled down, and liquor is not clear enough. Post-fermentation and wine storage usually take several weeks, and the maturity and clarification of beer are in the post-fermentation and wine storage period.

Above fermentation

The above main fermentation methods: traditional skimming method, falling method, Barton combination method and Yorkshire method.

The upper fermentation adopts upper fermentation yeast, and the fermentation temperature is 15-20 degrees Celsius. The amount of cells formed is more, the recovery of yeast is more complicated, and the generation is far more than that of lower fermentation yeast, and it will not decline for a long time.

The fermented beer has the advantages of fast maturation, rapid equipment turnover and unique flavor, but the shelf life is short. Generally, the post-fermentation period is not used, but the glue is added. After the clarification stage, carbon dioxide is artificially charged to reach saturation.

Comparison of technological parameters between upper fermentation and lower fermentation;

The above main fermentation technical requirements and the following fermentation technical requirements

Inoculation temperature: 14- 16 5-7.

Yeast addition: 0. 15-0.30%, 0.4-0.6%.

Yeast proliferation time: 8- 16 hours and about 20 hours.

Maximum temperature of main fermentation: 18-20 7.5-9.

Main fermentation time: 4-6 days and 7-8 days.