Yeast recovery stage: the main component of yeast cell membrane is sterol. When the yeast has been propagated in the last round, the content of sterol is very low. Therefore, when the yeast is inoculated again, firstly, sterol should be synthesized to produce a new cell membrane. The recovery of permeability and the biosynthesis of reproductive sterol 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, the so-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 the sugar, and the liver sugar is accumulated again for the next inoculation.
Aerobic breathing stage: this stage mainly refers to the yeast cells with 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 following fermentation:
Main fermentation:
Appearance state and requirements of fermentation stage
1. After yeast was added to wort for 8- 16 hours during the yeast propagation period, small bubbles of carbon dioxide appeared on the liquid surface, gradually forming white, creamy foam, and the yeast immediately entered the main fermentation tank after 20 hours of propagation.
2. After returning to the tank for 4-5 hours in the foaming period, more bubbles gradually appear on the wort surface, which are white, delicate, thick and compact, like a flower, with small bubbles of carbon dioxide upwelling and some precipitates.
3. 2-3 days after high-bubble fermentation, the foam increased, forming a bulge, and gradually turned brown due to the separation of hops resin and protein-tannin complex in the wine. At this time, it is a vigorous fermentation period, which requires artificial cooling, but it should not be too intense to avoid premature precipitation of yeast and affect fermentation.
4. After 5 days' fermentation, the fermentation power gradually weakened, the carbon dioxide bubbles decreased, the foam shrank, the precipitate in the wine increased and the foam turned brown.
5. After 7-8 days of fermentation in the bubble cap formation period, the foam retracts to form a bubble cap, skimming the separated polyphenol complex, hops resin, yeast cells and other impurities, and at this time, the temperature should be greatly reduced to precipitate the yeast.
Post-fermentation and storage: the fermented liquid of wort after main fermentation is called tender beer. At this time, the carbon dioxide content of the wine is insufficient, and the volatile substances such as diacetyl, acetaldehyde and hydrogen sulfide have not been reduced to a reasonable level, so the mouth of the wine is immature and not suitable for drinking. A large number of suspended yeast and condensed substances have not yet settled down, and the liquor is not clear enough. Generally, it will take several weeks for post-fermentation and liquor storage, and the maturity and clarification of beer are in the post-fermentation and liquor storage period.
Above fermentation
The main methods of fermentation above: traditional skimming method, falling method, Barton combined method and Yorkshire method.
The upper fermentation adopts the upper fermentation yeast, and the fermentation is carried out at 15-20 degrees Celsius. The amount of cells formed is large, the yeast recovery is complicated, and the generation is far more than that of the lower fermentation yeast, and there is no decline for a long time.
The beer fermented above has the advantages of rapid maturation, rapid equipment turnover, unique flavor, but short shelf life. 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 technical 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 20 hours or so.
Maximum temperature of main fermentation: 18-20 7.5-9
Main fermentation time: 4-6 days and 7-8 days.