Several Concepts of Beer Fermentation

Fermentation process is really fantastic and complicated process. To get a wonderful beer via beer fermenter, it is necessary to research and learn this process first.

Cohesiveness of yeast

The cohesiveness of yeast is one of its physiological characteristics. Each yeast species has a certain degree of cohesiveness. Different cohesiveness, the sedimentation speed of yeast in wine liquor is different, and the degree of fermentation is also different.

The yeast of strong cohesiveness settle early and fast, so the number of yeast cells in the beer is small, the fermentation is slow, and the fermentation degree is low; Yeast with poor cohesiveness sediment late and slow. More yeast left in the beer. Fermentation is faster, fermentation degree is higher, but low recovery, difficult to filter, which bring inconvenience to production.

In addition to being controlled by its own genes, the yeast's cohesive nature is also effected much by the environment in which it lives.

Fermentation-stop

The 'fermentation-stop' is called "no hypoglycemic".

The reasons for this phenomenon are:

• malt nutrition is not enough, oligosaccharide content is too high, α-amino nitrogen is insufficient, acidity is too high or too low;

• yeast cohesiveness is strong, causing early flocculation and sedimentation;

• yeast degeneration, mutation causes no Hypoglycemic;

• yeast spontaneous mutation, resulting in respiratory deficient.

Solution

• If it is caused by strong cohesiveness of yeast, which lead to early flocculation and sedimentation. It can be solved via increasing the amount of wort ventilation, adjusting fermentation temperature, decreasing the fermentation temperaure when the brix is near the final fermentation degree to prolong the fermentation high temperature period.

• If it is due to yeast degradation and that mutations lead to no hypoglycemic. It can be solved by replacing the new yeast species.

• If it is caused by spontaneous mutation of yeast that produces respiratory-deficient yeast. The strain can be re-cultured or replaced from the original strain.

In addition, in the preparation process of wort, it is necessary to strengthen the hydrolysis of protein, appropriately reduce the decomposition temperature of protein, and prolong the decomposition time of protein; in saccharification, saccharification temperature should be properly adjusted---Strengthening the hydrolysis in the low temperature section, ensuring sufficient saccharification time, asjuting the pH of the mash.

Fermentation degree

Fermentation degree describes the extent that fermentable sugars are converted to alcohol and carbon dioxide by yeast, reflecting changes of fermentable sugar concentrations. The fermentation degree is divided into appearance fermentation degree and real fermentation degree.

• Appearance gravity refers to the direct determination of the sugar concentration in the fermentation or beer using a saccharometer.

• The real gravity is the concentration measured after the alcohol is distilled from the fermentation liquid.

Appearance fermentation degree is generally about 20% higher than the real fermentation degree, which can be roughly converted by the following formula:

Real fermentation degree = appearance fermentation degree × 0.819

Yeast sedimentation difficulty and yeast autolysis

When the temperature difference between the lower level and the middle level of beer is 1.5 to 5 °C, it may cause yeast sedimentation difficulty and yeast autolysis. If the temperature of the yeast at bottom of the tank is too high or the maintenance time is too long, the yeast will be also autolyzed and produce yeast flavor in the beer. Sometimes the beer will be turbid after sterilization.

Solution

Check whether the meter is normal; discharge the yeast sludge in time; keep the temperature of the refrigerant at -4 °C, and at storage period, keep the temperature of the upper, middle and lower level of the beer between -1 and 1 °C.

"Tumbling" phenomenon

The "tumbling" phenomenon happened in fermentation tank will cause beer slow clarification, difficult filtration, poor quality.

It is mainly due to the improper opening of the cooling jacket, the upper temperature and the process curve deviate by 1.5 to 4 ° C, and the temperature in the middle of the tank is higher, causing strong convection of the fermentation liquid. In addition , the pressure is unstable, and the sharp rise and fall will also cause the tumbling.

Primary fermentation

The concept of primary fermentation is mainly directed to bottom-fermented beer. The main fermentation is mainly divided into the following stages:

• Yeast breeding period: After 8-16 hours of adding yeast to the wort, small bubbles of carbon dioxide appear on the liquid surface, gradually forming a white, creamy foam. The yeast enters the main fermentation tank immediately after 20 hours of breeding .

• The foaming period: after 4-5 hours of trough, more foam gradually appeared on the surface of the wort, gradually from the surrounding to the middle, it is white and delicate, thick and tight, like cauliflower-shape, with small bubbles of carbon dioxide, and brings out some precipitates.

• High foaming period: 2-3 days after fermentation, the foam is increased, forming a bulge, and gradually turns brown color due to the beginning of precipitation of the hop resin and protein-tannin complex in the beer. At this time, it is a vigorous period of fermentation, requiring labor. Cool down, but not too intense, so as to prevent too early sedimentation of yeast that affect fermentation.

• Foaming dropping period: After 5 days of fermentation, the fermenting power is gradually weakened, the carbon dioxide bubbles are reduced, the foam is retracted, the precipitates in the beer are increased, and the foam becomes brown.

• Bubble cap formation period: after 7-8 days of fermentation, the foam retracts, forming a bubble cap, removing the precipitated polyphenol complex, hop resin, yeast cells and other impurities. At this time the temperature should be drastically cooled, so that yeast precipitation.

Second-fermentation and storage

Second-fermentation and storage are also mainly directed to bottom-fermented beer.

The fermentation liquid after the main fermentation of wort is called tender beer/green beer. At this time, the carbon dioxide content of the beer is insufficient, and the volatile substances such as diacetyl, acetaldehyde and hydrogen sulfide are not reduced to a reasonable degree , and the taste of the beer is not mature and is not suitable for drinking. A large amount of suspended yeast and coagulated matter have not yet settled, the liquor is not clear enough, and it usually takes several weeks to ferment and store the beer .