The fermentation process of top fermentation and bottom fermentation

The beer fermentation is a process by which yeast converts fermentable sugars in wort into alcohol and carbon dioxide under certain conditions. Due to the different types of yeast, fermentation conditions and flavors are also different. According to different types of yeast , beer can be divided into top fermented beer and bottom fermented beer.

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

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

The bottom fermentation:

1. Yeast propagation stage: 8-16 hours after the wort is added with yeast, small bubbles of carbon dioxide appear on the liquid surface, gradually forming white, creamy foam.

2. Foaming stage: 20 hours after yeast propagation, more foam will gradually appear on the wort surface , gradually moving from the surroundings to the middle, white and delicate, thick and dense, with small bubbles of carbon dioxide surge up and bring out some precipitates.

3. High-foaming stage: 2-3 days after fermentation, the foam will increase to form a bulge, and gradually turn brown because the hops resin and protein-tannin complex in the beer begin to precipitate. This is the period of vigorous fermentation, requiring cool down, but not too vigorously to avoid premature precipitation of yeast and affect fermentation.

4. Defoaming stage: After 5 days of fermentation, the fermenting power gradually weakens, the carbon dioxide bubbles decrease, the foam shrinks, the precipitation in the beer increases, and the foam becomes brown.

5. Bubble cover formation stage: After 7-8 days of fermentation, the foam shrinks to form a bubble cover, and stripping out precipitated polyphenol complexes, hop resins, yeast cells and other impuritiesthe . At this time, the temperature should be drastically reduced to allow the yeast to settle .

6. Post-fermentation and storage: the fermented liquid of wort after the main fermentation is called fresh beer. At this time, the carbon dioxide content of the beer is insufficient, and the volatile substances such as diacetyl, acetaldehyde and hydrogen sulfide have not been reduced to a reasonable degree. The taste of the beer is immature and not suitable for drinking. A large amount of suspended yeast and coagulated substances have not yet settled, and the beer is not clarified enough. Generally, there will be a few weeks of post-fermentation and storage period. The maturation and clarification of beer are both in the post-fermentation and storage period.

Top Fermentation

The top fermentation uses the top fermentation yeast, and the fermentation is carried out at 15-20 degrees Celsius. The quantity of cell formation is large, and the yeast recovery is more complicated. The generation number is far greater than the lower fermentation yeast, and there is no decline for a long time.

The top fermented beer matures quickly, the equipment turns quickly, and the beer has a unique flavor, but the shelf life is short. Generally, the post-fermentation period is not used. After the first stage of clarification, artificial carbon dioxide is used to achieve saturation.

Comparison of the technical parameters of the fermentation above and below:                         

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