After adding yeast to the cooled wort, fermentation begins. Yeast starts respiring in oxygenated conditions, using amino acids in the wort as a nitrogen source and fermentable sugars as the main carbon source. It obtains energy from this process to grow and then carries out alcohol fermentation under anaerobic conditions. The entire beer fermentation process is complex.
Changes in Chromaticity
During fermentation, the color of the wort decreases.
This decrease occurs because the pH value changes, causing the pigment material originally dissolved in the wort to condense again and form a foam cover with protein, hop resin, and other substances.
Another reason is the reduction of tannins by yeast. The extent of wort chroma reduction depends on the original wort color. High chroma wort has a larger reduction range, while low chroma wort has a smaller reduction range.
Changes in Carbonation
During the fermentation process, a significant amount of carbon dioxide is produced. Part of it dissolves in the beer while the rest escapes into the air. The solubility of carbon dioxide in beer depends on temperature and tank pressure. Beer fermented at low temperatures in closed and pressurized tanks has a higher carbon dioxide content, while beer fermented at high temperatures in open tanks has a lower carbon dioxide content.
Changes in Bitterness
During fermentation, nearly 1/3 of the bitter substances in the wort are lost. Factors influencing this loss include wort ventilation volume, pH value, fermentation time, yeast species, yeast addition, fermentation foam cover, fermentation temperature, fermentation pressure, and fermentation container.
Formation of Calcium Oxalate
Oxalic acid is an intermediate product of sugar metabolism. During fermentation, calcium oxalate precipitates from the liquor and attaches to the yeast and fermentation container in the form of crystals. It is the main component of “beer stone”.
Currently, the most commonly used fermentation equipment worldwide is the cylindrical-conical fermentation tank. It is airtight, clean, hygienic, and equipped with cooling facilities. It facilitates yeast discharge and effectively ensures beer quality.
Due to the static pressure of the liquid, carbon dioxide in the beer forms a gradient that distributes unevenly. The lower layer of beer has a high carbon dioxide content and low density, while the upper layer has a low carbon dioxide content and high density. This convective movement from bottom to top stirs the beer, promotes uniform mixing, and facilitates heat conduction. The higher the liquid level, the greater the carbon dioxide gradient and convection. Additionally, due to beer liquid convection, yeast remains suspended for a long time, making it difficult for even well-aggregated bacteria to settle quickly.
Although microbrewery conical fermentation tanks are mostly installed indoors, insulation work should be done to reduce production consumption. Typically, insulation materials such as polyurethane and polystyrene foam with a thickness of about 100mm are used.
The cylindrical conical tank is a sealed tank and must withstand a pressure of 0.1~0.3MPa. The head and cone bottom parts of the fermenter are under higher pressure compared to the lower and upper parts of the cylinder. Therefore, when designing a cylindrical conical tank, a safety valve should be installed according to the working pressure requirements.
Advantages of Cylindrical Conical Tanks
- The cylindrical conical tank is tall, allowing for the formation of a carbon dioxide gradient from top to bottom. This enables bottom-up or top-down convection in the fermentation liquid. The higher the tank, the greater the convection speed, resulting in better carbon dioxide dissolution and fine, smooth beer foam.
- The cylindrical conical tank is suitable for both bottom and top fermentation.
- It enables automated cleaning, ensuring thorough sterilization and reducing the risk of contamination by miscellaneous bacteria. This not only saves costs but also reduces labor intensity.
- Since the cylindrical conical tank is pressurized and sealed during fermentation, the loss of hop bitterness is reduced, allowing for a 15% reduction in hop usage.
- The washing process involves using a spray head with washing liquid installed at the top of the tank. The reaction force of the washing liquid spray promotes the flushing of the inner wall of the tank. To clean the tank, remove all removable accessories before cleaning and sterilize them separately.
Hygiene of the Process
- All hoses used for conveying materials must be sterilized with steam for 30-40 minutes before use. Connection ports should be sterilized with alcohol cotton. After use, rinse the residues in the pipes with water for reuse.
- The fermentation tank must be brushed and sterilized after each use.
- Maintain clean and hygienic floors and walls to prevent bacterial growth.
- No Escherichia coli should be detected in wort and fermentation broth.
Detection of Fermentation Broth
- Foam Shape: For light beer, the foam should be white, smooth, and have a lasting tear.
- Aroma and Taste: Light beer should have a noticeable hop aroma, pure taste, refreshing and harmonious beer body, soft texture, and no odor or off-flavor. Stout and dark beers should have a distinct malt aroma, pure taste, refreshing and mellow character, soft texture, strong flavor, and no peculiar smell.
- Beer Chroma: The depth of the beer’s color, mainly determined by the malting process but also influenced by the mashing and fermentation processes. It is one of the routine testing items for beer.
- Alcohol Content and Original Wort Concentration.
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