Brewing Process Control
1. Fermentation Temperature
Both the non-enzymatic decomposition of α-acetolactate and the enzymatic reduction of diacetyl are temperature-dependent. The higher the temperature, the faster the reaction. Therefore, if the main fermentation temperature is increased or the fermentation temperature is maintained at a higher temperature before the end of the main fermentation, the diacetyl is reduced quickly, and the post-fermentation time of the beer is greatly shortened.
2. Addition of High Sparkling Wine
When the diacetyl content of the fermented beer cannot be reduced normally, try adding 20-30% high-bubble wine and use the yeast from the high-bubble wine to reduce the diacetyl.
3. CO2 Washing
Scrubbing with high-purity CO2 gas produced by fermentation removes volatile diacetyl. Although CO2 washing can reduce the diacetyl content, it resuspends gradually deposited yeast, condensate, etc., which may affect the beer filtration process.
4. Beer Packaging
On one hand, it is necessary to reduce the oxygen content, and on the other hand, it is necessary to control the temperature and time of pasteurization because with an increase in pasteurization temperature, it is easier for acetolactate to decompose into diacetyl under aerobic and higher temperature conditions. Practice has proved that instantaneous sterilization produces less diacetyl than long-term low-temperature sterilization.
5. Beer Storage and Filtration
Inhalation of oxygen during beer storage and filtration accelerates the decomposition of α-acetolactate into diacetyl. Therefore, efforts are made to reduce the inhalation of oxygen during beer filtration, and the content of diacetyl can be controlled under certain conditions. The general process is as follows:
4.1 Convert diacetyl to hydroxybutanone and butanediol.
4.2 Diacetyl reacts with sulfite to form a non-volatile complex to remove the odor caused by diacetyl.
4.3 Reduce diacetyl content by preventing the conversion of acetolactate to diacetyl.
6. Prevention of Bacterial Contamination
If the wort or added yeast is infected with lactic acid bacteria or tetrad, large amounts of diacetyl and acetolactate are produced. Wort or yeast can also be contaminated by other miscellaneous bacteria. Although these bacteria do not produce diacetyl themselves, they can seriously affect the activity, condition, and other metabolic processes of yeast, and may increase the diacetyl content. Therefore, it is necessary to control the hygiene of the brewing process and maintain environmental sanitation to avoid contamination during wort or yeast addition.