The Beer Changes Happened During Secondary Fermentation
During the secondary fermentation process, a number of physical reactions, chemical and biological reactions are still slowly taking place to improve the final flavor of the beer. For example
After primary fermentation, the beer temperature should be 3-5°C to allow further fermentation of the remaining fermentable sugars (e.g. maltose and maltotriose). The carbon dioxide produced will then be dissolved into the beer in a sealed tank to saturate it with carbon dioxide. Moreover, diacetyl can be rapidly reduced as the secondary fermentation temperature increases.
The carbon dioxide formed at the beginning of the secondary fermentation will be blown away. At the same time, odors and volatiles in the beer can be expelled along with the carbon dioxide, thus promoting the maturation of the beer.
After 7-10 days, the beer is gradually cooled to 0-1°C. As the temperature and PH value decrease, yeast, cold residue and hopefully resin begin to settle, making the beer clear and better tasting.
As the temperature decreases, the proteins that tend to cloud the beer also begin to separate and precipitate. They will be removed during the filtration process. This helps to improve the abiotic stability of the beer and thus extend the shelf life of the beer very well.
During the secondary fermentation process, the beer should be protected from air contact. Otherwise, the flavor, foam, color and abiotic stability of the beer will be deeply affected by oxidation and will be easily contaminated.