Beer fermentation is a fundamental part of the beer brewing process. The fermentation process typically consists of four phases: lag phase, active phase, resting phase, and conditioning phase. As a professional brewer, it is important to effectively control all aspects of fermentation in order to produce beer as planned.
Lag Phase of Beer Fermentation
When yeast is added to the wort, it enters what is known as the lag phase. Although there are no visible signs of fermentation during this stage, something is still happening. The yeast absorbs oxygen in the wort and produces sterols, which are essential for yeast reproduction and healthy growth.
Active Stage of Beer Fermentation
Depending on the beer style, noticeable fermentation (foam formation) can be observed between 24-48 hours after adding yeast. At this point, the yeast transitions from the lag phase to the anaerobic phase. The yeast cells rapidly multiply during the active phase and begin to consume the sugars present in the wort. As the yeast cell count increases, ethanol and flavor compounds are produced. Once the fermentation has attenuated by a few points (2 Plato or 0.07 SG), most beer styles can be brewed. If the beer is not being clarified (for example, if dry hopping is planned), a significant amount of gas will be produced and escape from the fermentation vessel (FV). This gas is carbon dioxide generated by yeast cells breaking down sugar. Additionally, a thick layer of foam, known as Krausen, forms on the surface of the wort.
The duration of the active phase of fermentation typically ranges from 4 to 8 days, depending on factors such as beer style, yeast strain, pitching rate, and fermentation temperature.
Resting Stage of Beer Fermentation
As beer fermentation enters the resting phase, yeast growth slows down, but most of the flavor and aroma compounds are produced during this stage. At this point, the yeast reabsorbs diacetyl from the fermentation process, while hydrogen sulfide is released as a gas from the fermenter. The Krausen subsides, and the yeast begins to settle or flocculate. There is minimal visible change during this stage, and specific gravity measurements are used to monitor the progress of attenuation. Once the gravity reading remains stable for a few days, it indicates that fermentation is complete.
Conditioning Stage of Beer Fermentation
During the conditioning phase, lager beer can be transferred to a bright tank, taking care to avoid introducing oxygen. As the temperature of the beer drops to 0~3℃, the yeast continues to flocculate and settle. Beer undergoes a slow maturation process, which helps reduce undesirable flavor compounds. In ales, desired flavor and aroma may diminish over time. For instance, in IPAs where hop aroma is desirable, aging can lead to a decrease in hop flavor. It is important to prevent any oxygen exposure during this phase as it can negatively impact the overall quality of the beer and shorten its shelf life. During the conditioning phase, most of the yeast settles and can be removed by pouring, resulting in a clearer beer. The beer becomes smoother as harsh flavors soften or diminish.
The fermentation stage of beer is a topic that warrants further discussion. Understanding the process thoroughly enables us to brew better beer. Therefore, we should continue to learn and deepen our knowledge of the technical processes involved.