The Stages of Beer Fermentation Process
Beer fermentation is a crucial part of the beer brewing process. The fermentation process can be divided into four phases: lag phase, active phase, resting phase, and conditioning phase. As a professional brewer, it is essential to effectively control all aspects of fermentation to ensure the desired outcome of the beer production. In this article, ACE’s brewer will explain the changes that occur during the fermentation process and provide suggestions for brewing delicious beer.
1. Lag Phase of Beer Fermentation
When yeast is added to the wort, it enters a lag phase. Although there are no visible signs of fermentation at this stage, important processes are occurring. Yeast absorbs oxygen from the wort and produces sterols, which are vital for yeast reproduction and healthy growth.
2. Active Stage of Beer Fermentation
Depending on the beer style, noticeable fermentation (foam formation) can be observed between 24-48 hours after yeast inoculation. During this active stage, the yeast transitions from the lag phase to the anaerobic phase. Yeast cells multiply rapidly and begin consuming the sugars in the wort. As the yeast cell count increases, ethanol and flavor compounds are produced. Most beer styles can be brewed once the fermentation drops a few points (2 Plato or 0.07 SG).
If the beer is not being clarified (such as when using dry hops), a significant amount of carbon dioxide is produced, resulting in gas escaping from the fermentation vessel (FV). Additionally, a thick layer of foam called “Krausen” forms on top of the wort.
The active phase of fermentation typically lasts 4 to 8 days, depending on factors such as beer style, yeast strain, pitching rate, and fermentation temperature.
3. Resting Stage of Beer Fermentation
As beer fermentation enters the resting stage, yeast growth slows down, but most flavor and aroma compounds are still produced. During this phase, the yeast reabsorbs diacetyl, a byproduct of fermentation, and hydrogen sulfide is released as a gas. The Krausen falls, and the yeast begins to settle or flocculate. At this stage, there is minimal visible change, and the specific gravity of the wort needs to be measured to determine the level of attenuation. Once the gravity reading stabilizes for several consecutive days, fermentation is considered complete.
4. Conditioning Stage of Beer Fermentation
In the conditioning phase, lager beers can be transferred to a bright tank while ensuring minimal oxygen ingress. As the beer temperature drops to 0-3℃, yeast continues to flocculate and settle. Beer undergoes a slow maturation process during this stage, which helps reduce undesirable flavor compounds. In ales, desirable flavors and aromas may decrease with aging. For instance, in India Pale Ales (IPAs) where hop aroma is desired, aging can diminish the hop character. It is crucial to prevent oxygen exposure at this stage as it can negatively impact beer quality and shorten its shelf life. During conditioning, most of the yeast settles and can be poured out, resulting in clearer beer. The taste also becomes smoother as any harsh flavors soften or fade.
The fermentation stage of beer is a topic that warrants further discussion. Gaining a deep understanding of the process enables us to brew better beer. Therefore, continuous learning and mastery of the technical process are essential.