Stage changes in the beer fermentation process

Beer fermentation is a central part of the beer brewing process. The fermentation process usually manifests itself in four stages: lagging stage, active stage, resting stage and conditioning stage. As a professional brewer, he should effectively control all aspects of fermentation, so that beer can be produced according to plan. Our professional brewers will introduce the changes in the beer fermentation process during the brewing process, and provide reasonable suggestions for you to brew delicious beer.

1. Lag stage of beer fermentation 

When we put yeast in the wort, it goes into what we call the lag phase. Although there are no obvious signs of fermentation at this stage, something is still going on. Yeast absorbs oxygen from the wort and produces sterols, which are essential for yeast reproduction and healthy growth.

2. Active stage of beer fermentation 

Depending on beer style, noticeable fermentation (a layer of foam) can be seen between 24-48 hours after serving. At this point, the yeast is entering the anaerobic phase from the lag phase. During the active stage, the number of yeast cells will increase rapidly and start to consume the sugar in the wort. As the number of yeast cells increases, ethanol and flavor compounds are produced. Once the fermentation has dropped a few points (2 Plato or 0.07 SG), you can start brewing most styles of beer. If the beer is not being spun (for example, you plan to dry hops) then you will see a lot of gas build up and escape from the fermentation vessel (FV). This is carbon dioxide formed by yeast cells breaking down sugar. In addition, a thick layer of foam called Claussen forms on top of the wort. The active phase of fermentation typically lasts 4 to 8 days, depending on: beer style, yeast used, pitch rate and fermentation temperature.

3. Resting stage of beer fermentation 

Yeast growth slows down as beer fermentation enters the stationary phase, however most of the flavor and aroma compounds are also produced during this phase. During this stage, the yeast reabsorbs the diacetyl in the fermentation process, hydrogen sulfide also escapes from the fermenter in the form of gas, Clausen descends, and the yeast begins to precipitate or flocculate. At this stage you will hardly see any change and you have to measure the specific gravity of the wort to detect the degree of decay. You'll know the fermentation is complete once the gravity reading stabilizes at the same level for a few days.

4. Beer fermentation adjustment stage 

During the conditioning phase, the lager can be transferred to bright tanks, paying attention to the ingress of oxygen. When the temperature of beer drops to 0~3℃, the yeast will continue to flocculate and settle. Beers are often slowly "aged" due to the reduction of various undesirable flavor compounds in the beer. In an ale, the desired flavor and aroma may diminish over time. For example, in an IPA where good hop aroma is desired, aging can reduce the hop mouthfeel. Additionally, any oxygen that enters during this stage can damage the overall quality of the beer and shorten its shelf life. This will be seen during the conditioning phase: most of the yeast is shed from the beer (and can be poured), making the beer clearer. The beer becomes "smoother" as the pungent notes are softened or reduced.

The beer fermentation stage is a topic worthy of further discussion. Understanding the process will help us brew better beer. Therefore, we must continue to learn and deepen the technical process.