Fermentation is the process in which yeast converts the glucose in the wort into ethanol and carbon dioxide gas (CO2), giving beer its alcohol content and carbonation. Once the cooled wort is transferred to the fermentation vessel and yeast is added, the fermentation process begins.
How long does beer fermentation take?
Many new brewers want to know the ideal timeframe for fermenting beer. The truth is, we have no control over the fermentation time. Once we introduce the yeast, they take charge of the entire process!
However, we can adjust certain conditions to shorten or prolong the fermentation period, such as controlling the temperature. This depends on the yeast strain used and the desired characteristics of the beer.
Controlling fermentation temperature
Temperature control is crucial during fermentation and can significantly impact the final product’s quality and fermentation time.
Each yeast strain has its preferred temperature range. Different temperatures within this range will affect the fermentation performance of different yeasts. As a general rule, lower temperatures slow down yeast activity, while higher temperatures speed up fermentation.
The key is to avoid extremes—fermenting at excessively high temperatures, especially beyond the yeast’s recommended range, may result in off-flavors and undesired characteristics. Conversely, fermenting at excessively low temperatures, again outside the yeast’s recommended range, can lead to sluggish fermentation, prolonged process, or failure to reach the desired fermentation levels.
The basic rule of thumb for fermentation temperature
Aim for the lower to medium end of the yeast’s recommended fermentation range. For instance, if the range is 18-22°C, it is advisable to target 19-20°C.
Keep in mind that certain beer styles, like wheat beer, may necessitate more complex fermentation procedures.
10BBL copper beer brewing equipment
How do I know when my beer has finished fermenting?
A common mistake made by novice brewers is relying on the airlock on the fermentation vessel to gauge progress. The airlock serves to ensure that nothing enters the fermenting beer while allowing carbon dioxide (CO2) to escape.
While the bubbling sound from the airlock can be captivating, it simply indicates the release of CO2 from the fermentation vessel. If there are any leaks in the vessel, the CO2 may escape, causing the airlock to stop bubbling.
To determine whether your beer has completed fermentation, there is only one reliable way—using a hydrometer or a refractometer. These devices measure the sugar content of the wort/beer.
The general recommendation for determining when beer has finished fermenting and is ready for packaging is achieving a stable specific gravity (SG) reading over 2-3 consecutive days. This ensures that fermentation has indeed concluded.
What should I do once my beer has finished fermenting?
It is advisable to allow the beer to rest for several days after fermentation. This allows the beer to settle and clarify, with the yeast flocculating at the bottom of the fermenter. If possible, slightly lowering the temperature can aid in clearing the beer.
After fermentation is complete, you can opt to package the beer immediately, prolong the aging process, or make additions such as fruit, oak, or other ingredients depending on the beer style.
For a long time, it was common practice to transfer beer from the primary fermentation vessel to a secondary vessel to separate it from the yeast cake, improving the conditions for packaging. Today, the risks of potential oxidation and contamination rarely outweigh the benefits of secondary fermentation. Secondary fermentation is typically recommended only if bottle or barrel carbonation is desired.
Copper fermentation tank
What should my beer look like when it finishes fermenting?
It’s a bit like Schrodinger’s cat… You could open the top and observe what’s happening inside the fermenter, but doing so might alter the outcome and, in many cases, have adverse effects. If you wish to monitor fermentation progress without exposing the beer to air by opening the fermenter, a transparent fermentation vessel is perfect.
The appearance of beer during fermentation depends on our tiny friends—the yeast. Here’s a summary of what they do after the wort is added:
Lag phase (0-15 hours) | Who’s there?
At this stage, yeast cells awaken and try to comprehend their surroundings.
As they rouse from slumber and begin their day, they seek morning stimulants like oxygen, minerals, and amino acids. Once they’ve found these, they start to realize the abundance of food around them, almost wondering, “How am I going to devour all of this?”
During this phase, there is no airlock activity, and due to residual temperature variations, only a small amount of wort convects naturally in the fermenter.
Growth phase (4 hours – 4 days) | Making friends and feasting
“Well, I need some pals to join me in this feast!” The yeast begins to reproduce and consume the sugars in the wort.
Foamy yeast proteins and sugars start to form and grow. A significant amount of CO2 is generated, causing the airlock to go haywire. Also, as yeast produces alcohol and generates heat, thermal convection within the wort intensifies, gently agitating it in the fermenter.
Most of the alcohol, flavors, and aroma compounds are produced during this phase.
Resting phase (3-10 days) | Let’s tidy up this mess
Once all the easily accessible sugars are consumed, yeast undergoes changes, transitioning from milky white to yellow (from precipitated malt and hop components) and brown (from oxidized hop resin).
Yeast starts absorbing compounds, often considered off-flavors, such as higher alcohols, diacetyl, sulfur compounds, and esters, converting them into more alcohol and other desirable esters.
At this stage, the fermented wort is referred to as “green” beer and hasn’t achieved proper flavor balance. As yeast settles into a dormant state, airlock activity and convection slow down, with any remaining trace amounts of food disappearing from the solution.
Dormant stage (several weeks) | My work here is done
Airlock activity may cease entirely (or sporadic bubbles may appear), and convection comes to a halt. Most yeast cells become dormant, adhering to the bottom of the fermentation vessel. The beer begins to clarify, and flavors mature.
Stainless steel fermentation tank
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