After a day or so of energetic signs of fermentation, things have gone quiet in the carboy, and it appears fermentation has completely stopped earlier than expected. Homebrewers may be concerned something has gone awry during fermentation.
Fermentation ends only when yeast cells consume all available sugar in a batch. It is normal for the process to slow to the point of assuming it has ended. However, it likely still has more than a week left of fermenting. Consistent gravity readings over the course of a few days will indicate that fermentation is over.
Let’s look at signs of active fermentation and the factors that can determine the length of the process, including temperature, yeast strains, and beer styles. We’ll also cover how you’ll know for certain that fermentation has ended by using a hydrometer.
Did your homebrew beer stop fermenting after 1, 2, or 3 days?
Before diving into how and when homebrew has stopped fermenting, let’s first discuss fermentation and what its different phases look like.
Fermentation happens when yeast cells convert sugar into ethanol and carbon dioxide. It’s as simple as that. In the case of beer, yeast cells consume the sugar in wort (a combination of grain mash and water), and this energy conversion creates alcohol and carbonation.
You should assume total fermentation will take at least two weeks, even if it looks like your beer has stopped fermenting after only 1, 2, or 3 days, as beer goes through three distinct phases of fermentation.
Basically, you can expect three phases of fermentation, from pitching yeast to getting a final gravity reading:
- A lag phase, when yeast is gearing up to get to work in its new environment;
- An active phase, as yeast consumes sugars and a homebrewer can usually see bubbles and other evidence of fermentation; and
- A quiet phase, where yeast hunts down remaining sugars and has stopped expending enough energy to provide clues of fermentation.
When the yeast is first added to the wort, it may seem as though nothing is happening for as little as three hours up to twenty-four hours. This period before observable elements of fermentation is called a lag phase, in which the yeast is acclimating to the wort before it can get to work.
Once the yeast is ready, you will typically see signs of active fermentation, such as:
- Bubble formation: Carbon dioxide is released into the environment because of yeast metabolic activity and bubbles will form on the surface of the liquid. The yeast cells will multiply and soon a krausen, or yeast cake, will float on the surface.
- An active airlock: As more and more carbon dioxide is created, your airlock will be bubbling away at a regular pace.
- Swirling particles in the liquid: Fermentation is a metabolic activity, meaning there will be movement. Particles will move around in the liquid, and either rise to contribute to krausen or fall to create trub, the spent yeast and other particles at the bottom of your vessel.
Active fermentation typically lasts 48-72 hours. This gap can be explained by a few factors, such as temperature, the yeast strain that was used, and the style of beer you’re going for.
For instance, a warmer wort and warmer ambient temperature speeds up the metabolic activity of yeast. The yeast multiplies exponentially and consumes sugar quickly, which creates rapid bubbles before entering a calmer, less active phase of fermentation.
Be careful, though – yeast is a little finicky about temperature and usually prefers a wort environment of about 68-72℉. Consult the package the yeast came in to determine what temperature suits it best.
Some yeast strains begin fermenting faster than others. Belgian-style strains tend to progress quickly, as well as to a Norwegian yeast called kveik. This yeast can tolerate high temperatures and completely ferment in as little as 48 hours from pitching!
The style of beer you’re making plays an enormous part in how long the active phase of fermentation lasts, too. Ales can withstand high temperatures, whereas lagers require a slower, cooler ferment. Ales usually take just a couple of days of active fermentation, while lagers can take a week or so before it appears fermentation has stopped.
The important word here is ‘appears.’ Just because it looks as though fermentation has stopped doesn’t necessarily mean it has — it’s only entered into a quiet phase of final energy conversion. This final period can last another week or more, so have some patience and trust your hydrometer.
If the airlock stopped bubbling, does that mean fermentation stopped?
After yeast has acclimated to its environment, there is a flurry of activity as these organisms race to consume as much sugar as efficiently as possible. Carbon dioxide is produced as a result, and as such, a bubbling, an active airlock is a sure sign of fermentation.
As less and less sugar becomes available, the yeast’s activity slows down, and the airlock may seem sluggish, or bubbling may cease altogether. While it could appear as though fermentation has stopped, it’s possible there are still convertible sugars present, and yeast consuming this remaining sugar may not produce visual cues of energy conversion.
Fermentation is over only once all sugars have been turned into alcohol and carbonation, leaving no sugar behind.
How to know if your beer actually stopped fermenting
A few visual indicators indicate that your beer has completely stopped fermenting, such as a total lack of bubbles or if yeast falls out of suspension. However, the best way to know it’s time to bottle is when gravity readings with a hydrometer are consistent for a few days.
There is no more bubbling or movement after fermentation
As discussed above, as yeast cells consume sugar, carbon dioxide is produced, and homebrewers will notice a lot of bubbles on the surface of their beer. Particles will also swirl around as a result of the yeast’s activity.
Whether within the beer, on the surface, or in the airlock, most movement will stop once fermentation has ended. There may be a stray bubble or two as carbon dioxide escapes the beer, but by and large, your batch will be still.
Yeast falls out when fermentation is complete
When there’s nothing left for the yeast to do, with time it will fall out of suspension. The krausen will begin to dissipate as well, and your beer’s clarity and brightness should improve with these particles out of the way. Krausen can fall when fermentation is just close to ending but has not yet gotten there.
Beer stops fermenting when it reaches final gravity
The only surefire way to know that beer is totally done fermenting is to take gravity readings with a hydrometer for a few days when you think fermentation has ended. Ideally, you would have taken an original gravity reading before pitching your yeast to get a baseline. In conjunction with your final gravity reading, this number is also helpful in determining the ABV of your finished beer.
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Water has a specific gravity of 1.000. Let’s say with the addition of grain mash, your original gravity is 1.050. The reading will go down because alcohol is less dense than water. When you suspect fermentation has ended, take gravity readings for a few days. If fermentation really is over, then these readings will be consistent with one another; for example, you’ll have a reading of 1.014 for three days. Your recipe should include a target final gravity that you’ll aim for.
It’s important to wait for consistent final gravity readings before bottling to avoid the risk of the dreaded bottle bomb. If you bottle before fermentation ends, carbon dioxide will build up in the bottle and possibly cause the whole thing to explode. Investing in a hydrometer and taking the time to take the readings is infinitely better than dealing with broken glass (not to mention wasted beer!).