6 Ways To Tell if Your Fermentation Is Stuck

When your homebrew stops fermenting, sometimes the fermentation isn’t over yet, and that’s a problem. Stuck fermentation happens when the yeast in your homebrew is no longer enough to continue eating up the sugar in the wort. Your fermentation can be stuck for several reasons, but how can you tell if the fermentation is stuck or complete at a glance? 

You can tell if your fermentation is stuck if you notice no activity in your airlock and no layer of Krausen in the wort. A lack of changes in the hydrometer reading three days after the start of fermentation and a high amount of sugar in the brew is another tell-tale sign.

In this article, you’ll learn more about detecting stuck fermentation and what to do about it. 

What Is Stuck Fermentation?

Before we delve into detecting a stuck fermentation, let me refresh your memory on the concept. Stuck fermentation is when your homebrew starts fermenting but stops halfway or never begins. 

There are many causes of stuck fermentation, but two are more prominent – lack of sufficient yeast and low temperature. When the yeast in the wort is insufficient, there’s only so much sugar it can convert to alcohol before the fermentation stops. 

On the other hand, a cold surrounding won’t energize the yeast in the wort to begin fermentation. Sometimes, the temperature might be sufficient to begin, but the fermentation gets stuck along the line. 

This is often due to changes in the surrounding of the brew (from warmer to cooler temperatures). Below are six ways to tell your fermentation is stuck.

1. No Activity in your Airlock 

The first sign that indicates your fermentation is stuck is the disappearance of bubbles in your airlock after sighting them before. Additionally, the lack of bubbles after 48 hours proves that your fermentation didn’t even start. 

Bubbles around the airlock indicate that fermentation is ongoing. The bubbles form because the action of yeast on the sugar produces carbon dioxide gas. Conversely, when you observe no bubbles up the lock, the fermentation could be complete and not necessarily stuck. However, you can’t be sure unless you take a hydrometer reading. 


Sometimes, the lack of bubbles on the airlock is because it’s not well sealed, and there’s a leakage. In this case, fermentation is ongoing, but there’s no barrier allowing carbon dioxide to express itself in bubbles. Hence, it flows out freely from the fermenter. 

The design of airlocks keeps flies and other insects away from your brew. However, it also allows carbon dioxide gas to release pressure at the top when it tries to escape without letting air in.

So, your fermentation isn’t stuck if you tighten the airlock and notice bubbles after several hours.

The lack of bubbles may also be due to low temperatures. Your brew is too cold for yeast to begin fermentation, and bubbles won’t show as evidence.

Consequently, when you can’t see bubbles on your airlock, tighten it properly and relocate your bucket or vessel to a warmer place.   

2. No Layer of Krausen in the Wort 

One of the signs of active fermentation is a layer of Krause at the top of the wort. Krausen is a combination of nutrients from the wort, yeast cells, and other residues that build up from the mixture in the carboy. 

The Krause begins to form within 24 hours as fermentation becomes more intense with the introduction of yeast. It’s the sign of healthy yeast actively doing its job.

Krausen is a thick foamy layer that emerges from the suspension in the wort and shields the beer from infection. Still, it won’t linger up there forever and will eventually drop with time. 

When the foamy layer crashes, the fermentation is complete. Still, you can take a hydrometer reading to be sure. 

Consequently, when you observe your beer within three days of initiating the fermentation process, and there is no sign of Krausen, it could be stuck. 

It could also be a slow start to fermentation, so give it a little time and check after a week. If no Krausen is in sight and bubbles aren’t forming, it’s the inconvenience of a stuck fermentation you are seeing.   

Why No Krausen

There are many reasons why Krausen is absent in your carboy during fermentation. Some yeast strains produce more Krausen than others. 

Higher temperatures can also reduce the presence of Krausen with some yeast. Generally, this isn’t an issue you should worry about unless bubbles are also absent. 

Most beers would still taste great without the formation of Krausen, and some may form Krausen earlier or later than others. 

3. No Changes in Hydrometer Readings 

The best way to tell if your fermentation is stuck is to measure the specific gravity of your wort using a hydrometer. Take the reading before fermentation starts to know the original gravity of the wort. 

Then check again after three consecutive days. If the values are the same as the original gravity and your brew is still sugary when you taste it, your fermentation is stuck. 

In rare cases, the specific gravity can be higher than the first reading, implying that the brew’s sugar level is rising. That’s not a possibility if you didn’t include more sugar, so allow it to sit for a while and resume your reading after a few days. 

However, if the readings are lower than the first and there are bubbles in the airlock, then fermentation is still on. In this case, you have to wait again for at least a week before rechecking. When the lower readings are stable after a week, fermentation is complete. 

Hence, the hydrometer is a trustworthy instrument that differentiates between a stuck and complete fermentation. 

What is a Hydrometer?

The hydrometer is an instrument for measuring the specific gravity of the wort. It’s a handy tool every homebrewer should have. 

To use the hydrometer, extract a sample of your wort using a siphon or wine thief into another vessel or test tube if you have one. Ensure the wort sample in the vessel is enough for the hydrometer to float inside without hitting the sides or bottom. 

Once the sample is out, lock the fermenting vessel to avoid contaminations or entrance of oxygen. 

Now place the hydrometer inside the wort in the new vessel, spin it a little and observe where the liquid stops in the hydrometer’s scale. For more accurate readings, you might want to invest in a test tube that allows you to determine the values using a meniscus. 

A meniscus is a curve that forms at the top of a liquid inside its container, in this case, a test tube. So, when you observe the meniscus, it’s sometimes lower than where the liquid stopped on the hydrometer scale, which is a more accurate measurement. 

4. Your Homebrew Tastes Too Sugary

If you don’t have any testing equipment (which you should strive to have), you can tell if your fermentation is stuck manually by tasting it. Simply extract a sample of wort from your fermenting vessel into a glass and taste. 

When the sugar content in the wort is high, the fermentation could be stuck or still has a long way to go. This means that the yeast is no longer active or too slow in converting the sugars into alcohol. 

Even when the homebrew is a little sugary, it’s not a good sign. Fermentation is only complete when all the sugars in the wort are gone. 

However, tasting your homebrew isn’t a fail-safe test to know if your fermentation is stuck. It’s an additional way to be sure after sighting no bubbles on the airlock because a sugary brew is also a sign that fermentation is ongoing. 

Generally, tasting is essential in the food industry to confirm if what you’re preparing is ready, develop off flavors, etc. 

5. You Can’t Find Any Sign of Yeast Activity 

You can tell your fermentation is stuck if you no longer notice yeast activity inside the wort. As the fermentation begins with momentum, you’ll notice small lumps of yeasts circulating the wort. They will rise to the top and slump to the bottom. 

That’s a sign of active fermentation, and as time progresses, the yeast will exhaust its energy in consuming the sugar and producing alcohol. 

It then comes out of the suspension and retires to the bottom of the wort. At the bottom, the yeast forms a large residue known as yeast cake alongside other particles in the wort. 

If you can’t spot this initial yeast activity, something is off about your fermentation, and it could be stuck. It, therefore, calls for frequent observation within the first few days of fermenting, or you might think your wort is fermenting while it’s not.


If there’s no visible sign of yeast activity after a few days, the yeast is either insufficient—a case of under-pitching—or the ambient temperature is too low. It could also be that the yeast is dormant and needs to wake up. 

You can try any of these methods below to restart or revive the yeast. 

Revive the Yeast

You can awaken the yeast by using a sanitized spoon to stir it. While at it, do not stir for too long or violently as this can create off flavors by exposing the wort to further oxygen. Reviving sleeping yeast is a delicate process that can compound the issue if you aren’t careful.

Add More Yeast

If you aren’t confident you got the right amount of yeast to pitch your wort, there’s a high chance your fermentation is stuck. You can remedy this by adding more yeast to the fermenting brew. However, adding yeast may not be enough to revive the process unless using a yeast starter.

Adjust the temperature

Temperature can enliven sleeping yeast, but only when you observe that the fermenter is in a cold environment. Under cold conditions, the yeast will be dormant, and you won’t see activity like bubbles or Krausen on the vessel. Changing the temperature can make a difference.

6. Confirm Your Room Temperature 

Temperature is a critical factor that can influence the success of fermentation, whether at home or at the brewery. Your fermentation will be stuck if the surrounding temperature is too low for the yeast to be active. 

There is a specified temperature range for fermentation, which is between 65F (18C) and 75F (24C). Any values below or higher than this range will lead to undesirable results in the final brew or stall fermentation. 

If the temperature is higher than necessary, the beer will ferment too fast, kill yeast cells and lead to off flavors. The yeast will lack sufficient energy to initiate fermentation when the temperature is too low. 

Checking the temperature of your wort regularly is an efficient way to observe how the environment affects its fermenting activity. When you realize the temperature is too low, chances are – your wort is no longer fermenting. 

However, some recipes permit low temperatures to increase unique flavors and produce less of other flavors. Some will also require a bit of a high temperature to produce more of certain flavors.  


When your fermentation is dormant or stuck due to low temperature, you can remedy the situation by adjusting the temperature with the steps below: 

  • Relocate the fermenter to a warm location with little access to air. Eliminate temperature fluctuations in the new environment by keeping doors and windows shut throughout the fermenting period. 
  • To ensure the temperature is high enough to trigger activity in the wort, get a dry cloth and wrap the fermenter or vessel. 
  • When wrapping, I advise you use a comforter, duvet, or any other thick clothing that can generate heat faster. 
  • Additionally, always ensure you haven’t placed the vessel directly on the bare floor, which can be too cold and negatively influence the brew’s fermentation. 
  • Lastly, ensure you monitor the temperature regularly using a thermowell – a simple handheld instrument to measure a wort’s temperature. 

About HomeBrewAdvice

Hello, my name is Simon. Together with a group of writers I write about brewing beer and making wine. We all share a passion for the great things in life, such as making stuff from scratch.

The business of HomeBrewAdvice is to bring you great information, stories and product reviews from brewing at home, and making wine

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