How Do You Fix a Stuck Fermentation? Expert Tips!

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What Is a Stuck Fermentation?

You’ve double-checked your recipe. You’ve gone through your mashing, boiling, cooling, and pitching processes. The beer is finally in its fermentation vessel, and now it’s time to relax (ideally with your favorite beer) while the yeast does its work.

But when you check on your fermentation the next day, hoping to find some bubbling activity and a nice layer of krausen, nothing is happening. Radio silence…

Stuck fermentation is one of the most common setbacks in homebrewing. It’s an inevitability that most novice brewers will come across at some point. This issue occurs when the fermentation stalls as the yeast stops consuming fermentable sugars. This leaves the beer under-attenuated, meaning it’s too sweet and lacks the intended alcohol content.

It’s certainly a bummer and one of the most frustrating roadblocks homebrewers (and even professionals) face. But it might not be the end of the world, and there are fortunately a few options for what to do next…

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Common Stuck Fermentation Symptoms

• No bubbling and airlock activity after an initial start (or none at all when you pitch the yeast).
• Lack of alcohol warmth and a flat or sweet taste. One way to describe it is “underdeveloped,” which is exactly the issue.
• No krausen formation. There can also be an early drop in krausen after some forms at the start.
• Gravity readings are not dropping. Keep a log to see if these readings plateau well above the recipe target.

Pro tip: It’s important to note that one or more of these symptoms don’t always confirm a stuck fermentation. The only way to confirm this is to take multiple gravity readings over 48–72 hours using a (calibrated) hydrometer or refractometer.

What Causes Fermentation to Get Stuck?

Temperature Stress

Insufficient heat will slow or halt yeast activity, and a sharp temperature drop or fluctuation can “shock” the yeast into inactivity. Ale yeast typically ferments at 62–75°F, while lager yeast generally ferments in the range of 46–58°F. Consistent heat is key!

Yeast Health and Pitching Problems

Old or expired yeast will have vitality and viability issues, which can lead to fermentation issues. This is especially common in high-gravity beers. Problems such as poor rehydration of dry yeast products, underpitching, or using an inactive starter often result in underperforming yeast. Always follow the recipe’s pitch rate!

Nutrient Deficiencies in the Wort

Nitrogen, oxygen, or other micronutrient deficiencies will deplete the fermentability of the wort. Lack of free amino nitrogen (FAN), especially in all-sugar or adjunct-heavy worts, can cause problems. This issue is especially prevalent when fermenting high-gravity beers or even adjunct lagers.

High Original Gravity or Alcohol Toxicity

Too much sugar or high alcohol can inhibit yeast as it accumulates, or cause fermentation to stall. Poor attenuation will be a major sign. However, be cautious—an uncalibrated hydrometer or user error can cause an incorrect gravity reading, resulting in a false alarm.

pH and Contamination Issues

Both overly acidic (low pH) and alkaline (high pH) worts can prevent the yeast from working correctly. Incorrect pH at pitching can be caused by contamination from wild yeast or even bacteria. Off flavors can also arise due to contamination.

Poor Oxygenation

During the initial lag phase of fermentation, the yeast needs oxygen to build cell walls and multiply. This impacts both yeast growth and attenuation.

How to Diagnose a Stuck Fermentation

Diagnosing a stuck fermentation is the first step and requires both careful observation and measurement. You don’t want to confuse a fermentation that’s simply slower than expected with one that’s truly stuck.

• Check airlock activity: It’s essential not to rely solely on this indicator, but it’s the first sign of a stuck fermentation. A lack of bubbling can indicate the yeast is either stuck or slow, but this can also be caused by leaks or early drop-off. Take gravity readings 24–48 hours apart to confirm!
• Check ambient and fermenter temperatures: If you can keep a log of the wort temperature, look for any sudden drops or spikes.
• Smell and taste for alcohol and off-flavors: If there’s a sweet or syrupy taste or aroma, this suggests residual sugar from incomplete fermentation. A lack of perceived alcohol warmth is also an indicator, but should be confirmed by gravity readings.
• Sanitize and stir gently to check yeast activity: This is an early test to determine if krausen has formed at the top of the vessel. A thin yeast cake or minimal sediment suggests poor yeast growth from a lack of oxygen.
• Check the gravity over 2–3 days: Use a hydrometer or refractometer to check the final gravity (FG) properly. You also want to know your target final gravity as a reference, so check the recipe or yeast specs. For most ales, FG should be between 1.008 and 1.014.

How to Fix a Stuck Fermentation

Once you’ve confirmed that fermentation has stalled, there are several measures you can take to potentially restart the process and save the batch.

• Warm the fermenter slightly: Gently raise fermentation temperature by 2–5°F (1–2°C) while swirling the fermenter lightly to resuspend yeast. This should be done gradually.
• Gently swirl the fermenter: This action will resuspend dormant yeast and (potentially) kick it out of being “stuck” and into the fermentation process. It’s a little like smacking an old TV.
• Check and adjust gravity and pH: Check your pH level and either add potassium bicarbonate to raise it or use citric acid to lower it. If the gravity is off, add boiled, cooled water to dilute it.
• Add nutrients: If the yeast is stalled, you can add energizing nutrients, such as DAP or Fermaid K. Base your addition on the yeast manufacturer’s specifications.
• Pitch fresh, active yeast: You can add (ideally liquid) yeast to energize the fermentation. Ensure it’s well-aerated and rich in nutrients.
• DO NOT oxygenate: This is more of a caution than an actual fix. But you can oxidize the beer in the fermenter and cause more issues by agitating it after fermentation has started.

Preventing a Stuck Fermentation

You won’t have to fix a stuck fermentation if it never happens in the first place!

• Use fresh yeast: Ensure you use yeast with a proper cell count. Using a yeast starter is also a foolproof measure for ensuring proper fermentation.
• Aerate wort: Before pitching, oxygenate the wort by splashing, using an aquarium pump, or a pure oxygen stone. This shouldn’t take more than 60 seconds.
• Monitor and control temperature: Always keep temperatures within the specified range for the yeast strain as indicated by the manufacturer. Use a temperature controller or fermentation chamber if your budget allows. This can include controlling the ambient temperature in the location where your fermentation vessel is situated.
• Keep your yeast happy! Add yeast nutrients or Fermaid when needed. This is especially useful for brewing high-gravity beers or adjunct-heavy brews.
• Sanitize everything thoroughly: This will save you from a wide variety of headaches, including stuck fermentation.
• Don’t over-boil: Avoid excessive boiling, especially if you’re using extract. Overboiling will cause excessive caramelization, which makes sugars less fermentable.

Frequently Asked Questions About Stuck Fermentation

How long should fermentation take?

Ales should take 1–2 weeks for primary fermentation, followed by 1–2 weeks for secondary fermentation (bottling/kegging). Lagers will take 2–3 weeks for primary fermentation, followed by several weeks for conditioning and lagering.

Is my fermentation stuck if it stops bubbling?

Not necessarily! An airlock stopping bubbling doesn’t always mean fermentation is stuck; it could also mean the seal on your fermenter is loose or the yeast has finished its job and is dormant. A loose seal on your fermenter could prevent CO₂ from bubbling through the airlock, even if fermentation is active. Also, the yeast may slow down its activity as fermentation progresses. This leads to less CO₂ production and fewer bubbles.

Can I still save my beer?

Thankfully, yes! You can often save a stuck beer fermentation by gently rousing the yeast, adjusting temperature, adding yeast nutrients, or repitching with a fresh yeast starter.

Should I dump a stuck fermentation?

If the beer has developed off-flavors due to infection or other issues, it’s unfortunately best to dump the batch.

Can adding sugar restart fermentation?

Adding sugar can potentially restart a stuck beer fermentation, but it’s really not a guaranteed fix and is definitely not the first step to try. You need to truly understand the cause before resorting to this, as other factors like yeast health, temperature, and nutrient levels also play a crucial role. It’s certainly not helpful if the yeast is already stressed.

Final Thoughts: Fixing and Avoiding Stuck Fermentation

Setbacks, such as a stuck fermentation, can be annoying or even demoralizing, but this learning curve can be valuable for beginners and experts alike. Being able to troubleshoot is massively important in brewing beer, and dealing with a stuck fermentation is great for improving processes and learning patience!

If you catch it early, a stuck fermentation can be fixed. It’s all about recognizing the symptoms and taking action.

Have any stuck fermentation horror stories? Let’s hear them in the comments. And if you want to set yourself up for success, join our newsletter below for more homebrewing tips, troubleshooting guides, and recipes!

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Patrick Daul Expert Writer

Patrick, based in Chicago, is our expert writer at Craft Beer Me. Cicerone-certified since 2017, he brings a wealth of technical knowledge and refined tasting expertise to every article. With a background in travel, Patrick is passionate about experiencing the best craft beers around the world—sharing his experiences and knowledge through engaging and insightful writing.

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