Most stuck fermentations restart with a single intervention. The yeast is alive in there — it just needs the right conditions to wake back up. The fixes below are in escalating order; start with the cheapest, easiest one and only move to the next if it doesn't work.
A stuck fermentation is when the yeast stops working before all the sugars have been consumed. Your hydrometer reads well above the expected final gravity, the airlock has gone quiet, and you're starting to worry. The good news: stuck fermentations are usually recoverable. The bad news: only if you intervene within a reasonable window — after about 10-14 days of sitting stuck, the yeast often can't be revived and you may need to pitch a different strain.
This article walks through how to know if your fermentation is genuinely stuck (as opposed to just slow), what most commonly causes it, and the four interventions in escalating order. If you're not sure your fermentation is stuck at all, start with our why is my homebrew not bubbling guide — many "stuck" ferments are actually fine fermentations with leaky airlocks.
Is it actually stuck?
Most reports of "stuck fermentation" turn out to be something else. The only reliable way to know if you have a real stuck ferment is the hydrometer test.
- Take a hydrometer reading. Sanitise your hydrometer and test jar, draw a small sample, record the gravity. For a Hazy Pale Ale style starting at 1.045-1.055 OG, expected final gravity is 1.010-1.014.
- Wait 48 hours. Don't touch the fermenter.
- Take a second reading. If the numbers match each other AND they're well above expected FG, you have a stuck ferment. If the numbers differ, fermentation is still active — just slow. Wait another 48 hours and check again.
The specific definition: a stuck fermentation is two matched readings 48 hours apart, both well above expected FG (typically 1.020+ for a beer that should be 1.012). Anything below that threshold is either still fermenting or finished. The airlock being silent is not enough to call something stuck — only the hydrometer is.
Don't intervene if your gravity is just 2-4 points above expected (e.g. 1.014 instead of 1.012). Final gravity varies by yeast strain and wort composition. A reading slightly above the "expected" range isn't a stuck ferment — it's just where this specific batch finished. Bottle it and see how it tastes.
What causes fermentation to stall
Three causes account for the vast majority of real stuck ferments.
What's happening
Yeast becomes inactive below its preferred temperature range. For most ale yeasts, that's below 16°C. The yeast is alive, but its metabolism has slowed dramatically. Common in Australian winter brewing or when the fermenter has been moved somewhere cooler mid-ferment.
How to check
Read your stick-on adhesive thermometer. If it shows below 16°C, you've found the cause. Even a temperature drop late in fermentation, when you stop checking, can stall the final few gravity points.
What's happening
You didn't have enough viable yeast cells to fully ferment the batch. Either the packet was old, the yeast was stored badly, or you used a single packet on a high-gravity beer that needed two. The yeast worked initially but ran out of viable cells before fermentation completed.
How to check
Look at the original gravity. If OG was above 1.060 and you only pitched one 11g dry yeast packet, you almost certainly under-pitched. Check the date on the yeast packet — if it was near expiry or expired, viability was likely low.
What's happening
The yeast flocculated (settled to the bottom) before finishing the job. Some yeast strains are highly flocculent and will drop out of suspension when the temperature swings or when they sense the easier sugars are gone. The yeast cells are still alive but no longer in contact with the wort sugars.
How to check
Look at the clarity of the wort. If it's noticeably clearer than it was at peak fermentation, the yeast has dropped to the bottom. This is the easiest cause to fix (see intervention 2 below).
Less common causes include nutrient deficiency (rare with fresh wort kits, more common with high-gravity homemade extract beers) and bacterial competition. Those are situations where you usually have other symptoms beyond just stuck fermentation.
The four interventions, in order
Try these in sequence. Wait 48 hours between each step to see if the simpler intervention worked before escalating.
Warm the wort to 20°C
If your stick-on thermometer shows below 18°C, this is almost certainly the cause and the only intervention you need. Move the fermenter to a warmer room, wrap it in a blanket, or place a brewing belt or heating mat around it. Aim for 20°C gradually — don't shock the yeast with rapid temperature changes.
Within 12-48 hours of reaching 20°C, you should see activity resume. Take a hydrometer reading at 48 hours. If gravity dropped, you're back in business and the rest of this article is academic.
Gently swirl the fermenter
If temperature is fine and gravity is still stuck, the yeast may have settled out too early. Pick up the fermenter carefully and rock it gently in a circular motion for about 30 seconds — just enough to lift the sediment back into suspension. Don't slosh the wort against the lid or splash, which risks oxygen exposure. A slow, gentle rocking motion is all you need.
Reseat the lid, wait 48 hours, take a reading. If the yeast was flocculated but viable, this often restarts fermentation. About 30% of stuck ferments resolve with this step alone.
Pitch fresh yeast
If steps 1 and 2 didn't work, the most likely cause is that the original yeast is depleted or stressed beyond recovery. Time to add fresh yeast.
Open a fresh packet of dry yeast (11g sachet is fine for a 23-litre batch). Sanitise scissors before opening if you can. Sprinkle the dry yeast directly onto the surface of the wort — no rehydration needed. Reseal the fermenter, swirl gently to disperse, and leave it. Most stuck fermentations restart within 24-48 hours of a fresh yeast pitch.
Use the same yeast strain as your original pitch if you have it. If you don't, use a clean American ale strain (like a US-05 equivalent) — it's the safest substitute for any modern ale style.
Pitch a more attenuative yeast
Rare but possible: your gravity has dropped some but stalled high (e.g. expected 1.012, sitting at 1.020). The original yeast may simply lack the enzymes to ferment all the residual sugars. Pitch a different yeast strain with higher attenuation — a clean American or English strain, or a champagne yeast in extreme cases.
This intervention is mostly relevant to high-gravity beers (over 1.060 OG) or to recipes with unusual sugar profiles. For a standard Pale Ale, you almost never need this step.
Most stuck ferments recover at step 1 or 3. Steps 2 and 4 are exceptions, not the rule.
What if nothing works
If all four interventions have been tried over 10-14 days and the gravity still hasn't moved, the batch is effectively finished as far as you can take it. You have three options.
Bottle it as a higher-gravity beer
The beer will be sweeter than intended and lower in alcohol than the recipe promised, but it's still beer. Calculate the ABV from your actual readings (OG and final FG) so you know what you're drinking. The result is often a sweet, malty version of the intended style — not what you planned, but drinkable.
Use the high-gravity sweetness deliberately
Some homebrewers lean into the stuck ferment and bottle it as an "intentional" sweet beer. A stuck Hazy Pale Ale at 1.020 FG tastes more like a lower-attenuated English Bitter than the Hazy you meant to make — not a bad thing, just different.
Dump and rebrew
The honest option if the beer tastes wrong. Stuck ferments that resist all interventions are rare, but when they happen, the resulting beer often doesn't taste right — it can be cloyingly sweet, have unfermented yeast flavours, or carry off-flavours from yeast stress. If you're not going to enjoy drinking the result, it's better to compost the batch and brew again, applying what you learned.
Preventing stuck ferments next time
Three habits prevent almost all stuck ferments.
Use fresh yeast at the right pitch rate
One 11g dry yeast packet per 23 litres for standard-gravity ales. Two packets (or a yeast starter for liquid yeast) for high-gravity beers (over 1.060 OG). Check the date on the packet; aim to use yeast within a year of its production date.
Control fermentation temperature
Keep the wort at 18-20°C for the whole fermentation, not just the first few days. Stick-on thermometer checked daily for the first week and every 2-3 days thereafter. In winter, watch for temperature drops; in summer, watch for spikes.
Take regular hydrometer readings
Take a reading at day 7, then day 10. If gravity is stuck or barely moving, intervene early while the yeast is still viable. Stuck ferments caught at day 7 are much easier to revive than stuck ferments discovered at day 14.
For broader troubleshooting context, see our 10 common homebrew mistakes guide. For the basics of dry vs liquid yeast (which affects pitch rates and freshness), see dry yeast vs liquid yeast. For confirming whether something is genuinely stuck before intervening, see why is my homebrew not bubbling.