Before You Panic: Confirm It's Actually Stuck

An airlock is entertainment, not instrumentation. Carbon dioxide escapes around a loose lid, a temperature drop pulls liquid back down the trap, and a warm room can push gas out for days after the yeast has finished. Plenty of perfectly healthy brews have been declared dead simply because the bubbling stopped.

What you need is a hydrometer and a little patience. Draw a sample into a trial jar — about 100 ml from the tap, and don't tip it back in — then take a second reading three days later. If the number hasn't moved, you have a genuine stall. A beer that started at 1.048 and is sitting at 1.020 after a week is stuck; one that started at 1.048 and has reached 1.012 is simply done, and no amount of wishful thinking will squeeze more out of it.

A couple of practical notes. Most ales finish their noisy phase in three to five days, so a quiet airlock on day six is normal. And if you're using a refractometer mid-fermentation, remember that alcohol skews the reading — you need a correction calculation, or just use a hydrometer and save yourself the arithmetic.

Temperature Is Almost Always the Culprit

Yeast is a living thing with opinions. Most ale strains are happiest between 18°C and 22°C, cider yeasts around 15°C to 20°C, and wine or champagne strains a touch warmer. Drop below the bottom of that range mid-fermentation and the yeast doesn't die — it goes quiet, settles out, and waits.

A cold snap in an unheated garage or utility room is the classic cause. So measure the liquid, not the room: a stick-on thermometer on the side of the fermenter, or a sanitised probe, tells you far more than the thermostat in the hallway.

• Too cold: wrap the fermenter in a sleeping bag or towel, move it somewhere warmer, or use a heat belt or pad. Bring it up gradually to the top of the yeast's range — around 22°C for most ales.
• Too hot: above roughly 26°C, ale yeast can race, throw harsh solvent flavours and flocculate early, leaving gravity stuck high. Move it somewhere cooler rather than adding more yeast.
• Swings: a brew that drops 5°C overnight can stall even if the average looks fine. Stability matters as much as the number.

Look at Yeast Health and Nutrients

If the temperature is fine, ask how much healthy yeast you actually pitched. An old liquid pack without a starter, dry yeast long past its date, or a single packet into 23 litres of 1.070 wort is a heavy ask. High-gravity beers are hostile places: lots of sugar, plenty of alcohol, and very little oxygen or nutrient to help the yeast finish the job.

Cider makers have it worse. Apple juice is nutrient-poor, and a sluggish ferment is often simply a hungry one. A level teaspoon of yeast nutrient per 23 litres at pitching time, plus a second addition if the gravity crawls, usually sorts it. Also aerate wort or juice thoroughly before you pitch — and never after, when oxygen turns to stale cardboard flavours.

Rouse Gently, Then Re-Pitch

Assuming your gravity is genuinely stuck and the brew is warm enough, try the gentlest fix first. Sanitise a long-handled spoon or paddle and stir the bottom third of the fermenter with two or three slow turns. You're lifting settled yeast back into suspension, not whipping in air, so keep it calm and don't splash. Nudge the temperature up a degree or two, then leave it alone for 48 hours and take another reading.

If nothing has happened, pitch more yeast — but do it properly:

• Make a 1-litre starter with 100 g of dried malt extract, boiled and cooled, aerated well, and pitch it at high krausen — roughly 18 to 24 hours in.
• For dry yeast, rehydrate in 30–35°C water for 15 minutes before pitching. It gives the cells a far better start than sprinkling them onto an alcoholic brew.
• Match the strain where you can. For a stuck cider, a champagne yeast will drag it down to dry without complaint.

What Not To Do

• Don't bottle it at 1.020 hoping for the best. If fermentation restarts in the bottle you get gushers at best and bottle bombs at worst. If you must package, use PET bottles, prime very lightly, and store them somewhere a mess doesn't matter.
• Don't tip it down the drain. A stalled beer at 1.020 is still beer, and it may be perfectly pleasant — just fuller-bodied and sweeter than planned.
• Don't add sugar to restart it. Extra fermentables without nutrients or healthy yeast just raise the gravity and confuse your readings.
• Don't keep lifting the lid. Every peek is oxygen and a chance of contamination.

While You're Waiting: A Note on Coffee

Coffee brewing has no fermentation to get stuck — the fruit is fermented during processing long before it reaches your kitchen, and what you're doing at home is extraction. But the discipline is identical, and it's the same lesson this whole article is built on: measure rather than guess. Weigh your beans, note your grind, aim for water at 92–96°C and a ratio around 60 g per litre, then write it down. A brew log — gravity, temperature, dates, tasting notes — is the single best diagnostic tool a home brewer can keep, whether the fermenter is bubbling or not.