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Fermentation that looks stuck usually isn’t, it’s either finished, slower than expected, or fermenting without visible airlock activity. Before doing anything, take a hydrometer reading. If gravity is at or near the expected FG for your yeast strain and original gravity, fermentation is complete and your beer is fine. If gravity is significantly higher than expected and hasn’t changed in 72 hours, you have a genuine stall that needs addressing.
Is it actually stuck? Check these first
- Airlock not bubbling ≠ fermentation stopped. CO₂ can escape through imperfect seals around the stopper or lid without bubbling through the airlock. Gravity is the only reliable indicator of fermentation activity.
- Know your expected FG. Safale US-05 typically attenuates to 1.008–1.012 from a 1.055 wort. Wyeast 1968 (London ESB) stops higher, 1.012–1.016, because of low attenuation. Compare your reading against the yeast manufacturer’s listed attenuation range, not a generic target.
- Give it more time. Most fermentation issues resolve with an extra 3–5 days of patience. Yeast works on its own timeline.
Genuine causes of stuck fermentation
| Cause | Symptoms | Fix |
|---|---|---|
| Temperature too cold | Yeast flocculated early; gravity 5–10 pts above target | Raise to 68–72°F/20–22°C; rouse gently |
| Yeast pitched too warm | Stuck early; possible off-flavors from heat stress | Repitch with fresh yeast at correct temp |
| Under-pitched (too little yeast) | Slow start, stuck mid-fermentation | Add active yeast starter |
| High gravity wort (1.080+) | Stuck at 60–70% attenuation | Pitch a high-alcohol-tolerant strain (EC-1118); add yeast nutrients |
| Nutrient deficiency (mead/wine) | Stuck early, sulfer smell, slow | Add DAP (diammonium phosphate) + Fermaid-K |
| Dead/old yeast | No activity after 72 hours | Repitch with fresh active starter |
Step 1: Warm it up and rouse the yeast
Most stuck fermentations in ale brewing are caused by the yeast flocculating, clumping together and dropping out of suspension, before fermentation is complete. This happens when fermentation temperature drops or when high-flocculating strains (like Wyeast 1968 or White Labs WLP002) finish their most active phase. The simplest fix: raise the temperature to 68–72°F/20–22°C and gently swirl the fermenter to resuspend settled yeast. Check gravity after 24–48 hours. Often this is all it takes.
Step 2: Repitch with active yeast
If warming and rousing don’t restart fermentation within 48 hours, repitch. Make a starter: dissolve 100g of dry malt extract in 1 liter of water, boil 15 minutes, chill to 70°F/21°C, pitch a fresh packet of Safale US-05 or Wyeast 1056, and wait until it’s actively fermenting (12–24 hours). Then pitch the entire starter, active, foamy yeast, directly into your stuck beer. The fresh, actively metabolizing yeast will restart fermentation.
For high-gravity beers (1.080+) or high-ABV wines and meads stuck at 8–10% alcohol, use Lalvin EC-1118 (Champagne yeast). It tolerates up to 18% alcohol and will ferment to dryness in conditions that kill most ale strains. Make a starter with a small amount of the stuck beer to acclimate the yeast to the alcohol environment before pitching the full volume. Lallemand’s EC-1118 data sheet covers alcohol tolerance limits and rehydration protocol.
Stuck mead and wine: nutrient addition
Mead fermentation stalls frequently because honey contains essentially no nutrients, nitrogen, vitamins, and minerals that yeast need beyond sugar. The modern approach (TOSNA protocol) staggers nutrient additions throughout fermentation rather than adding them all at once. For a stuck mead: add DAP (diammonium phosphate) at 0.5 g/L plus Fermaid-K at 0.5 g/L, stir to degas, raise temperature to 70°F/21°C, and repitch with EC-1118. Most stuck meads recover within 48–72 hours with this approach.
Common Questions
My beer has been at 1.020 for 5 days and should be at 1.010. Is it ruined?
Not ruined. It’s stuck, but that’s fixable in most cases. First check: is 1.020 actually within range for your yeast? Check the manufacturer’s listed attenuation, some high-flocculating English strains are done at 1.018–1.020 from a 1.055 original gravity. If it’s genuinely higher than expected, warm the beer to 70°F/21°C, swirl to rouse yeast, and wait 48 hours. If gravity still doesn’t drop, make a starter with fresh US-05 and repitch. Stuck at 1.020 with 5 more points to go is very recoverable.
How long should I wait before calling fermentation stuck?
Take a gravity reading at day 7 and again at day 10. If the readings are identical and both are above your expected FG, it’s been stuck for at least 3 days, act then. Don’t wait more than 2 weeks to investigate, since a genuinely stuck fermentation left too long can develop off-flavors from stressed yeast and bacterial activity. The 3-day confirmation window (same gravity two readings 72 hours apart) is the standard for deciding that fermentation is finished versus stuck.
Can I bottle a beer that’s been stuck and then rescued?
Yes, but only after you’ve confirmed the gravity is stable at its final value for two consecutive readings 48 hours apart. If you bottle before fermentation is truly complete, residual yeast activity creates CO₂ in the sealed bottle, the result is over-carbonated or bottle-bombed beer. Once gravity is confirmed stable at FG, bottle with normal priming sugar (4–5 oz corn sugar for 5 gallons targeting 2.5 volumes CO₂). The repitched yeast will carbonate the beer normally within 2–3 weeks at 70°F/21°C.
