Fermentation appears to have halted before reaching target final gravity

high

Gravity stops dropping above the expected FG. Confirm by reading three days apart; if unchanged for 72 hours, fermentation is genuinely stuck.

Likely causes

CauseProcess articleIngredientNotes
Fermentation temperature dropped, putting yeast into hibernationFermentation control — temperature, schedule, packaging—Raise temperature 2-3 °C and wait 48 hours before any other action.
Underpitched yeast tapped out earlyFermentation basicsFermentis SafAle US-05Repitching a fresh sachet of US-05 will finish almost any stuck ale.
Mash temperature too high produced unfermentable wortMashing — controlling sugar profile and body—A mash at 70 °C+ produces dextrins that no yeast can ferment. Target FG will be higher than expected.
Wort exceeded yeast's alcohol toleranceChoosing a yeast for your beer—Most ale strains tap out at 9-10% ABV. Switch to champagne yeast or a saison strain to finish.

First, confirm

Take a hydrometer reading. Take another 72 hours later. If unchanged, fermentation is stuck. If it moved 2-3 points, you’re not stuck — you’re slow. Slow is fine.

Diagnostic order

In our experience the causes break down roughly:

CauseFrequency
Cold fermentation, yeast dormant~40%
Underpitched at start~30%
Unrealistic FG expectation (high mash temp)~20%
Alcohol tolerance limit~10%

Always rule out cold fermentation first because the fix (raising temperature) is free and risk-free.

Recovery

  1. Raise temperature to mid-range for the strain
  2. Wait 48 hours; confirm with gravity reading
  3. If still stuck: gently rouse the yeast (swirl the fermenter, no splashing/oxygenation)
  4. Wait 48 hours more
  5. If still stuck: pitch a fresh sachet of US-05 directly into the fermenter (no rehydration needed)
  6. If your beer is above 9% ABV and still stuck, pitch champagne yeast — it’ll handle the rest

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