If a beer is holding at 1.030 when you expected 1.012, first check whether that expectation fits the recipe and yeast. Then check the measurement and fermentation conditions. Adding yeast or warming the fermenter without a diagnosis can leave the original problem unresolved.
Stable does not always mean finished
Take comparable gravity readings several days apart. A falling reading means fermentation is continuing. Matching readings establish stability during that interval; they do not prove that all fermentable sugar is gone. Cold, stressed, or prematurely settled yeast can stop and later restart, including after the beer has been bottled.
Degas a hydrometer sample, check its temperature, and read the meniscus consistently. If you used a refractometer, correct for alcohol using the original and current Brix readings. An uncorrected reading can make a finished beer look stalled. The hydrometer guide and refractometer correction calculator cover those checks.
Compare the result with previous batches, the recipe, and the strain's typical attenuation range. Those ranges are useful context, not a pass/fail test: wort composition changes the achievable attenuation. There is no universal final gravity or attenuation percentage that proves a beer is ready to bottle.
Check whether the wort can ferment further
A forced fermentation test helps separate limited wort fermentability from a problem in the main batch. A small sample is given plenty of healthy yeast and favorable fermentation conditions, then its terminal gravity is compared with the batch. Follow the procedure in Wyeast's fermentation troubleshooting guidance. Keep the test sample separate and do not return it to the fermenter.
If the sample finishes lower, the main batch has fermentable extract left. If it finishes at the same gravity, that supports limited fermentability, provided the test itself worked. A high mash temperature, some specialty malts, lactose, and yeast strain can all affect the finish. Our mash-temperature guide explains why a higher final gravity does not necessarily indicate a failed fermentation.
What to check in the fermenter
- Beer temperature. Measure the beer or use a probe against the vessel under insulation. Compare it with the manufacturer's range for that strain. If it is too cold, bring it back into range gradually, then give it time and take another reading.
- Yeast condition and amount. Check storage, age, pitching instructions, and the batch's gravity. A pitch-rate estimate helps with planning; it cannot retrospectively measure how many cells survived.
- Early settling. If the strain dropped out unusually early, gentle rocking of a closed fermenter may put yeast back in suspension. Avoid splashing or opening it to stir. Active fermentation does not make oxygen pickup impossible.
- Nutrients and preparation. High-gravity wort and large sugar or fruit additions can change nutrient needs. Review the yeast supplier's nutrient and oxygen instructions. Do not treat oxygen added to nearly finished beer as equivalent to aerating wort before pitching.
- Other stress. High starting sugar, alcohol, low pH, or several stresses together can limit fermentation. A packet's alcohol tolerance is an approximate capability under favorable conditions.
When is alcohol a plausible explanation?
Estimate the alcohol already present from OG and the current corrected gravity. For example, 1.050 to 1.020 is about 3.9% ABV by the standard formula. Alcohol alone would be an unusual explanation for a brewing strain stopping there, but this calculation cannot rule out combined stresses. The table gives context for stronger beers:
| Current gravity | OG for 8% ABV | OG for 10% ABV | OG for 12% ABV |
|---|---|---|---|
| 1.015 | 1.076 | 1.091 | 1.106 |
| 1.020 | 1.081 | 1.096 | 1.111 |
| 1.030 | 1.091 | 1.106 | 1.121 |
OG = current gravity + ABV ÷ 131.25. These are alcohol estimates, not stopping gravities or guarantees about a particular strain.
If a stall is confirmed
Correct an identifiable temperature or settling problem first. If a forced test shows further fermentation is possible but the batch will not move, consult the yeast supplier about a restart culture and acclimation to the beer. A suitable active culture can help, but no fixed starter volume or fresh packet guarantees recovery. Do not repeatedly open, stir, or add ingredients without checking the response.
Do not bottle an unexplained stall
Fermentation that resumes in a sealed bottle generates CO₂ in addition to any priming sugar. Even a modest remaining gravity drop can produce much more gas than intended:
| Bottled at | Additional CO₂ generated | Total CO₂ equivalent |
|---|---|---|
| 1.015 | 5.0 g/L | 3.4 volumes |
| 1.020 | 9.9 g/L | 5.9 volumes |
| 1.030 | 19.9 g/L | 11.0 volumes |
| 1.040 | 29.9 g/L | 16.1 volumes |
Illustration: OG 1.050, fermentation restarting to an assumed 1.010, residual CO₂ estimated at 20 °C, and no priming sugar. The shared fermentation-gas model corrects extract for alcohol. Total gas is expressed per liter of beer; headspace holds some of it, so this is not a dissolved-carbonation or bottle-pressure prediction. Actual bottle ratings depend on the manufacturer and condition of the glass.
Confirm stable readings and an explained, plausible finish before using the priming calculator. It assumes fermentation is complete. If bottles may already be overpressurized, keep people away and avoid unnecessary handling; cooling slows yeast but does not remove existing pressure or establish that the bottles are safe.
Corrected October 10, 2026: stable gravity is no longer presented as proof of completion; alcohol tolerance and the packaging-gas example now state their assumptions.