These are some of the issues that can occur in a batch of beer, along with the potential issues that could be causing the underlining issue.

  • Not enough yeast pitchedWort too hot (yeast stunned/killed)Wort too cold (yeast dormant)Fermentation is fine, but the bucket is not sealed (so you can’t see bubbles in the airlock)Fermentation already complete (look for a ring of “crud” around the inside of the fermenter)

  • Not enough yeast pitchedInadequate aerationWort temperature too lowYeast strain flocculated early (rousing yeast may help)Fermentation is finished, not stuck (take specific gravity to check)

  • The yeast did not absorb diacetylContaminationRacked beer too earlyYeast strain

  • High fermentation temperaturesInadequate pitching rateYeast strain

  • Contamination

  • Contamination. Specifically contamination in conjunction with exposure to oxygen

  • Running off wort too quicklyGrains crushed too finelyA high percentage of wheat or rye

  • Crush too coarseCollecting wort too fastCollecting too little volume of wort per unit of grainPoor lauter tun designWater chemistry was not conducive to good mash (check calcium levels first)The pH outside of the 5.2-5.6 range

  • Maybe the beer was supposed to have a high FGA high percentage of specialty malt in the recipeYeast strainAny of the causes listed under “Stuck fermentation”

  • Use Irish moss (at a rate of 1 tsp. per 5 gallons)Boil too short or not vigorous enough

  • Glassware dirtyWeak fermentationToo little protein in wort (esp. when high amounts of adjunct are used)

  • It may be yeast, not mold (different yeast strains can behave differently)Wort is exposed to oxygen, which encourages surface growth

  • Move bottles to a warmer location for conditioningGive beer more time to conditionBeer and priming sugar not adequately mixed in the bottling bucketYou forgot the priming sugarNot enough yeast left in beer to bottle condition (this rarely happens)

  • ContaminationBeer and priming sugar not adequately mixed in the bottling bucketToo much priming sugar

  • Hops are old and stale

  • Wort cooled too slowly when certain very pale malts usedcontamination

  • Fermentation temperature too highInadequate aerationHigh original gravity

  • Beer exposed to light (especially due to bottling in clear or green bottles)

  • Beer exposed to oxygen during late fermentation or conditioning

  • Beer exposed to oxygen during late fermentation or conditioningLong aging of high-alcohol beers (appropriate in some cases)

  • Some sediment is always presentLet beer fall clear before bottling

  • Be sure all valves are closed before transferring liquid to a vesselCheck to make sure that the rubber grommets are not worn around your valves

  • The fermentation lock was clogged (use a blow-off tube next time)

If you are using a malt extract when brewing, then make sure to check if these are your issues if you are noticing these qualities of your brew.

  • Steeped grains in too much water (over 3 quarts water per pound of grain)Steeping water too hot (over 170 °F)

  • Concentrated wort boilScorching of malt extract (stir in thoroughly)

  • Wort and topping up water not mixed thoroughly

If you are using an all-grain brewing process, then make sure to check if these are your issues if you are noticing these qualities of your brew.

  • Excessive volume of sparge water (collected wort less than SG 1.008 or above a pH of 5.8)Excessively hot sparge water (over 170 °F)

  • Mash sat overnight and the temperature dropped to 120 °F (or below)

  • Overly-long rest at 122-131 °F

  • Poor extract efficiency