Description: Fresh cut green apples, grass, green leaves, latex paint.

Cause: Early removal from yeast, insufficient fermentation.

Prevention: Make sure fermentation is vigorous using healthy yeast. Allow full attenuation. Leave beer on yeast longer. Oxygenate wort fully. Try another yeast strain. Make sure sufficient yeast nutrients are available. Let beer age longer. Check for possible infection.

Description: Spicy, vinous, warming from ethanol and higher alcohols.

Cause: High fermentation temperatures, excessive yeast growth.

Prevention: Reduce fermentation temperature. Use a less attenuative yeast strain. Check yeast health. Use fewer fermentables. Use fewer sugary adjuncts. Pitch sufficient yeast. Oxygenate wort fully. Check for possible infection. Raise mash temperature. Let beer age longer before consuming.

Description: Mouth-puckering, lingering harshness, husk-like graininess.

Cause: Oversparging, overcrushing grain, boiling grain.

Prevention: Don’t oversparge. Don’t overcrush grain. Don’t boil grain. Don’t sparge with water above 170°F and a high pH (over 6). Use water with lower sulfate content. Use less dark grains (especially black malt). Use less whole hops (especially high-alpha hops or simply large quantities of hops). Avoid use of raw spices, fruit pith and fruit skins.

Description: Butter, butterscotch, movie popcorn.

Cause: Yeast by-product, bacterial contamination, or removing beer from yeast too soon.

Prevention: Try another yeast strain. Oxygenate wort before fermentation. Reduce primary fermentation temperature. Use a warmer/longer secondary fermentation. Use healthy yeast in sufficient quantity. Make sure sufficient yeast nutrients are available (including reducing adjunct use). Check for infection. Allow beer to rest on yeast until fully attenuated. Don’t rack, filter or fine too early. Don’t crash-cool yeast. If lager, raise temperature for a diacetyl rest at end of fermentation. Bottle condition beer at cellar temperatures. Avoid adding oxygen during fermentation.

Description: Cooked corn.

Cause: Insufficient wort boiling, slow cooling, bacterial contamination.

Prevention: Use a long, rolling, open boil. Reduce amount of Pilsner-type malt. Cool quickly before pitching yeast. Check for infection. Make sure you use a healthy, vigorous yeast starter.

Description: Fruity (strawberry, pear, banana, apple, grape, citrus).

Cause: High fermentation temperatures, specific yeast strains, oxygenation issues.

Prevention: Lower fermentation temperature. Try a cleaner yeast strain. Oxygenate wort sufficiently. Reduce original gravity. Check hop variety for fruity characteristics. Avoid carrying over excessive break into fermenter. Pitch a sufficient quantity of yeast (avoid yeast stress). Bottle condition and age beer longer at cellar temperatures to reduce esters.

Description: Fresh-cut grass, green leaves.

Cause: Oxidation of alcohols, use of old or improperly stored hops.

Prevention: Reduce dry-hopping or quantity of whole hops. Avoid oxygen pickup. Check hops and malt for freshness.

Description: Skunky, catty.

Cause: Exposure to sunlight after hops have been added.

Prevention: Don’t expose wort/beer to sunlight after hops have been added. Don’t use clear or green glass bottles. Avoid use of Cluster hops in late hop additions.

Description: Chloroseptic, medicine cabinet.

Cause: Chlorinated water, bleach sanitizers, specific infections.

Prevention: Avoid water with chlorine or chloramines (use RO water if necessary). Avoid bleach sanitizers. Reduce astringency/grain husk sources. Avoid excessive whole hop use. Check for infection.

Description: Iron, copper, coins, blood.

Cause: Metallic contamination from water or equipment.

Prevention: Check water for metallic ions. Reduce water salts. Check equipment condition for rust. Make sure stainless steel equipment is properly passivated. Fully rinse sanitizer. Try using RO water and add salts as needed.

Description: Stale, moldy, cellar-like.

Cause: Oxidation, poor sanitation, old ingredients.

Prevention: Avoid oxidation. Check sanitation. Avoid peat-smoked malt. Check water for freshness and taste. Use fresh ingredients (especially malt and hops).

Description: Stale, papery, cardboard.

Cause: Exposure to oxygen during brewing or packaging.

Prevention: Check for oxygen being introduced into beer post-fermentation. Don’t splash when racking/bottling. Check caps and/or keg seals for good fit. Purge bottles/kegs with CO2 prior to filling. Store beer cool. Drink beer when fresh.

Description: Band-aid, electrical tape, styrene.

Cause: Specific infections, high fermentation temperatures.

Prevention: Check for infection. Check yeast strain and health. Lower fermentation temperature.

Description: Smoke-like, charcoal, burnt.

Cause: Scorched mash or boil, excessive use of dark malts, infections.

Prevention: Check for scorched mash or boil. Check excessive use of dark malts. Check for infection.

Description: Hot burning on palate.

Cause: High fermentation temperatures, excessive yeast growth, infections.

Prevention: Lower fermentation temperature. Pitch a sufficient quantity of healthy, active yeast. Check for infection. Try a different yeast strain.

Description: Lactic acid, citric acid, sharp, clean sourness.

Cause: Infections, specific yeast strains.

Prevention: Check for infection. Check yeast strain. Don’t mash for long periods of time at low temperatures.

Description: Clove, pepper, vanilla, etc.

Cause: Specific yeast strains, hop varieties, fermentation temperatures.

Prevention: Use a different yeast strain and/or hop variety. Adjust fermentation temperature (sometimes higher, sometimes lower, depending on yeast strain and beer style).

Description: Rotten eggs, burning matches.

Cause: Infections, high sulfate water, yeast autolysis.

Prevention: Check for infection. Check water for excessive sulfates. Check yeast health. Check for yeast autolysis (beer left on yeast too long at warm temperatures). Try another yeast strain.

Description: Cooked, canned or rotten vegetables (cabbage, celery, onion, asparagus, parsnip).

Cause: Bacterial contamination, aged ingredients, oversparging.

Prevention: Encourage a fast, vigorous fermentation (use a healthy, active starter to reduce lag time; this is often due to bacterial contamination of wort before yeast becomes established). Check sanitation. Check for aged, stale, or old ingredients (especially old liquid malt extract). Avoid oversparging at low temperatures.

Description: Acetic acid, vinegar-like sourness.

Cause: Infections, oxidation.

Prevention: Check for infection. Check yeast strain. Check for oxidation sources (acetobacter is aerobic).

Description: Bready, sulfury, yeast-like.

Cause: Excessive yeast, insufficient flocculation.

Prevention: Use a more flocculent yeast strain. Allow yeast sufficient time to flocculate. Filter beer or use clarifying agents. Avoid carrying over as much yeast. Age the beer longer. Try another yeast strain.

Aerobic: Required

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Acetic acid, acetaldehyde, white pellicle

Aerobic: No

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Acetic acid, ropey film

Aerobic: Yes

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Acetic acid, caproic, horsey, sweaty, papery white flecks or pellicle, thin body

Aerobic: Yes

Grows in: Wort

Spoilage Traits: Butyric acid, caproic, DMS (at high levels), hydrogen sulfide, indole, isovaleric, mercaptans, phenolic, sulfur dioxide

Aerobic: Yes

Grows in: Wort, Packaging & Storage

Spoilage Traits: Butyric acid

Aerobic: Yes

Grows in: Wort

Spoilage Traits: Indole

Aerobic: Yes

Grows in: Wort

Spoilage Traits: Parsnip or fruity odor, acetic acid, diacetyl, dimethyl disulfide, DMS, fusel alcohols, phenols

Aerobic: Yes

Grows in: Wort, Fermentation

Spoilage Traits: Diacetyl

Aerobic: No

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Acetic acid, caproic, esters (citrus, floral, fruity) ethyl acetate

Aerobic: No

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Lactic acid, Sometimes diacetyl & butadiene, thin body, high carbonation, silky texture. Slow, persistent gush when bottle is opened

Aerobic: Required

Grows in: Conditioning, Packaging & Storage

Spoilage Traits: Butyric & caproic acids, hydrogen sulfide, mercaptans

Aerobic: Required

Grows in: Wort, Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Moldy, grayish or bluish flecks on surface, sometimes fuzzy

Aerobic: Required

Grows in: Wort, Conditioning, Packaging & Storage

Spoilage Traits: Acetic & propionic acids, hydrogen sulfide, mercaptans

Aerobic: No

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Lactic acid, diacetyl, butadiene, slimy transparent ropy pellicle

Aerobic: Required

Grows in: Conditioning, Packaging & Storage

Spoilage Traits: Acetic, lactic, & propionic acids

Aerobic: Usually

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Esters (banana, black currant, pineapple, etc.), phenols (esp. clove-like, peaty, plastic & smoky), diacetyl, DMS, fusel alcohols, solventy esters, thin body, high carbonation, dusty or filmy pellicle

Aerobic: Yes

Grows in: Conditioning, Packaging & Storage

Spoilage Traits: Acetaldehyde, hydrogen sulfide, acetic acid, DMS, phenols, sulfur dioxide

Aerobic: Required

Grows in: Fermentation, Conditioning, Packaging & Storage

Spoilage Traits: Acetic & propionic acids