- John Horn
- January 5, 2021
There are a lot of off-flavors that can rear their ugly heads in your precious homebrew. In this article, we’re delving into what off-flavors are, how you can identify them, and how to avoid or fix them.
Being able to identify off flavors is a valuable skill. It will help you better understand brewing processes and science. It will also help you help and others improve their brewing processes and the quality of their beer.
Off-FlavorsThe list below is alphabetical. There are 27 off-flavors listed here.
Acetaldehyde (C2H40)Taste/Smell: Green apple, jolly rancher, and fresh pumpkin.
Causes: Acetaldehyde is a byproduct of fermentation. It is formed as a step in the production of alcohol. Oxidation can also lead to the formation of C2H4O post fermentation.
How to Detect: Look for true green apple flavors. Don’t mistake this for apple-fruity esters. Sometimes tartness or sourness may also be falsely perceived as acetaldehyde.
How to Avoid: A healthy fermentation will allow the yeast to finish the job of converting acetaldehyde into ethanol. Take precautions against oxygen exposure post fermentation.
How to Fix: If you use kegs, try bubbling some Co2 through the beer. A more involved but more effective method would be to krausen the beer. There is an excellent article on krausening from the American Homebrewers Association here.
AlcoholicTaste/Smell: Boozy, warming to hot, and sharp.
Causes: Fusel alcohols are produced by yeast during fermentation. Most yeast create more of this type of alcohol at higher temperatures, usually, 80 F or warmer.
How to Detect: Fusel alcohols are perceived more easily than other alcohol in beer. You’ll notice a warming or biting in the back of your mouth and throat.
How to Avoid: Ferment at temperatures under 70 F. Use a kveik strain for warm fermentations. Fusel alcohols are produced primarily in the first 24 hours of fermentation. Pitching yeast at your target fermentation temp or a couple of degrees below is critically important. If you need to raise the temp, do so a couple days into fermentation.
How to Fix: Aging will help smooth out some of the hotness.
AstringentTaste/Smell: Tannic; like sucking on a tea bag or chewing up grape skins.
Causes: Over sparging and sparging too hot (above 170 F (77C)) are two causes. Mashing with a high pH (above 5.6) and milling grain to finely can contribute to tannin extraction from grain husks. Over hopping a beer can lead to a high polyphenol content and an astringent beer. Polyphenols are tannins.
How to Detect: Astringency can cause a mouth puckering and drying sensation in your mouth. It is very similar to bitterness. Bitterness is sometimes confused for astringency.
How to Avoid: Don’t over sparge, squeeze the BIAB bag, mash above a pH of 5.6, or mill your grain into flour. Don’t use 8 oz of hops as a dry hop addition in a 5 gallon batch. If you’re doing a large dry hop addition, try dry hopping at a cooler temperature and for a shorter duration.
How to Fix: Depending on the amount of astringency, blending the astringent beer with another beer can be a good way of “fixing” the issue.
Butyric (butyric acid)Taste/Smell: Rancid, strong or rancid cheese, bile and vomit.
Causes: Production of butyric acid is from a bacterial infection. It’s produced by anaerobic bacteria as they consume sugar. This means it’s produced without oxygen. Most commonly butyric acid is produced during souring mashing or kettle souring. It can also result from a poor job of cleaning and sanitizing.
How to Detect: You’ll smell it. It will remind you of vomit. Don’t confuse butyric acid for isovaleric acid (foot cheese odor). Butyric acid is easier to detect in beer with a lower pH (e.g. sour beer).
How to Avoid: Practice good sanitation. If kettle souring, lower the pH to 4.5 before pitching lactobacillus.
How to Fix: Butyric acid is converted to ethyl butyrate by brettanomyces, if there are low levels of butyric acid to start with. Ethyl butyrate has pineapple / tropical fruit flavors and aromas. So, if low levels are present, pitch brett and wait for the magic to happen.
Caprylic (octanoic or caprylic acid)Taste/Smell: Goaty (whatever that means), animal fat-like, rancid, and waxy. Anecdotally, I’ve noticed that it smells like the inside of a Tibetan monastery. I attribute this odor to the use of candles made with yak milk. That’s not a smell most people can identify with but if you’ve smelled it…you know what I mean.
Causes: This flavor develops during conditioning and storage or aging.
How to Detect: This is usually only considered an off-flavor at high levels. At low levels it is likely to be perceived as funkyness in a lambic style beer. If it’s truly rancid it won’t be hard to pick up on but on the lower levels “waxy” is a better description.
How to Avoid: Use an appropriate amount of healthy yeast. Don’t age beer in primary. Store your beer at 50 F (10 C) or cooler.
How to Fix: No known fix.
Catty (p-menthane-8-thiol-3-one)Taste/Smell: Cat urine at its worst. Tomato plant and black currant leaves.
Causes: Chiefly caused from the use of certain hop varieties in large amounts, specifically, hops high in p-menthane-8-3one. One such hop notorious for imparting catty flavors when used heavily is Simcoe.
How to Detect: Girls are typically more sensitive to cattiness in beer. What may come across as a pleasant fruitiness to one person will be perceived as cat urine by another. It is wise to defer to the person that is able to more easily pick up on this off-flavor.
How to Avoid: Don’t use really large dry hop additions of Simcoe, and to a lesser degree, Citra and Strisselspalt
How to Fix: Blending is a good option. It will dilute the overall impression of cattiness and may render it to below threshold levels. Prolonged aging may help decrease this but is not a great option because most likely the catty beer is an IPA and should not be aged.
Cheesy / Footy (isovaleric acid)Taste/Smell: Old socks, feet, parmesan cheese, aged hops and generalized rancidity
Causes: Bacterial infection and using old hops are the two biggest causes. Alpha acids react with oxygen to form this off-flavor in beer that is aged.
Brettanomyces can produce isovaleric acid in beer over the course of several months.
I once had a major bacterial infection while kettle souring that resulted in the most offensive parmesan-foot-cheese-rotting-corpse smell I’ve ever encountered! Not fun.
How to Detect: This off-flavor can be misidentified as caprylic. Look for the cheesy flavors coupled with grassy hop notes.
How to Avoid: Practice good cleaning and sanitation. Pre-acidify to a pH of 4.5 or lower if kettle souring.
Unless this flavor is desired, use fresh hops. Store hops in oxygen free, vacuum sealed bags and keep them in the freezer.
How to Fix: Aging beer will help mellow out the cheesy flavor. According to Milk the Funk, “Brettanomyces can break down isovaleric acid into an ester called ethyl isovalerate.” This results in a “fruity, sweet, berry-like with a ripe, pulpy fruit nuance”. Brett to the rescue!
Chlorophenol / MedicinalTaste/Smell: Plastic, band-aid, medicinal, and spicey.
Causes: Chlorophenols are formed via reactions with chlorine or chloramine in water used while brewing.
How to Detect: If present, this off-flavor is easy to pick up on as it is very offensive and perceived at low levels.. Look for the taste/smell descriptions of plastic and band-aid.
How to Avoid: Filter all brewing water with a carbon filter. It’s imperative to use the filter at its specified flow rate or you’ll end up with either chlorine or chloramine in your brewing water. Alternatively, use a campden tablet (potassium metabisulfite) in your brewing water. Campden neutralizes chlorine and chloramine.
Some brewers choose to purchase reverse osmosis water or distilled water in order to avoid brewing with chlorine or chloramine.
How to Fix: There’s no fixing this one. It’s there to stay. The best thing is to dump and rebrew.
CideryTaste/Smell: Apple cider, wine, and acetaldehyde (green apple)
Causes: Typically, this is caused by using too much simple sugar (cane or corn) in a batch of beer. A good rule of thumb is to avoid adding more than 1lb of sugar in a 5 gallon batch. Warm fermentations encourage the production of cidery flavors.
How to Detect: Look for an apple cider twang when tasting. Most likely it won’t taste exactly like apple cider but it will be evident in the overall flavor profile of the beer.
How to Avoid: Use less sugar in your recipe. If the goal of adding sugar is dryness or a higher ABV, try using more base malt and make sure you are mashing low (149 F). Some brewers suggest using honey in place of sugar in order to avoid cidery off-flavors.
How to Fix: Once this flavor is produced it’s there to stay.
DiacetylTaste/Smell: Buttered popcorn from a movie theatre. It can also present as butterscotch.
Causes: Diacetyl is a byproduct of fermentation. Yeast produce it and clean it up. More diacetyl will be produced during slow starting fermentations because yeast make more at the start of fermentation. This means a long start will produce a lot and it can be too much for the yeast to clean up.
Other causes of DMS include mutated yeast and bacteria.
How to Detect: Some people are more sensitive to diacetyl than others. A lot of people notice diacetyl from a slickness on the roof of their mouths. If you feel this, look for buttery popcorn but don’t invent it. Confirmation bias is real!
If diacetyl is a recurring issue for you, try performing a “D” test before packaging your beer.
How to Avoid: Pitch an appropriate amount of healthy yeast. If lagering, perform a diacetyl rest.
How to Fix: Krausen the beer.
Dimethyl Sulfide (DMS)Taste/Smell: Canned and cooked vegetables. The classic description is cooked corn and cabbage.
Causes: DMS is a byproduct of boiling wort. It is formed from it’s precursor S-methyl-methionine (SMM). SMM is produced during the malting process. DMS can form if SMM is present anytime wort in hot. DMS can also result from having bacteria or wild yeast in your brew.
How to Detect: Remember to look for those canned and cooked vegetable flavors.
How to Avoid: The classic advice is to boil for 90 minutes if using pilsner malt. With modern malts and a typical homebrewing setup, a 30 minute boil should be sufficient to effectively boil off all the DMS. Most brewers are going to use a 60 minute boil and that is certainly long enough. The exception to this is if you are using a heritage malt produced with traditional malting methods.
Other tips include keeping the lid off your kettle and ensuring a vigorous boil. Also, chill rapidly if possible.
How to Fix: There’s not a lot you can do to fix this one. Aging may help decrease it a little.
Estery / FruityTaste/Smell: The most common ester is banana. Sometimes apple, pear, raspberry, and strawberry.
Causes: Yeast produce esters as a function of fermentation. Some strains produce more than others. Hefeweizen strains, for example, produce large amounts of banana esters.
In general, high temperatures, less oxygen, high gravities, temperature swings during fermentation, and adding yeast nutrient to a fermentor will all lead to an increase in ester production. For a deep dive into the science behind esters and fusel alcohols take a look here at Scott Janish’s post on the topic.
How to Detect: Look for those signature fruity flavors.
How to Avoid: Ferment at lower temps, adequately oxygenate wort prior to yeast pitch, avoid tremendously overpitching, and ferment underpressure. All those will lead to less ester production
How to Fix: Aging beer will lead to lower ester levels. This would be inappropriate for styles like Hefeweizen which should be consumed fresh because of desirable ester content.
GrassyTaste/Smell: Freshly mown lawn, green leaves, and chlorophyll.
Causes: Improperly stored grain and poor processing of hops can lead to formation of this off flavor. Specifically, aldehydes can form on malt when stored in a damp environment.
More recently, high amounts of dry hopping have led to an increase of grassy and vegital off flavors.
How to Detect: When tasting, look for the characteristic tastes and smells mentioned above. You’ll find with beers that are highly hopped and served really fresh that they will burn or stick in the back of the throat. This is known as hop burn and goes hand in hand with some of these grassy, vegital type off-flavors.
How to Avoid: Store grain in a cool and dry area. Use freshing milled grain. Use high quality hops and store them properly. Decrease dry hop addition amounts, time, and temperature.
How to Fix: If the issue is an overly vegital beer from a lot of hops, giving the beer time for hop particulates and yeast to settle out will usually help take the edge off.
Husky / GrainyTaste/Smell: Raw grain and wet cereal grains or straw
Causes: The most commonly cited cause is overly milled grains. This combined with poor sparging technique can be a cause. The actual culprit is the compound isobutyraldehyde along with other aldehyde compounds. It is found chiefly in fresh malt.
How to Detect: This is a hard one to figure out. It’s so similar to astringency and oxidation. Focus on looking for the signature wet cereal grains or wet straw characteristics when tasting.
If you’ve ever malted barley at home or been around steep and sprouting grain, you’ll recognize the aroma and flavor.
How to Avoid: Stay away from using really fresh malt (probably not a problem for most people). Avoid over crushing grain and sparging too hot (above 170 F) or above a pH of 5.6.
How to Fix: Cold conditioning may help decrease the graininess profile..
Lightstruck / Skunky (3-methyl-2-butene-1-thiol)Taste/Smell: Skunky, cat-musk, and sometimes burnt rubber.
Causes: A result of a reaction between riboflavin and alpha acids caused by sunlight and artificial light (fluorescent). Occurs in beers fermented or packaged in clear and green bottles.
How to Detect: Grab a bottle of TsingTao or Corona and you’ll quickly become acquainted with this flavor. If present in a beer, it isn’t (in my experience) subtle.
How to Avoid: Ferment and store beer away from light sources.
How to Fix: No known fixes. May decrease with aging.
Mercaptan (ethanethiol)Taste/Smell: The same smell as propane. Some describe it as rotting veggies or the smell emitting from a rotten drain.
Causes: Yeast produce mercaptan, however, it would seem that these levels are typically below threshold. Yeast cell death (autolysis) also produces mercaptan. The most likely culprit in beer is production from a bacterial infection.
How to Detect: Look for the butane/propane smells with which you are probably familiar.
How to Avoid: Sanitization is king! Don’t leave a beer in primary for more than a month.
How to Fix: There’s no fixing ethanethiol once it’s in your beer.
Metallic (ferrous sulphate)Taste/Smell: Iron i.e. blood-like, pennies, copper, and rusty.
Causes: Exposure of boiling wort to unprocessed metallic surfaces while brewing (not including stainless steel). Water with a lot of iron and grain that isn’t stored correctly are two more probable causes.
How to Detect: This one will be obvious. Metallic says it all.
How to Avoid: Test your water and avoid using water with high amounts of any metals. Use food grade brewing equipment.
How to Fix: No fixes. Metallic flavors will likely become more prominent with aging.
Moldy / MustyTaste/Smell: Moldy, musty, damp basement, and cellar.
Causes: Exposure of wort or beer to mold or other fungi followed by infection. Most mold doesn’t grow well without oxygen.
How to Detect: The moldy and musty smell says it all. Most likely, you’ll be able to see mold growing in the bottle or fermentor.
How to Avoid: Most mold doesn’t grow well without oxygen. Make sure your fermentor is sealed correctly and your airlocks are topped off, especially, if you are aging beer in a secondary.
How to Fix: Like many off-flavors, there’s no going back…dump it and move on!
Mousy (tetrahydropyridine (THP))Taste/Smell: Mousy, Cheerios® or Cap’n Crunch®, cracker, biscuit.
Causes: THP is a byproduct of brettanomyces, lactobacillus, acetic acid bacteria, and mould.
How to Detect: Many people seem to be blind to THP. A low pH makes it harder to detect. It comes across as “mousy” when higher in content and “breakfast cereal” when lower. Trust the person that picks up on it, even if you can’t.
How to Avoid: If THP is undesirable for the first 2-6 months of your beer’s life, don’t brew with brettanomyces or lactobacillus.
How to Fix: Aging for 2-6 months will take care of THP in most situations. Some brewers have cited examples taking as many as 12 months but this seems more rare.
OxidationTaste/Smell: Wet-cardboard, sherry-like, papery, increased harshness, and staleness.
Causes: Exposure to oxygen post fermentation. Oxidation occurs in every beer made but to many different degrees. Temperature and time are the two biggest factors. Warmer temps and more time will increase oxidation rates.
How to Detect: Arguably, most easily detectable in highly hopped beers that will present as dull and flabby as opposed to bright, bold, and hoppy. Oxidation can change in characteristic as aging occurs. It never does IPAs any favors.
How to Avoid: Purge kegs completely with CO2. Avoid any open air transfers if possible. When bottling, take special care not to splash, slosh, rouse or create foam in any way. Ideally, bottling would be done into a CO2 purged bottle with a beer gun.
Store beer at 50 F of cooler. Age beer only if appropriate for the style.
How to Fix: No fix.
SaltyTaste/Smell: Tastes like salt…must be salt.
Causes: High sodium content on source water. Using too much epsom or gypsum salt or other brewing salts. Adding brewing salts without knowing the base water profile.
How to Detect: Saltiness is most easily perceived on the front side of your tongue.
How to Avoid: Get a water report, respect the upper limit of recommended sodium content. The advised amount is generally 0 – 150 ppm.
Don’t add brewing salts unless you know your base water. Dilute source water as needed to obtain your desired sodium content.
How to Fix: Blend with another beer to dilute high sodium content. I recommend this only after testing the blend at a smaller ratio.
SoapyTaste/Smell: Soap
Causes: Caused by the breakdown of fatty acids found in trub. This can happen if a beer is left in primary fermentation for a long time. The result is literally the formation of soap in the beer.
Other causes could be inadequate rinsing of brewing equipment or glasses after washing.
How to Detect: It will be obvious. We’re all familiar with soap.
How to Avoid: Don’t use soap with any kind of perfume or additives. Use OxiClean or PBW and rinse really well when cleaning equipment. Avoid leaving beer in primary for longer than necessary to achieve complete fermentation i.e. longer than 3 – 4 weeks for most beer.
How to Fix: No fix. Dump it baby.
Solvent-like (Isoamyl Acetate)Taste/Smell: Nail polish remover.
Causes: Produced by brettanomyces is the presence of oxygen. Produced at some level by all yeast during fermentation.
How to Detect: Isoamyl Acetate presents as fruity banana at low levels and isn’t usually considered an off-flavor as such. In higher amounts, it reeks of nail polish remover. Easy to smell.
How to Avoid: When aging beer with brettanomyces, make sure to avoid excessive exposure to oxygen. Take steps to prevent high ester production with ale and lager strains.
How to Fix: Once it’s there at high levels, it’s there to stay.
Sour (Acetic acid)Taste/Smell: Tart, vinegary, apple cider vinegar, and acrid.
Causes: Most likely a result of wild yeast or bacteria. Acetic acid (think vinegar) is produced by both bacteria and brettanomyces.
How to Detect: Look for apple cider vinegar specifically when tasting.
How to Avoid: Practice good sanitation.
How to Fix: No known fix.
Sulfur / Hydrogen Sulfide (H2S)Taste/Smell: Hard boiled eggs, a burning match, and (certain) hot springs.
Causes: Hydrogen sulfide is a normal byproduct of fermentation by yeast. Another cause could be a bacterial infection. Yeast cell death (autolysis) will also lead to some H2S production.
How to Detect: Look for those sulfur-like aromas post fermentation.
How to Avoid: Pitch a healthy and appropriate amount of yeast. Practice great sanitation.
Give time for yeast to clean up. Ales usually don’t have as much H2S post fermentation because they ferment warmer and therefore more vigorously. If you lager, give it time and make sure there isn’t any sulfur aroma before packaging.
How to Fix: If you keg, try bubbling some Co2 through your keg in order to “scrub” out the sulfur.
SweetTaste/Smell: Really sweet and cloying.
Causes: The main causes are poor attenuation by yeast or a stuck fermentation. It is possible that a poorly designed recipe could be the culprit as well.
How to Detect: A lot of beers have an element of sweetness that is appropriate. It is important to be familiar with the style of beer before determining that it is inappropriately sweet. That said, when sweetness is an off flavor it is obvious. We’re all very well acquainted with the flavor so detecting it is easy!
How to Avoid: There are many reasons yeast don’t attenuate as far as they should. To avoid stalled fermentations and poor attenuation, pitch a proper amount of healthy yeast. Take the time to make a starter if necessary.
Make sure your wort is adequately oxygenated when you pitch your yeast. Control your fermentation temp if possible.
How to Fix: If the issue is a stuck fermentation, take steps to help the yeast finish the job.
YeastyTaste/Smell: Yeast and possibly a little bit sulphur-ish.
Causes: Most likely yeast are still in suspension. Could be a poor flocculating yeast strain or a young beer. Poor pouring techniques can lead to excessive yeast in your glass and yeasty flavors in your beer. Poor yeast health and mutated yeast can also lead to yeasty off-flavors.
How to Detect: If you need practice with yeasty off-flavors, swirl up some of the yeast on the bottle of your next homebrew and pour a little in your beer. Once you know what to look for, it’s easy to identify.
How to Avoid: Just like avoiding so many other off-flavors, pitch the correct amount of healthy yeast! Give your yeast enough time to flocculate and cold crash your beer. Take care when pouring bottle conditioned beer.
How to Fix: Fining or other clarification methods will help fix a yeasty beer.
Final ThoughtsThere are a lot of off-flavors! We just went over 27!
It is a good idea to remember flavors are off-flavors when they shouldn’t be found in a specific beer style or maybe when you don’t like them in your beer. Some off-flavors are appropriate in certain beer styles or at certain levels. At which point, they can be considered flavors and not “off-flavors”.
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