Dude! What’s Wrong with My Beer?

Common Off Flavors in Beer – Their Causes and Cures


Before I get into the common off flavors in beer, the bad flavors, the causes and cures, I want to address the issue of sanitation, the number one cause of bad beer and nasty off flavors in beer, home brews and some craft beers. A perfectly crafted and brewed beer can turn into an nasty mess if it is exposed to critters and nasties like wild yeast or bacteria. They can be the cause of almost every off flavor listed below. If your beer develops an unwanted funk and none of the cures take care of the problem, you are probably dealing with an infection. Extreme over-carbonation, gushers, are almost always a sign of bacterial infection, if not just over-priming. Always practice good sanitation with everything that will come in contact with the wort or beer.

Unfortunately, not much can be done to salvage a contaminated batch, other than it being another learning experience. If your beer is victimized by critters or nasties, evaluate your sanitation techniques and Keep on Brewin!

off flavors in beer - not all bad

Good Critters

True, not all bacteria or wild yeast are bad. In fact many styles of beer, particularly Belgian,  utilize the good critters which may be considered off for other styles of beer. Sour beers and Lambic styles require some of the tart or barnyard funk flavors produced by these bacteria.

Brettanomyces – This strain of yeast, commonly known as Brett, and its four known species, claussenii, bruxellensis, lambicus, and bruxellensis trios are present in the ambient air of some regions and are present on the skin of many fruits, and generally live in the pores of wooden casks used to age sour beers and Lambics. Brett slowly takes over after the initial fermentation by Saccharomyces strains has partied out, munching on the complex sugars and other carbohydrates the Sacc. cannot consume. They produce the typical horse blanket and barnyard funk of these very special beers.

Lactobaccillus – This is the bacteria that creates the tang in yogurt and buttermilk. It creates low levels of lactic acid and acetic acid and is typically used after or in conjunction with Brett in sour beers.

Pediococcus – This bacteria produces higher levels of lactic acid and diacetyl, giving a buttery or butterscotch flavor. Along with Brett, it can form a slimy layer on top of the beer called a pellicle that protects it from oxygen and acetobacter. It can also form slimy ropes or strings of carbs and proteins in the beer. These are harmless and will reabsorb into the beer. This is sometimes referred to as the beer being sick. A beer can get sick twice during its aging period.

Off Flavors in Beer - pellicle (2)

Images of pellicle and sick beer.




Acetobacter – Produces high levels of acetic acid, consumes ethanol (alcohol) and turns it into vinegar. Generally not desirable in beer but is present at low levels in some styles. Acetobacter is carried by fruit flies and bees.

All these yeast and bacteria critters are very slow working and can take several months, up to two years to really do their thing. I recommend a full year at least. And, do not forget that sanitation is still important when using these. You don’t want another nasty critter to get into your beer. Also, if you do make a sour or lambic style beer, you still will want to protect your other beers from cross-contamination.

So, now let’s get into the common “off” flavors encountered in beer; what causes them and how to prevent or cure them:

Acetaldehyde –     

Tastes/Smells Like – Green apples, rotten apples

Caused by – It is a naturally occurring chemical produced by yeast which is usually converted into ethanol/alcohol. This process may take longer in high alcohol beers or when not enough active yeast is present.

How to Cure/Prevent – Condition or age the beer for a couple months. This will give time for the acetaldehyde to be converted to ethanol. Always use high quality yeast and be sure to pitch an adequate amount of yeast.

 Alcoholic –

Tastes/Smells Like – Bitter, acetone, paint thinner, spicy, sharp, or hot

Caused by – Fusel alcohols like propanol, butanol, isobutanol, and isoamyl alcohol as well as phenolic alcohols lik tyrosol are usually the source. Limited amounts are OK in high alcohol beers. Caused by fermenting at too high a temperature or leaving the beer on the trub for too long.

How to Cure/Prevent – Avoid fermenting at temperatures exceeding 80°F. If beer is in the fermenter for more than a couple weeks, remove as much trub as possible by racking to a secondary fermenter.

Astringent – 

Tastes/Smells Like – Tart, tannin, drying, puckering sensation, powdery, or metallic, like a grape skin or a tea bag.

Caused by –  Polyphenols or tannins found in the husks of grain or the skin of fruit. Steeping grain for too long or using grain that has been milled or crushed too finely. Mash pH exceeding 5.2-5.6. Tannins can also be extracted from hops, particularly if there is excessive leaf and stem debris in the hops.

How to Cure/Prevent – Avoid over-milling, grains should be cracked open but not crushed or shredded. Pay close attention to sparge temperature. When steeping grains, remove from water before boil. Never add fruit to boiling water or wort. Add fruit in the fermenter or let steep for 15-30 minutes after the end of the boil.

 Chlorophenol –

Tastes/Smells Like –  Plastic, vinyl, iodine

Caused by – Using chlorinated tap water to brew or to rinse equipment. Using cleanser or sanitizer that is chlorine or iodine based.

How to Cure/Prevent – Do not use chlorinated water unless properly filtered or boiled for 15 minutes and cooled to room temperature. Always use cleaners and sanitizers correctly per package instructions. If using chlorine bleach, use 1/2 ounce per gallon of water and rinse with filtered or pre-boiled water

Cidery –

Tastes/Smells Like – Apple cider, wine, acetaldehyde

Caused by – Using too much corn sugar or cane sugar. 1 lb per 5 gallons is generally the upper limit before cidery flavors develop.

How to Cure/Prevent – Cut down on the sugar being used. Use an alternate source of fermentables like malt extract or honey. Lagering may help dissipate cidery flavors over time.

Diacetyl –

Tastes/Smells Like – Butter, Butterscotch, slickness in the mouth and tongue

Caused by – naturally produced by yeast during fermentation and then reabsorbed. Diacetyl not reabsorbed may be due to higher than normal flocculation, weak or mutated yeast, over or under oxygenating, low fermentation temperatures, and weak or short boils.

How to Cure/Prevent – Highly flocculant yeast may fall out of suspension before absorbing diacetyl. Always use high quality yeast and give it sufficient time to fully ferment at appropriate temperatures. Do not aerate or oxygenate after pitching yeast.

Dimethyl Sulfide (DMS) –

Tastes/Smells Like – Cooked vegetables, creamed corn, cabbage, tomato, shellfish, oysters

Caused by – S-methyl methionine (SMM) is created during the malting process and later converted to DMS when heated. Darker grains have less DMS  as kilning converts SMM to DMS and the heat drives it off.

How to Cure/Prevent – DMS evaporates off during the boil. Always maintain a strong rolling boil for at least 60 to 90 minutes. Avoid letting condensation drip back into the wort and never cover the kettle during the boil. Cool wort as quickly as possible. A strong fermentation will help clean up DMS as the CO2 bubbles carry it away.

Estery/Fruity –

Tastes/Smells Like – Fruit, particularly banana or sometimes pear, strawberry, raspberry, grapefruit

Caused by – Naturally occurring by-product of fermentation. Certain ales, primarily Belgians and Hefeweizens, are supposed to have these flavors and certain types of yeast produce more than others. Generally, higher fermentation temperatures will produce more esters. Low oxygen levels can also increase production. Some fruity aromas or flavors can also come from the hops, particularly citrus/grapefruit.

How to Cure/Prevent – Always pitch enough yeast for the gravity of your beer and oxygenate well. Use the correct yeast strain for the style of your beer. Avoid fermenting over 75°F. Fermenting at 60°- 65° will greatly reduce ester production but will make for a slow fermentation.

Grassy –

Tastes/Smells Like – Freshly cut grass, musty

Caused by – Usually the result of grains or extracts which have developed mold or bacteria. Aldehydes can form on old malt giving a grassy flavor. Some varieties of hops have a desirable grassy aroma or flavor. Other hops if not properly processed, excess leaf and stem debris, can develop similar off flavors.

How to Cure/Prevent – Store grains and extracts in a cool, dry, dark place. Check ingredients for discoloration, off smells or tastes. Pre-milled grains should be used within 2 – 4 weeks. Always use high quality, properly processed and stored hops. If ingredients look, smell, and taste good, they should be fine to use.

Husky/Grainy –

Tastes/Smells Like – Raw grain, dry, similar to astringent from tannins or oxidation

Caused by – Over milled grain or highly toasted malts, collecting too much wort from the sparge which can extract tannins from the grain husks

How to Cure/Prevent – Avoid over milled grain that has been shredded or crushed. If toasting your own grains, they should be allowed to age a week or two before use. Do not continue to collect wort from the sparge after the sweet liquor has been rinsed out. You will begin to extract tannins from the grain.

Medicinal –

Tastes/Smells Like – Cough syrup, mouthwash, Band-aid, smoke or clove

Caused by – Phenols brought out during mashing and/or sparging caused by incorrect pH levels, water volumes and temperatures. Improperly using chlorine or iodine based sanitizers. Yeast can also produce phenols and a clove-like flavor is desirable in wheat beers.

How to Cure/Prevent – Follow proper mashing and sparging techniques and specific directions for use of sanitizers . Always use the proper yeast for the style of your beer.

Metallic –

Tastes/Smells Like – Metal, iron, copper, pennies, blood

Caused by – Boiling in unprocessed metal kettles, mainly iron, aluminum, or steel (non-stainless). Can also come from other metallic brewing equipment. Water with high levels of iron. Improperly stored grains.

How to Cure/Prevent – Always use stainless steel kettles and equipment. If using a ceramic coated steel kettle, always check for cracks or scratches. Always use fresh, properly stored grain. Avoid water with iron, such as unfiltered well water.

Moldy –

Tastes/Smells Like – Mold, mildew, musty

Caused by – Almost always the result of storing fermenting beer in a damp, dank area. Using extract,  grain, or hops that have developed mold.

How to Cure/Prevent – Always store fermenter in a dry dark place. Check ingredients for discoloration, off smells or flavors before use. Discard any moldy grain, extract, or hops. If mold in the fermenter is caught early enough it can be removed before it infects the entire batch but, once it is seen, it is usually too late.

Oxidation – 

Tastes/Smells Like – stale or old, wet cardboard, papery, pineapple or sherry

Caused by – Oxygen reacting with the molecules of wort or finished beer. Excess oxygen introduced to the beer while the wort is still warm or after fermentation is complete. Splashing or agitation of finished beer. Too much headspace in bottles.

How to Cure/Prevent – Avoid unnecessary splashing of un-cooled wort or finished beer. When transferring or racking beer from one vessel to another, do so by means of siphon tubing rather than pouring straight in. Keep the end of the transfer tubing below the level of the liquid and avoid air pockets in the tubing. Cool wort as quickly as possible and do not aerate until it is below 80°F. When bottling, avoid splashing and leave no more than 1/2″ headspace. Oxygen absorbing bottle caps are available to reduce oxidation. When kegging, purge kegs with CO2 to flush out air/oxygen.

 Salty –

Tastes/Smells Like – Salt

Caused by – Too much gypsum or other water salts

How to Cure/Prevent – Never add brewing salts unless you know the original salt content of your water and how the salts will effect the water. Certain beers have a slightly salty nature due to the mineral content of the local water such as beers from Burton-on-Trent. There is a German style of beer, called Gose, which actually has sea salt added.

Skunky/Light Struck –

Tastes/Smells Like – Aroma of skunk, musty, burned rubber, cat musk

Caused by – When hops are exposed to UV light from sunlight or florescent light, the alpha acids break down and react with hydrogen sulfide produced by yeast. This creates mercaptan, the same chemical skunks secrete when they spray.

How to Cure/Prevent – When fermenting in a clear container or carboy, keep it covered and out of direct sunlight or florescent light. I cover my carboys with a black T-shirt. All clear containers will let UV light in. Use brown bottles as these filter out nearly all UV light. Never use green or clear bottles. Using isomerized hop extracts can help prevent skunking.

Soapy –

Tastes/Smells Like – Soap, detergent, oily, fatty

Caused by – Keeping beer in the primary fermenter too long after fermentation is complete. The fatty acids in the trub begin to break down and soap is created.

How to Cure/Prevent – Rack beer to a secondary fermenter after fermentation is complete. Do not try to age or lager in the primary fermenter.  Light beers and lagers are more susceptible to soapiness.

Solvent-Like –

Tastes/Smells Like – Paint thinner, nail polish remover, harsh, sharp, burning sensation

Caused by – Combination of very high fermentation temperature and oxidation. Also from use of non-food grade plastics.

How to Cure/Prevent – Do not ferment at temperatures higher than the suggested range for the yeast being used. Never use plastic or vinyl equipment that is not marked as food grade and even then do use with high temperatures.

Sulfur/Hydrogen Sulfide –

Tastes/Smells Like – Sulfur, burning match, rotten egg, raw sewage

Caused by – Hydrogen Sulfide is naturally produced by all yeast during fermentation. Lager yeasts can produce overwhelming sulfur aromas. Ale yeasts produce such small amounts as to usually be unnoticeable. Autolysis, the active yeast begins to consume the dead yeast.

How to Cure/Prevent – During fermentation, CO2 should carry most of the hydrogen sulfide away. Conditioning or lagering after fermentation is complete should make any remaining sulfur smell fade over time. Rack the fermented beer off of the trub which contains spent or dead yeast.

Sour/Acidic –

Tastes/Smells Like – Vinegar, acrid

Caused by – Almost always the result of bacterial or wild yeast infection. Check back to the beginning of this posting.

How to Cure/Prevent – Bacteria and wild yeast are all around us all the time. They are in the air but cannot fly, they can only fall downward. They cannot crawl up and in. Dirt cannot be sanitized; make sure things are clean before sanitizing. Cleaners do not sanitize and sanitizers do not clean. Wort under 180°F is prime breeding ground for bacteria. Cool the wort quickly and immediately pitch a high quality yeast. The faster the yeast starts to ferment the sooner it will over-power and eliminate the nasty critters. But most importantly, Sanitation! Sanitation! Sanitation!

Sweet – 

Tastes/Smells Like – Overly sweet or sugary, cloying, unfermented wort

Caused by – Stuck fermentation, yeast that has quit fermenting prematurely. A sudden drop in temperature can make the yeast go dormant. Using yeast that does not have high enough alcohol tolerance for a high gravity beer can leave too much residual sweetness. Not enough hop bitterness to balance the malt sweetness. Using too much fruit flavoring or other adjuncts.

How to Cure/Prevent – Always use high quality yeast and the proper strain for the beer being brewed. When making a high gravity, high alcohol beer, use yeast nutrients. Avoid fermenting at temperatures below the range recommended for the yeast. Dormant yeast can sometimes be revived by gently swirling the fermenter to suspend more yeast and slowly raising the temperature. If alcohol content has killed the yeast you can re-pitch with a more highly attenuative or tolerant yeast strain.

Yeasty –

Tastes/Smells Like – Yeast, bread, can be harsh or slightly sulfuric

Caused by – Unhealthy or mutated yeast. If beer is left sitting on dead yeast for too long, the yeast begins to eat itself, autolysis, and harsh sulfuric flavors are produced. Young beer in which the yeast has not yet flocculated completely. Disturbing the yeast sediment when pouring from a bottle.

How to Cure/Prevent – Always rack beer from primary fermenter to secondary and leave behind has much trub as possible. Some yeast sediment is unavoidable when bottle conditionong. Take care not to disturb this yeast when pouring unless it is a hefeweizen, in which case you want to re-suspend settled yeast.

I hope that all helps with understanding the off flavors you may encounter. Do not be discouraged, figure out what may have gone wrong and…

Keep on Brewin’

10 thoughts on “Dude! What’s Wrong with My Beer?

  1. I do not even know how I ended up here,
    but I thought this post was great. I don’t know who you are but definitely you’re
    going to a famous blogger if you are not already 😉 Cheers!

  2. Thanks for sharing this post. I’ve always wondered how home brewed beer was made. The process you describe is quite straight forward. Even more importantly I was impressed by your pointing out what could be wrong in beer, like taste or smell and showing how to prevent it. This is a skill I’d definitely love to perfect, will surely be sticking around. Thanks for sharing!

  3. I like this site. I found myself reading about beer and it’s fungi problems.. EW,, I don’t even like beer.

    The layout is good, the reading is easy, I like how you included a link to WA under a “build your own website” page. I may steal this idea. The choice of crisp images is fantastic, and very supportive to the immediate topic.
    Thank you for your thoroughness

  4. WOW! That’s a lot of information – but well organized and in “digestible” bites. My nephew has done some home brewing, but I had NO IDEA how complex and scientific it can be. Love your pictures of “critters” and how you laid out the information. How long have you been brewing? I like your ‘tag line’ too – keep on brewin’ – good attitude. Have you had many batches of beer that have been “learning experiences” from going bad? I also love you blog post title. Grabs the attention well.

  5. Ooh germs. I see a lot of bacteria and yeast in the lab everyday Those things are tiny but boy do they wreak havoc. They grow at an alarming rate and thus have power in numbers. They are every where!; I think they will take over the world before machines do.This is a well written post and addresses the issue of hygiene very well. Other than bad flavor caused by contamination, these germs can cause gastrointestinal problems too when comsumed in large quantities.

  6. wow!!! never thought of finding such pages which provides useful tips on brewing your own beer. Loves it which you not only teach on how in prepping it but as well emphasize on the importance of sanitation & hygiene. For me, without proper sanitation & hygiene practice, it is just pure hazard for us to prepare either food or even beverages. Great post, will be keeping on looking in your post. 🙂

  7. Hi , what a nice blog for avid beermakers . i came across your site looking for answers , maybe you can help . I have a still , and my interest is making rum ,gin,fruit brandys , ouzo ,raki ,absinthe . All these I have mastered to a greater of lesser degree, so I thought I would try and make a whiskey , or at least a moonshine . I was gifted some oats, barley and bought some yellow corn , so I thought I would make a C.O.B. Whiskey , corn oats , and barley . Milled everything in thirds , in a blender, not fine fairly coarse .All I had as a yeast was a white wine type , and alpha amylase to convert the starches into sugars.I boiled up the cob mix and added amylase and continued to simmer for 30 mins as directed on the Hamilton bard amylase .Looking at wort info it says chill it asap after boiling.Closed the boiler and chilled it down on the outside with water, down to 21.o celcius , added the wine yeast , and hey presto its bubbling now 3 days , but with a definite farty smell , similar to playing about with Turbo yeast , which I no longer am a fan of , because there is so much sulphur content in the final wash.So where did I go wrong with my no hop beer ? Hoping you can shed some light on my failure , thanks

    1. I really don’t think you have done anything wrong. I have played around a little bit with distilling but never with oats. You did not say whether the grains were malted or not. Was it just rolled oats? Flaked corn, corn meal, or whole kernel? My best guess for the “farty” smell, which is likely hydrogen sulfide, is from the use of white wine yeast. The yeast will produce more sulfur if it is old or was not properly stored. Also if the fermentation temperature was too high. Another possibility is the grain wort is not providing the proper nutrients for this yeast strain. There is always the possibility of some wild yeast or bacteria getting into the fermentation. I have never used a wine yeast with grains. How old was the grain you were gifted? How was it stored? The good news is, it did ferment, and, since you are going to distill this, the hydrogen sulfide should just boil off and not be an issue. Keep on Brewin!

    2. Just had another thought. You say you boiled up the COB mix. Was it actually boiled or did you add the milled grains to water heated to a proper temperature and let it mash for an hour or so? The amylase will help with the starch to sugar conversion but if the temp was too high you may have gotten some unfermentable sugars or killed of the enzymes altogether.

Leave a Reply

Your email address will not be published. Required fields are marked *