Common “Off” Flavors – Their Causes and Cures
Before I get into the bad flavors, causes and cures, I want to address the issue of sanitation, the number one cause of bad beer and nasty off flavors in 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!
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.
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:
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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. Sanitation! Sanitation! Sanitation!
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.
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’