How Easy for an 85 Beer to Become Infected

How to Identify & Control Off Flavors in Beer

Every beer is made up of a complexity of flavors and everyone perceives this flavor-makeup differently. You may find you really enjoy a certain beer, while your buddy takes one sip and sits back in horror as you happily drink something they find abominable. We each have higher sensitivities to certain flavors creating a unique standard of what we find pleasant or abhorrent. But, in general there is a set of flavors that are considered "off" or faulty when found at a certain level (or any level) in beer.

Some of these flavors are present in almost all beer to some degree and considered an "on" flavor except when its level gets too high for a given style (fruity esters). Other off-flavors are less frequently found, but still are appropriate in small quantities in specific styles (a buttery flavor in some lagers). Then there are those that are never appropriate no matter their level or the beer style (baby vomit… yeah, baby vomit is an off-flavor).

Learning to recognize, then control, or eliminate these off-flavors appropriately takes time and practice.

Cause and Control

Cause and control of flavors go hand in hand. Once you learn what causes a given off flavor in your beer you can better manage your brew day and beer handling to either control or eliminate the cause. The causes of different flavors should be purposely taken into consideration and accounted for by the brewer. Maybe not minutely, but the broad picture at least. Half of brewing is art after all. So, any accidental flavors are "off," at least until you, the brewer, decide they are not.

Some off flavors, especially those resulting from contamination are almost always going to be considered faulty. Though there may be the occasional epiphany of wild yeast contamination making something beautiful. These off flavors are usually caused by poor sanitation and, less often, poor brewing practices.

Any off flavors not arising from contamination are always a result of your brewing practice such as uncontrolled fermentation temperatures, waiting too long to rack to a secondary, weak boils, poor bottling technique, or simply choosing the wrong yeast.

Practice

To practice, you need to taste the "off" flavor in beer. There are different ways to do this. In some cases the flavor makes up the profile of a commercially available beer; where I was aware of such a beer the information has been included. You can also find flavor sensory kits available from places like the Siebel Institute and Flavoractiv which can help you learn different flavors. They aren't cheap, so if you can, go in with a group of fellow brewers who want to better their craft. Third option is the cheap alternative of "homegrown" practices you'll find below. These aren't perfect, but in most cases they will give you a reasonable representation of the off flavor.

These practices should be performed with a light bland lager to eliminate flavor complexity and make it easier to pick out the off flavor. If you've done the practice with a bland lager and want to up the ante by adding it to other beer styles…go for it! This can only make you better, but always start with the basic practice first. I give specific steps for each flavor, but the basic steps, appropriate for all off-flavor practice are the same.

General Off-Flavor Practice Guidelines:

1. Use a bland light lager as your base.
2. Chill the beer to the style's appropriate serving temperature (40-45°F for most lagers).
3. Always have a control—an unflavored beer of the same kind, at the same temperature—for compression.
4. Add small measurable amounts of flavoring until you can perceive the off flavor in both the aroma and taste.
5. Take notes as you progress. What are your measurements? When do you think you begin to perceive the flavor in the aroma? In the taste? When do you know for certain you are smelling and tasting the practiced flavor? What descriptors come to mind at different levels of intensity? Etc.

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1. Diacetyl (2,3-butanedione)

• Perceived As:

  Buttery, buttermilk, milky, oily. Lower levels can appear almost Caramel-like; at higher levels Buttery or butterscotch — think movie popcorn. It can cause a milky or slick sensation on the palate. Easier to detect in light lagers, any added complexity in a beer such as darker more robust flavors will make detection more difficult.

• Approx. Flavor Threshold:

  0.04 mg/l (milligram per liter)

• Importance:

  It is usually considered an off flavor, but is appropriate at low levels in some styles, including English Bitters, Scotch Ales, Dry Stouts, and Czech Pilsner to name a few.

• Effect of Aging:

  Diacetyl can become more pronounced over time in packaged beer that has the precursor of diacetyl, alpha acetolactate. As the alpha acetolactate breaks down it forms diacetyl. Heat accelerates this breakdown.

• Caused By:

  It is produced by all yeast during fermentation, but is usually reabsorbed by the yeast cells. Non-reabsorption or over production is caused by feeble or short boiling, low temperatures during fermentation, mutated yeast, or racking too soon. It can also be formed by bacteria contamination.

How To Avoid/Control:

• Always boil vigorously for the appropriate amount of time.
• Aerate your fermentation well when you cast your yeast. Avoid oxygenating the wort further once fermentation has begun.
• Up your temperature slightly as you near the end of fermentation. This helps the yeast reabsorb diacetyl.
• Don't be too quick to rack your young beer off the yeast. Ensure the little guys are done doing their work before you move your beer off of them.

How To Practice:

To practice detecting diacetyl go to your local grocer and pickup some butter flavoring — preferably in a bottle that has a dropper. Follow the "Basic Practice Guidelines," adding this in small measured doses (one drop at a time). Compare the aroma and taste to the control. Can you detect the diacetyl? You should. But if not add another drop and compare again. Do this until you can smell and taste the butter note when compared to the control.

For further practice you can do the same thing with different commercial beers of varying complexity. This will make it harder to detect the diacetyl.

Commercial Example — Pilsner Urquell is a commercial example that has diacetyl as part of its flavor profile.

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2. Mercaptan (ethanethiol)

• Perceived As:

  Rotten vegetables, drain-like, sulphury, leek-like, or rotting garbage. This is also the compound they put in propane and natural gas to make it odorous, so it may remind you of propane or natural gas.

• Approx. Flavor Threshold:

  1 µg/l (microgram per liter)

• Importance:

  Can make up a component of the sulphury character of some beer styles, but is always considered an off flavor if above the tasting threshold.

• Effect of Aging:

  This sort of contamination will probably not dissipate with aging, and may increase.

• Caused By:

  Mercaptan is most often caused during fermentation by certain yeast strains. It is also caused by yeast autolysis, but a more likely cause of this off-flavor at detectable levels is infection by anaerobic bacteria.

How To Avoid/Control:

• Ensure you always practice good sanitation.
• To avoid possible mercaptan pick up from dead yeast, siphon your beer off the yeast within 4 weeks of fermentation start.

How To Practice:

Ethanthiol is one of the smelliest things you'll probably ever come across in beer — if you're unlucky enough to come across it. You don't need practice. If you think you do take a wiff at your garbage disposal or take the cover off your bathtub drain, pull out some of the gunk in there… yeah, like I said: You don't need to practice.

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3. Lightstruck (3-methyl-2-butene-1-thiol)

• Perceived As:

  Skunky, sunstruck, sulfury. Can be much the same perception as mercaptan but usually does not get to the same offensiveness.

• Approx. Flavor Threshold:

  4ng/l

• Importance:

  This only occurs in finished beer and is always an off flavor. For consumer's it has become part of the flavor profile of several well-known imported beers because of the beers' continued poor handling, shipping, and storage.

• Effect of Aging:

  Generally will increase slowly with aging. It will happen with increased speed if beer is not stored in darkness.

• Caused By:

  Lightstruck is caused by a chemical reaction between daylight or artificial light, riboflavin in the beer, and hop alpha acids. Some commercial breweries use chemically modified hop alpha acids which do not react with riboflavin, allowing them to continue to use their signature green or clear bottles.

How To Avoid/Control:

• Buy commercial beer in cans or brown bottles. If you buy clear or green bottled beer, be very careful about storing them in darkness.
• When drinking a beer keep your bottle or glass out of direct sunlight especially if it's heavy on the hops. It takes a very short time to start the reaction and once started there's no way to stop it.
• Keep homebrew away from light, whether fermenting or packaged.
• Package your homebrew in kegs or brown bottles. These bottles only let in 5-30% of light through, while green glass allows 50-80%, and clear glass allows a whopping 90% through.
• Use fewer hops.

How To Practice:

You can easily practice spotting lightstruck by simply grabbing a couple bottles of the same beer, pour them both into a glass, put one in direct sunlight, and the other keep in relative darkness. After a few minutes see if you can tell the difference. If not let it go a little longer in the sun and try again. You can also do the same thing by placing a bottle of beer in the sun for a day or two.

Commercial Example: Corona and Heineken are two commercial beers that have the lightstruck signature, which many consumers assume is part of their profile.

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• Perceived As:

  Rotten eggs, sulfury, sewer. May remind you of the smell close to hot springs, or a geothermal vent.

• Approx. Flavor Threshold:

  4µg/l

• Importance:

  Small quantities can give freshness to beer, but it quickly becomes an off flavor.

• Effect of Aging:

  May increase during maturation.

• Caused By:

  All yeast strains produce some amount of hydrogen sulphide during fermentation, but production can be increased when yeast are stressed. Other possible causes are bacterial infection and yeast autolysis.

How To Avoid/Control:

• Give your beer enough time. Ale fermentations are vigorous and much of the hydrogen sulphide is scrubbed out by released C02. Lager yeasts will produce more H2S and the fermentation tends to be much mellower. If a lager fermentation is done, but still smells sulfury chances are it needs some more maturation time before bottling.
• Select your yeast strain with care. Ensure you cast enough healthy yeast and oxygenate the wort well. Consider using a yeast nutrient to up the zinc content in the wort.
• Get the beer off of the yeast cake and into a secondary as soon as fermentation is complete.
• Ensure your sanitation practices are up to snuff so that you can take bacterial contamination off the list of possible causes.

How To Practice:

Practicing perception of this off flavor can be done by adding sodium metabisulfite to a light lager. This is available in the form of Campden tablets for use in mead and wine brewing. Dissolve one campden tablet in an ounce of beer then add tiny measured amounts to the basic practice setup until you can smell and taste the change.

*Important Note: If you have a sulfite allergy or asthma, do not drink your doctored lager, but you can still work on your aroma perception.

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5. Caprylic (octanoic or caprylic acid)

• Perceived As:

  Goatish, tallow-like, vegetable oil, waxy, goat cheese

• Approx. Flavor Threshold:

  4-6 mg/l

• Importance:

  An off flavor at high concentrations, caprylic, is considered a positive flavor at lower levels in some long matured lagers and lambics.

• Effect of Aging:

  Perception may increase with age.

• Caused By:

  These fatty acids are produced by the metabolism of yeast during fermentation. Production is dependent on pH conditions. At lower pH levels perception increases.

How To Avoid/Control:

• Pitch enough healthy yeast and aerate your wort well.
• Get your beer off of the yeast cake and into a secondary as soon as fermentation is complete.
• Store beer at cool temperatures.

How To Practice:

Caprylic acid is sold as a health supplement, usually in a gel-tab form. I've never tried this, but it seems you could practice your perception of the Caprylic off-flavor by poking a hole in a gel-tab with a needle and carefully dosing your beer. Don't squeeze it, you'll likely get more than you want. Let the drops flow naturally, this gives you a smaller more measurable dose. Mix well. Compare to your control lager and continue to add until you smell and taste the off-flavor.

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6. Butyric (butyric acid)

• Perceived As:

  Rancidity, Baby vomit, cheesy, putrid, spoiled milk or butter

• Approx. Flavor Threshold:

  2-3mg/l

• Importance:

  Always considered an off flavor in beer.

• Effect of Aging:

  Can increase if packaged beer has (or gets) bacterial contamination.

• Caused By:

  Bacterial Infection of sugar syrups; or during wort production, sour mashes in aerobic conditions, or after packaging. Flavor becomes more prominent with a lowering of pH.

How To Avoid/Control:

• Sanitation is key to avoiding this horrid off flavor.
• Smell and taste syrups before using them to ensure they are not contaminated.
• Do not expose sour mashes to outside air and keep them above 90°F.

How To Practice:

You probably don't need or want to practice this one. Believe me, if you can smell or taste it you'll know what it is.

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7. Grainy/Husky

• Perceived As:

  Fresh wheat, grainy, harsh, "green", nutty, like raw grain

• Approx. Flavor Threshold:

  1-20 µg/l

• Importance:

  Usually considered an off flavor, but certain styles, such as malt-forward lagers, may have perceptible low levels.

• Effect of Aging:

  Tends to mellow with age.

• Caused By:

  Most often caused by the isobutyraldehyde in malt, but other aldehydes can supply the grainy character. Higher levels of these compounds are found in freshly made malt which has not gone through an appropriate rest phase before use. This character can emerge due to malts being to finely crushed, mashing for too long a time, sparging with water at too hot a temperature, or oversparging.

How To Avoid/Control:

• Ensure you don't over crush your grain.
• If making your own malt, give it 2-8 weeks of rest before use.
• Don't mash for more than 2 hours.
• Keep your sparge below 168°F and don't collect wort below around 1.008 specific gravity.
• Cold conditioning a beer can help get rid of some of its graininess.

How To Practice:

This is pretty recognizable to everyone. If you homebrew, you can brew a small batch of beer, purposely disregarding any of the avoidance steps above to get varying intensities of this grainy character.

Also, you can make a tea of over-crushed malt in boiling water. Once it has cooled, dose the basic practice setup with measured doses, compare with the control until you can perceive and identify the off-flavor. Don't forget to write down how your perceptions change as the flavor gets more intense.

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8. Banana (Isoamyl Acetate)

• Perceived As:

  Fruity, Estery, Bananas, Pear, Peardrops, nail polish-like at higher levels

• Approx. Flavor Threshold:

  1.4 mg/l

• Importance:

  This ester is present in all beer and plays a role in overall flavor. It is especially prominent in wheat beers.

• Effect of Aging:

  Tends to decrease with aging.

• Caused By:

  All esters are produced by the yeast during fermentation. Over production of Isoamyl Acetate is usually a result of stressed yeast.

How To Avoid/Control:

• Choose the appropriate yeast for the style.
• Aerate wort thoroughly before fermentation starts and avoid aerating after fermentation as begun.
• Pitch the right amount of healthy yeast.
• Maintain good temperature control.
• Higher temperatures will cause the production of more esters.
• If you brew a beer with a high level of Isoamyl Acetate, try aging it to decrease the ester.

How To Practice:

The complexity of an ester profile is hard to duplicate as a whole, but you could get some idea of the isoamyl acetate flavor by using banana extract in the basic practice guidelines. As always have a control lager for compression.

Commercial Example: Most Bavarian Hefeweizens will have the distinct banana flavor.

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• Perceived As:

  Blood-like, Iron, Bitter, harsh, inky, rusty, coppery

• Approx. Flavor Threshold:

  1-1.5 mg/l

• Importance:

  Always an off-flavor. At a certain point metallic ions can also contribute to haze, stale flavors, and affect head quality. Can be toxic to yeast at high levels.

• Effect of Aging:

  Metallic notes will increase with age.

• Caused By:

  This flavor are caused by contact with metal materials during the brewing process, which leach metallic ions, and/or by lipid oxidation. Another possible contributor is brewing with water containing high levels of metallic ions.

How To Avoid/Control:

• Treat your brewing water to remove these ions or find a different source.
• Use food grade plastic, glass, or stainless steel to store both your fermenting and finished beer.
• Avoid any containers and fittings that may corrode and ensure you do not leave any type of caustic cleaner in contact with metal fittings or containers.

How To Practice:

We've all had a cut in our mouth or a bloody nose at some point so you'll have some idea what this tastes like. To practice, you can open a chilled macro lager pour it into a glass with a small piece of (cleaned) iron or copper pipe. Let it sit for about 30 seconds, then pull it out and see if you can smell and taste metallic notes. If not, drop it back in for an additional time period. Do this incrementally until you can perceive the off flavor.

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10. Sour

• Perceived As:

  Tart, Sour Milk, Acidic, Citrusy. At higher levels may give a peppery, almost burning mouthfeel.

• Approx. Flavor Threshold:

  170 mg/l

• Importance:

  All beers are acidic to some degree, but it becomes an off flavor if it is at too high a level overall or too high for a given style. Sourness at different levels can be appropriate to dry stouts, Belgian sours, Berliner weisse, Fruit beers, Goses, Witbier, and Wild Ales.

• Effect of Aging:

  May increase or decrease depending on the cause.

• Caused By:

  Any perceived sourness is due to added acids in the form of raw materials (i.e. fruit), fermentation, and/or bacterial contamination or inoculation. Yeast contributes some natural acids during fermentation. It can also be caused by certain brewing practices.

How To Avoid/Control:

• Practice proper sanitation.
• Choose a yeast strain appropriate to the style.
• Don't mash for longer than two hours.
• Pitch the right amount of healthy yeast to minimize lag time.
• Avoid high temperature fermentations.
• Don't contaminate your siphon by sucking to start the flow, instead use an auto-siphon.
• Replace plastic brewing supplies and equipment, especially fermentors, when they become scratched. Scratches can hide bacteria. Alternatively, use glass carboys or stainless steel.
• Limit acidic fruit and additions of acidulated malt and lactic acid.
• If sour mashing, avoid oxygenating and keep it above 130°F.

How To Practice:

Using the basic practice guidelines you could add tiny measured amounts of:

• Lemon extract for citric acid.
• White vinegar for acetic acid.
• Ascorbic acid to get a citrusy (solvent-like at higher levels) quality.
• Malic acid to create cidery sourness.

Commercial Examples: Try any of the above named beer styles to get an idea of the wide range of appropriate souring levels in given styles.

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11. Catty (p-menthane-8-thiol-3-one)

• Perceived As:

  Tomcat urine, catty, black currant leaves, tomato plants

• Approx. Flavor Threshold:

  15ng/l

• Importance:

  Catty is usually considered an off flavor, but can make up an important part of some ales, — especially IPAs — because the compound p-menthane-8-thiol-3-one is associated with the flavor and is produced by several hop varieties. It is also often present in the early stages of oxidation. If present because of oxidation it is always considered an off-flavor.

• Effect of Aging:

  Increases with age to a point; than begins to decrease.

• Caused By:

  It is caused by contamination of raw materials, or raw materials (hops) naturally producing the compounds that bring about this flavor.

How To Avoid/Control:

• Brew with different hop varieties that don't produce the catty compounds.
• Ensure your malt is clean.
• Minimize oxidation of wort or young beer.
• Store beer properly at cool temperatures.

How To Practice:

You could brew a small batch IPA with hop varieties known for their "cattiness;" Citra, Simcoe, and Strisselspalt are a few. You could also dose your basic practice setup with blackcurrant leaf extract or blackcurrant leaf tea. This is another I haven't personally tried, but it's worth looking into.

Commercial Example: Odell's IPA is a commercial example that has a strong catty character as part of its flavor profile.

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12. Cheesy (Isovaleric Acid)

• Perceived As:

  Old cheese, rancidity, old hops, goaty, dirty socks, sweaty

• Approx. Flavor Threshold:

  0.7 – 1 mg/l

• Importance:

  A "sometimes" component of some highly hopped beer styles, but in general is considered an off flavor.

• Effect of Aging:

  Will mellow with age.

• Caused By:

  A result of oxidation of the alpha acids in hops and may be confused with caprylic. If associated with alpha acids, it is often accompanied by grassy notes, but it can also be caused by bacterial infection.

How To Avoid/Control:

• Use fresh hops; ensure you buy fresh hops that have been stored correctly.
• Store hops in a freezer in a oxygen free, vacuum sealed container.
• Age beer that has cheesy notes to help mellow those flavors.
• Use good sanitation practices.

How To Practice:

You could practice this by making a hop tea with old mistreated hops then add measured amounts into the basic practice guidelines.

You could also brew a small batch beer with the old hops.

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13. Sweet

• Perceived As:

  Cloying, sickly sweet, oversweet, syrupy, jammy, candy

• Approx. Flavor Threshold:

  Varies

• Importance:

  Makes up some part of the character of every beer and is indicative of the presence of simple sugars left unfermented. It is only an off flavor when its level is too high for the style.

• Effect of Aging:

  Generally increases with age.

• Caused By:

  Excessive sweetness is often caused by poor fermentation and, in turn, poor yeast health. This can be due to high alcohol, uncontrolled fermentation temperature, poor yeast nutrient availability, or low levels of dissolved oxygen.

How To Avoid/Control:

• Reduce the use of non-fermentable sugars and use more simple sugars such as honey, corn sugar, or maple syrup.
• Mash at 142-149°F to increase fermentable sugars.
• Make a good yeast choice for the style and gravity.
• Pitch the right amount of healthy yeast for your wort's gravity.
• Supplement yeast nutrient.
• Enthusiastically aerate your wort before fermentation begins.
• Practice good fermentation temperature control.
• Pitch more yeast if needed.

If you want to increase sweetness:

• Mash at 150-156°F to increase the unfermentable sugars.
• Add non-fermentable sugars like dextrose.

How To Practice:

This is another one that doesn't really need much practice, but you can always mix in measured amounts of different kinds of sugar into different beer styles to see when the sweetness becomes noticeable and excessive.

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14. Dimethyl Sulfide (DMS)

• Perceived As:

  Sweetcorn, Creamed Corn, Cabbage, Canned/Cooked Vegetables, Oysters Sea Vegetables, Tomato Sauce

• Approx. Flavor Threshold:

  0.025mg/l

• Importance:

  Considered an off flavor in most beer, but can play some role in the flavor profile of some pale lagers, German and American pilsners, and cream ales.

• Effect of Aging:

  Likely will decrease with age.

• Caused By:

  DMS comes from a sulfur-based organic compound (S-methyl methionine, or SMM) produced when grain germinates during the malting process. Six row lager malts and Pilsner malts have the highest levels of this compound. As do some adjunct grains such as corn. SMM changes to DMS during the boil. It can also come from wild yeast or bacterial contamination during fermentation.

How To Avoid/Control:

• Reduce use of pilsner malts, lager malts, and corn adjuncts.
• Higher moisture content in malt increases the SMM, so make sure you store your malt in a dry, cool place.
• Over-sparging can increase DMS.
• DMS is a volatile compound and the easiest way to get rid of it is to drive it off with a vigorous boil. Always use a big enough kettle to allow for an energetic boil without having to worry about boil over. And always leave the lid off!
• Ensure your vigorous boil is long enough. Boil for at least 60 minutes and, if using lager or pilsner malt, consider upping it to 90 minutes.
• Also try your best to crash cool your boiled wort as quickly as possible. DMS is produced at warm non-boiling temperatures, so you don't want to leave your wort in that temperature-range long.
• As always, practice good sanitation.

How To Practice:

To get some practice with this off flavor, get into the kitchen and cook up some canned corn. After it's cooked, strain the liquid off and set the corn aside. Maybe you can use it as a complementary side dish for dinner tonight. Take the strained liquid use it in tiny measured amounts with your basic practice setup. Compare to your control until you note the off flavor.

Commercial Example: Rolling Rock is a commercial beer that has DMS as part of its flavor profile.

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15. Acetaldehyde

• Perceived As:

  Bruised apples, green apples, squash-like, latex paint, rough, jolly rancher Often sweet apple esters and sourness is mistaken for this off-flavor.

• Approx. Flavor Threshold:

  5-15 mg/l

• Importance:

  It is present in all beers at some level. It is part of the flavor profile of certain styles, such as American lagers and Biere de Garde.

• Effect of Aging:

  Generally will increase with age; though this study showed a decrease under certain conditions.

• Caused By:

  It is produced by yeast during fermentation as a precursor to ethanol. Can also be caused by oxidation, where too much O2 exists in packaged beer, it can change ethanols back to acetaldehyde.

How To Avoid/Control:

• Pitch enough healthy yeast. Use proper fermentation temperature.
• Avoid aeration after fermentation has begun.
• With lagers, allow fermentation to finish at a slightly higher temperature.
• Condition at a slightly warmer temperature.
• Minimize O2 introduction during bottling.
• Use a diacetyl rest.
• Wait a couple days after fermentation is complete before racking off of yeast.
• Use sound sanitation practices.

How To Practice:

Green apple extract or flavoring will give your senses a little practice in spotting this off-flavor. It is available at most grocery stores, or here on Amazon. Add it in small measured amounts to the basic practice setup.

Commercial Example: Budweiser contains low levels of acetaldyhde as part of its flavor profile.

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16. Oxidation

*Oxidation could easily be broken down into several different off flavors, but here we will keep it general.

• Perceived As:

  Sherry-like, Papery, like cardboard, stale, oxidized, "old book". At low levels can have a inky, musty quality.

• Approx. Flavor Threshold:

  Depends on specific flavor

• Importance:

  This is a flavor associated with the aging process of beer. What qualities it takes on depends on the style of beer and what temperature the beer is stored at. Some flavors associated with oxidation are important components of an aged beer's profile, others, are always considered off flavors.

• Effect of Aging:

  Oxidation characteristics are very fluid. Some flavors will increase; some will increase then decrease or level off.

• Caused By:

  Oxidation is directly caused by aging. How fast and to what extent this process occurs is a result of oxygen conditions, storage temperatures, and a beer's ingredients. The more oxygen a beer is in contact with the faster and more severe the oxidation. Cooler storage temperatures slow the process. There is a marked increase in oxidation as storage temperature increases. Ingredients used in the beer can both inhibit or aid oxidation.

How To Avoid/Control:

• Minimize aeration of hot wort by avoiding splashing, spraying, or vigorously stirring.
• Do not aerate beer after fermentation starts.
• Work to get good hot and cold break separation.
• Don't leave more than 1 to 2 inches of head space when bottling.
• Use ant-oxidant bottle caps and cap on foam if possible.
• When possible, purge kegging equipment with CO2 before using.
• Keep beer below 50°F if cellaring.
• Don't age beer unless it's meant to be aged.

How To Practice:

It is hard to practice for all the different oxidation flavors because each beer will age in a slightly different way. But you can get some idea of these flavors by going out and buying two or three different broad styles of beer. An example could be a lager, an IPA, and a stout. Take three bottles of each. Store one bottle of each at 85°F, one each at between 60 and 50°F, and one in the refrigerator. The ones in the refrigerator are controls and will not change much. After a month or so, take each style out and sample them against the control to see if they've changed.

You may want to perform this practice again with differing styles, a wider range of temperatures, or a longer storage period.

You could also add oxygen by filling bottles to different levels with homebrew leaving them for a week, then tasting them. The same thing could be done with commercial examples by drinking them down to different levels, recaping them, storing for a week, and sampling.

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17. Phenolic

*This is another flavor that could easily be broken down into several different components, but we will just do an overview here.

• Perceived As:

  Bitter, spicy, herbal, drying, tea-like, clove-like, smoky, band-aid, medicinal.

• Approx. Flavor Threshold:

  0.05 – 0.55 mg/l

• Importance:

  This is usually considered an off-flavor, but can make up a small element of the character in stouts and other ales. They are also a major contributor in German wheat beers.

• Effect of Aging:

  Won't really increase or decrease, if it's in the beer it's generally there, at that level, for good.

• Caused By:

  Can be caused by wild or specialty yeasts, contaminations, Chlorophenol presence in tap water, chlorine sanitizers, and improper sparging technique.

How To Avoid/Control:

• Use yeasts that will produce fewer phenols.
• If brewing with tap water, be sure to filter it first.
• Either rinse well after using chlorine sanitizers or use non-chlorine sanitizers, such as Star San.
• Use pure yeast strains and take proper precautions to ovoid wild yeast contamination during fermentation.
• Don't over-crush your grain.
• Don't collect wort below 1.008 SG.
• Keep sparge above 6.0pH and temperature below 168°F.

How To Practice:

Using the "Basic Practice Guidelines" you could add small measured amounts of clove extract to get the spicy clove-like element, while adding Chloraseptic throat spray will give more of a medicinal flavor.

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18. Musty (2,4,6-tricholoroanisole)(TCA)

• Perceived As:

  Old cellar, damp, earthy, moldy, wine cork, mushroom-like, beet-like.

• Approx. Flavor Threshold:

  <10-25 ng/l

• Importance:

  Never appropriate. Is a signature of mold contamination and improper sanitization techniques.

• Effect of Aging:

  In contaminated beer, perception will likely increase with age. Time to dump.

• Caused By:

  This one is usually caused by mold or fungus contamination of raw materials or brewing equipment improperly sanitized and stored.

How To Avoid/Control:

• Always clean and sanitize equipment before and after use.
• Ensure porous equipment, such as plastic and wood, are dry before storing.
• Do not brew or transfer beer where mold is likely to be growing.
• Do not let brewing equipment touch surfaces that are damp and likely moldy.

How To Practice:

We probably all have a pretty good idea of what this one smells and tastes like. But, the next wine you open smell the cork; the next time you're in a cellar stop and pay attention to the damp smell.

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Main Takeaways About Off-Flavors

The main take away from this article is simple: Practice good sanitation and brewing practices and off flavors will not be an issue. Simple.

These are some of the most common off flavors, but there are many others. One of my sources for this article and a good reference for further knowledge is: The Complete Beer Fault Guide by Thomas Barnes, which can be downloaded here (PDF).

If you happen to have any experience with off-flavored beer or other good additives for home practice please leave it as a comment below, so that we all can learn from your misfortune and knowledge.

Cheers!

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Source: https://learn.kegerator.com/off-flavors-in-beer/

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