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What Are Off Flavors in Beer?
Truly the bane of every brewer’s existence, off flavors are defects in commercial beer and are especially common in homebrewing operations. You’ll hear the term bandied about on craft beer message boards or homebrewing forums, but what are these exactly? An “off flavor” is essentially an unintended (and often unpleasant) smell or taste resulting from mistakes in the brewing process. These can be caused by faulty equipment, a hostile environment for the brewing process or ingredients, or user error.
While off-flavors are an inevitability for any homebrewery, they’re also preventable. The first step is identifying the precise off-flavor, then isolating and correcting the cause for future batches. Here’s everything you need to know:
Common Beer Off Flavors and How to Identify Them
| Off Flavor | Description | Common Causes | Beer Style Where It May Be Acceptable |
|---|---|---|---|
| Diacetyl | Buttery, slick mouthfeel | Under-fermentation, infection | Some English Ales |
| Acetaldehyde | Green apple, raw pumpkin | Young beer, poor oxygen control | None |
| Phenols | Clove, band-aid, smoke | Wild yeast, poor sanitation | Some Belgian/Witbier |
| DMS | Cooked corn, vegetal | Incomplete boil, covered kettle | Some Lagers |
| Oxidation | Stale cardboard, sherry | O₂ exposure post-fermentation | Barleywine (some aging) |
| Sourness | Tart, vinegar | Infection | Sours only |
| Metallic | Tinny, blood-like | Equipment contamination | Never desirable |
Diacetyl
By far the most common off-flavor in beer, diacetyl is also the most controversial, as there’s a segment of the brewing community that actually embraces it.
What it tastes like: Buttered popcorn and butterscotch.
Causes: Specific yeast strains, (too low or too high) fermentation temperatures, and premature racking. Incomplete fermentation, stressed or unhealthy yeast, and premature cold crashing can all lead to diacetyl’s development.
Prevention/fix: Diacetyl rest (raising temperature near the end of fermentation) works exceptionally well in brewing lagers. Healthy yeast and a proper fermentation timeline can also prevent diacetyl or minimize the strength of the flavor. Always confirm a full fermentation before bottling.
Acetaldehyde
How it’s identified: A strong, tart, apple-like flavor that is reminiscent of latex paint or even pumpkin is the most notable sign.
Cause: Under-fermented or under-conditioned (too-young) beers often have acetaldehyde. Unhealthy or stressed yeast and premature packaging (incomplete fermentation) are other culprits.
Fix: Longer conditioning, ensuring full fermentation, tight temperature control, and proper yeast pitching rates are focus points for preventing acetaldehyde. Patience is key!
Phenolic Flavors (Clove, Band-Aid, Smoke)
Identification: Spicy clove flavors are often found in Belgian styles, but these can be medicinal or plastic-like and are unwanted in most beer styles.
Cause: The most common causes are specific wild yeast strains, chlorine in water, and unsanitized equipment.
Fix: Proper sanitation and cleaning of all equipment is of particular importance. You can also use filtered or dechlorinated water for smaller batches. Yeast health is also essential, so avoid reusing it too many times or overpitching.
DMS (Dimethyl Sulfide – Cooked Corn, Cabbage)
Identification: DMS will have a sweet or vegetal aroma reminiscent of corn or cabbage.
Causes: Inadequate boiling (DMS comes from S-methyl methionine in malt that’s not sufficiently boiled off) of the wort or slow cooling. DMS is more common in beers with Pilsner malt.
Fix: Bring the wort to a full boil and then quickly chill it. This requires proper equipment, including a sufficient heat source and a proper chiller.
Oxidation (Stale, Cardboard, Sherry)
Identification: Oxidation usually presents a flat, dull flavor that can taste of cardboard or stale wine.
Causes: Oxygen exposure after fermentation is the primary culprit, especially during transfer.
Fix: Invest in a closed transfer system if your budget allows. You can also purge kegs with CO₂ and seal all packaging immediately.
Unintentional Infection (Sourness or Vinegar-Like Flavors)
Identification: Unintended sour or vinegar flavors, along with an odd funk, are signs of infection, accompanied by a visible white film (pellicle).
Causes: Poor sanitation of equipment is the number 1 cause. Certain wild yeasts or bacteria on the fermenter or packaging equipment usually cause contamination.
Prevention: Meticulous sanitation of all equipment is paramount. For brewing multiple batches, always separate sour and clean gear and don’t reuse infected plastic equipment. Star San, Iodophor, or other no-rinse sanitizers are ideal for preventing the spread of infection-causing bacteria.
Metallic Flavors
Identification: A strong metal taste reminiscent of sucking on a penny. Blood-like flavors are also common.
Causes: Uncoated metals, such as aluminum in brewing equipment, or high iron content in water are common causes.
Fix: Always use stainless steel or food-safe brewing equipment. Test your water quality and filter or use RO water if metals are present.
How to Fix a Beer That Tastes Off
- Many off-flavors fade with aging (especially green apple, diacetyl). This won’t reverse the problem, but the intensity of the flavors will be easier to stomach.
- Cold crash a beer to halt infection activity. Drinking it young will be a more pleasant experience, as the off flavors will develop with time.
- Some flavors (especially oxidation, metallic) are irreversible. The lesson with these defects is prevention, so your focus will be on new batches.
- If the batch is safe, blend it with another batch to dilute it and lessen the strength of the off flavor.
- Use the infected batch for non-drinking activities, such as cooking. The alcohol and off flavors will be burned off with the heat.
- As a last resort, dump it… This is especially important for batches that are infected and unsafe for consumption.
How to Prevent Off Flavors in Future Batches
- Ingredients matter! Use fresh and high-quality malts and hops that are marked as not expired.
- Thoroughly clean and sanitize all equipment! If you’ve had issues with sour or infected flavors, focus on improving sanitation practices before your next batch.
- Carefully control fermentation temperature throughout this step, as this precaution prevents multiple off-flavors from forming.
- Use the appropriate yeast strain and pitch rates detailed in a recipe.
- Only oxygenate before fermentation.
- Avoid oxygen (at all costs) during post-fermentation.
- Boil properly with consistent temperatures and chill rapidly.
- Find out the quality of your water and address issues if needed. Chlorine or other chemicals in your water can affect the taste. If you have issues, filtered or bottled water can be helpful in brewing smaller batches.
- If it’s your own recipe, adjust it to address underlying issues causing off flavors. This can include the type of hops or factors like mash temperature.
Off-Flavors by Brewing Stage
| Brewing Stage | Possible Off-Flavors Introduced |
|---|---|
| Mashing | DMS (poor boil), tannins (over-sparging) |
| Boiling | DMS (covered boil), caramelization errors |
| Fermentation | Diacetyl, acetaldehyde, fusel alcohols |
| Packaging/Bottling | Oxidation, contamination, carbonation issues |
| Storage | Oxidation, lightstruck, staling |
When Is an Off Flavor Actually Style-Appropriate?
Fortunately, not all off-flavors are always “bad,” even if they’re unintended. Certain beer styles are compatible with what might be perceived as flaws in the beer. Here are a few examples:
- Diacetyl: English bitters and some malty lagers can carry the butterscotch with compatible flavors.
- Phenolics: Belgian ales, German wheat beers can hold this off flavor pretty well.
- Sourness: Lambic, Berliner Weisse are two intentionally sour beer styles.
- Oxidation: Some aged barleywines and old ales will taste better with time.
Final Thoughts: Trust Your Taste Buds
Addressing quality control issues is a daunting task for any brewer, but it is particularly challenging for beginners. But persistence is key, and knowledge will always go a long way. To ensure you have as many resources as possible, consider downloading our free Beer Off-Flavors Cheat Sheet or subscribing to our homebrewing newsletter below for valuable tips and tricks.
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