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The Most Common Lager Off-flavors and How To Control Them
Lager is a beer style where imperfections have nowhere to hide. Unlike more robust styles that can mask minor flaws with bold flavors, lager’s delicate balance and subtle nuances make it exceptionally vulnerable to off-flavors. These unwanted tastes and aromas can completely derail the intended drinking experience, transforming a refreshing and enjoyable beer into something unpleasant.
DMS
Contributes a cooked corn or cabbage aroma to beer. It is produced when S-methylmethionine (SMM), a compound found in malt (especially in lightly kilned malt), is heated during the boiling process.
To minimize DMS:
- Select high quality malts with low SMM concentrations.
- Boil vigorously for 60 to 90 minutes.
- Ensure adequate kettle ventilation.
- Avoid acid additions at the start of boil.
- Cool the wort rapidly after boil.
Acetaldehyde
Green apple flavors, sometimes with cidery or vinegary hints, are indicative of excess acetaldehyde in beer. While a natural fermentation byproduct, acetaldehyde is normally present at levels too low to detect. Higher concentrations suggest a fermentation issue, often stemming from incomplete fermentation or yeast stress, such as over-aeration, fermentation under pressure, or excessively warm temperatures.
To minimize acetaldehyde:
- Ensure only healthy, vital yeast is used.
- Use the appropriate pitch rate, fermentation temperature, and aeration for the selected yeast strain.
- Avoid premature yeast flocculation. A good diacetyl management strategy will generally result in lower levels of acetaldehyde.
Diacetyl
A naturally occurring byproduct of yeast fermentation, diacetyl imparts a buttery or butterscotch flavor to beer. While acceptable in some styles like English ales, it is considered an off-flavor in lagers. Diacetyl is formed when yeast produces acetolactate, which then spontaneously and non-enzymatically degrades into diacetyl. It may then be reabsorbed by the yeast and further reduced to acetoin, a flavorless compound.
To minimize diacetyl:
- Ensure sufficient wort nutrition. FAN levels can be increased by performing a protein rest, adding a neutral protease enzyme and adding nutrients.
- Select a yeast strain that produces lower levels of diacetyl.
- Ensure an adequate pitching rate of highly viable yeast.
- Perform a diacetyl rest at the end of fermentation.
- Give the beer sufficient contact time with the active yeast prior to transfer.
- Use an acetolactate decarboxylase enzyme (ALDC) to prevent diacetyl formation.
H₂S
The flavor of boiled or rotten eggs in beer is a sign of hydrogen sulfide (H₂S), a highly volatile compound produced by normal yeast metabolism when sulfate ions are reduced for processing into amino acids. Yeast will reabsorb H₂S at the end of fermentation, resulting in a decrease in H₂S levels in the beer.
To minimize H₂S:
- Ensure an adequate pitch rate of healthy yeast.
- Use a balanced nutrient containing nitrogen, vitamins, and minerals.
- Give the beer sufficient contact time with the yeast at the end of fermentation.
- Avoid contact with oxygen in late stages or after fermentation is complete.
- Use a product containing copper to remove H₂S from finished beer.
Papery
Trans-2-nonenal is an aldehyde responsible for papery or cardboard-like flavors in beer. It is formed by the oxidation of fatty acids released by lipase and lipoxygenase enzymes during mashing. As beer ages, this reaction is accelerated by heat in the presence of oxygen.
To minimize trans-2-nonenal:
- Avoid aerating brewing water, mash, wort and beer.
- Purge hoses, pipes and tanks with CO₂.
- Store packaged beer at lower temperatures.
- Consider using commercially available antioxidants.
Light Struck
Lightstruck flavor, often described as skunky, is a common off-flavor for light lagers. It occurs when beer is exposed to light, particularly ultraviolet (UV) rays. These rays cause a chemical reaction between hop-derived iso-alpha acids and sulfur compounds, creating the skunky-smelling compound 3-methyl-2-butene-1-thiol (MBT).
To minimize MBT:
- Use brown bottles, or ideally – cans. These types of packaging offer protection against UV light and therefore prevent the formation of MBT.
- Use modified or reduced iso-alpha acids, which make beer non-reactive to light.
Understanding the origins of these off-flavors and implementing preventative measures is crucial for any brewer, whether home or commercial, striving to craft exceptional lagers. Some of the mentioned off-flavors may also be produced by specific bacteria or wild yeast, so following best practices for sanitation is essential.
Detecting these off-flavors in your beer is the first step in preventing them. The Siebel Institute provides additional information about sensory training for off-flavors.
Published Apr 15, 2025 | Updated Apr 16, 2025