Tuesday Beer Trivia: Off-Flavors

Question 1: Movie popcorn, butter and butterscotch are all tell-tale signs of diacetyl. Diacetyl is detectable in both flavor and aroma. While it is sometimes pleasant at very low levels in some English styles, it is typically considered an undesirable off-flavor. Most often, stressed yeast leak diacetyl during amino acid synthesis causing the butter popcorn characteristic, but it can also be a sign of bacterial infection from things like dirty keg lines.

Learn more about diacetyl and how to prevent it.

Question 2: Beer that has been oxidized can have aromas and flavors reminiscent of cardboard, wet paper or just a general “stale” characteristic. While oxidation can sometimes take the form of sweet and sherry-like qualities, adding depth to styles like barley wine or old ale, it is rarely a desired trait in beer. Unfortunately, once oxidation occurs it is unable to be fixed, but steps can be taken to prevent if from happening in your next homebrew.

Learn more about oxidation and how to prevent it.

Question 3: Metallic qualities similar to coins, iron or blood, are typically categorized as flavor flaws, but they are often detected as aromas and sensations on the palate. This off-flavor is never a preferable quality in beer. Typically, tasting metallic qualities is a sign that unprotected metals were dissolved into the wort, or your brewing water source has high levels of things like iron or copper. This is not always a terrible thing from a nutritional standpoint, but it is less than pleasant as a detectable characteristic in beer.

Learn more about metallic off-flavors and how to prevent them.

Question 4: Acetaldehyde is a key signifier of young (also known as “green”) beer, which comes across as fresh cut green apples or cider-like. Often you just need to allow beer to condition longer, sometimes while still in contact with yeast. “Krausening” is the technique of adding wort that is undergoing high fermentation activity to introduce yeast into the beer that can help “clean up” the acetaldehyde.

Learn more about acetaldehyde and how to prevent it.

Question 5: Creamed corn, cabbage, green beans, canned asparagus and even tomato juice (typically in darker beers) can be a sign of dimethyl sulfide, more commonly referred to by homebrewers as DMS. The aromatic off-flavor is typically never considered favorable in beer, but in small amounts it can be acceptable in lagers. In shortened terms, DMS is created when S-methyl-methionine (SMM)—a compound typically reduced in malt during the roasting/toasting process—is reduced during the boil. Malts that have a higher degree of roast have less available SMM, meaning less DMS production in the boil, which is why DMS is very common in light lagers. In other instances where the DMS is found in exceptionally high levels, the cause can be due to bacterial infection.

Learn more about DMS and how to prevent it.

Question 6: Skunky and rubbery flavors or aromas in homebrew can be signs of “light-struck” homebrew. This quality is typically never desired in any style of beer. Beer becomes light-struck when the isohumulone bittering compounds in hops come into contact and react with specific wavelengths of light. Skunky aroma can also be caused by using Cluster hops for late boil additions. To prevent light-stricken beer in the future, use brown bottles when packaging and store bottles out of the light. In some instances, the reaction can occur  in a matter of seconds, resulting in an undesirable skunky off-flavor.

Learn more about light-struck beer and how to prevent it.