Month: May 2009

This may be perceived in both the aroma and the taste and is reminiscent of the flavor of spent grains. Possible causes include overcrushing, oversparging or sparging with hot or alkaline water. Long mashes may also leach these flavors from the grain husks. Low levels are acceptable in some lagers, but are not appropriate in any ale.

This is the flavor and aroma of freshly cut grass or green leaves. Responsible compounds include the aldehydes hexanal and heptanal, which are produced by the oxidation of alcohols in the finished beer or the deterioration of improperly stored malt or hops. Some English and American hop varieties produce grassy notes if used in large quantities, but this flavor should not be a significant part of the profile.

This is an aroma and taste that recalls bananas, strawberries, pears, apples, plums, papaya and/or other fruits. The responsible compounds are esters, which are formed from the combination of an alcohol and an organic acid. High ester levels are a product of the yeast strain, fermentation temperature, high gravity worts and the metabolism of fatty acids in the trub. These flavors are desirable in most ales, particularly Belgian and British styles, and the signature banana notes in Bavarian wheat beers are primary due to the ester isoamyl acetate. Note that esters often have solvent notes at very high concentrations.

DMS, or dimethyl-sulfide produces the aroma and taste of cooked vegetables, notably corn, celery, cabbage or parsnips. In extreme cases, it may even be reminiscent of shellfish or water in which shrimp has been boiled. DMS is normally produced by the heat-induced conversion of S-methyl-methionine, but most of this evaporates during an open, rolling boil. A closed boil or slow cooling of the wort may therefore lead to abnormally high levels. Some DMS is also scrubbed out during a vigorous fermentation, which is why lagers and cold-conditioned ales may have slightly higher levels than warm-fermented ales. Wild yeast or Zymomonas bacteria may produce high enough levels of DMS to make the beer undrinkable. Low levels of DMS are appropriate in most lagers, particularly American light lagers and pre-prohibition pilsners, but are not desirable in any ale style.