« on: February 01, 2011, 06:09:36 PM »
If it is acetylaldehyde, that should go away with time. You may try warming up some bottles for a couple days at room temp and see if this helps it go away.
Per the BJCP exam site:
This compound has the taste and aroma of fresh-cut green apples, and has also been compared to grass, green leaves and latex paint. It is normally reduced to ethanol by yeast during the secondary fermentation, but oxidation of the finished beer may reverse this process, converting ethanol to acetaldehyde. Elevated levels are generally present in green beer or if the beer is prematurely removed from the yeast. It can also be a product of bacterial spoilage by Zymomonas or Acetobacter. Background levels of acetaldehyde can be tasted in Budweiser due to the use of beechwood chips to drop the yeast before it can be reduced to ethanol.
This can also be the result of inadequate wort oxygenation, though the resultant yeast byproducts are normally metabolic intermediates they can remain after fermentation in some cases.
This compound is responsible for an artificial butter, butterscotch or toffee-like aroma and taste. At low levels, it may also produce a slickness on the palate. A significant number of tasters cannot perceive diacetyl at any concentration, so every judge should be aware of his or her limitations. Diacetyl is a fermentation by-product which is normally absorbed by the yeast and reduced to more innocuous diols. High levels can result from prematurely separating the beer from the yeast or by exposure to oxygen during the fermentation. Low FAN levels or mutation may also inhibit the ability of yeast to reduce diacetyl. Note that high fermentation temperatures promote both the formation and elimination of diacetyl, but the latter is more effective. For that reason, lager breweries often employ a diacetyl rest, which involves holding the beer in the 60-65 °F range for a few days after racking to the conditioning tank. Diacetyl is also produced by lactic acid bacteria, notably Pediococcus damnosus. Low levels of diacetyl are permissible in nearly all ales, particularly those brewed in the United Kingdom, and even some lagers, notably Czech pilseners.
Though rarely used by homebrewers, kräusening is a technique that can be used to eliminate diacetyl in beer. The technique works because of the introduction of fresh yeast that is actively multiplying and is thus able to rapidly remove diacetyl.
Hope this helps. Let us know how it turns out.