Stale Flavors In Beer

Stale flavors in beer are perceived as sherry-like, old bread, wet cardboard and paper. Wet Cardboard is the most common descriptor for these off flavors.

Oxidation occurs in brewing when the wort, at temperatures above 80 degrees F (27 degrees C) is introduced to oxygen. The reaction is commonly called hot side aeration (HSA). During HSA, aldehydes are formed in the wort which will not be degraded by the boil and which remain in the finished beer. These aldehydes will result in the oxidative character described above as the beer is stored.

Oxidation is inevitable in all beers. For beers that are meant to be aged for a long time, such as barleywines, the flavors are akin to sherry or fig notes rather than the cardboard flavors and is not considered a fault.

To avoid oxidation and wet-cardboard flavors in your beers, avoid hot side aeration. Do not splash your wort while its temperature is above 80 degrees F (27 degrees C) during any stage of brewing. Stir slowly without splashing when cooling your wort with an immersion chiller. If you whirlpool your wort, design the system so that very little to no splashing occurs. This may involve adjusting the pump speed or the re-design of the copper pieces attached to your system or immersion chiller. Just remember that when the wort is warm or hot to the touch, avoid aerating the wort to keep HSA to a minimum.

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