13,602
edits
Changes
added methional to "Other flavors"
''Cover lifespan and effects of THP (reference THP page), diacetyl, proteins, enzymes, gluten(?), effects of different levels of CO2.''
Several volatile [https://en.wikipedia.org/wiki/Carbonyl_group carbonyl compounds] are formed during beer aging. Acetaldehyde is one such major flavor compound formed during aging and one of the first documented in science. The aldehyde trans-2-nonenal is the compound responsible for the cardboard (also described as "lipstick") flavor in aged beers and was once thought of as ''the'' molecule responsible for beer staling. This interpretation was updated by studies by Van Eerde et al. and Narziss et al. where it was shown that trans-2-nonenal formation was dependent on temperature (a lot is formed at 40°C, but none is formed at 20°C), and other authors observed that trans-2-nonenal develops independently of dissolved oxygen. Carbonyl scavengers such as [https://en.wikipedia.org/wiki/Hydroxylamine hydroxylamine] might help to diminish the effects of carbonyl staling compounds such as trans-2-nonenal. Other aldehydes known as "strecker" aldehydes are formed during beer storage and increase depending on oxygen. While many of them are not impactful on flavor, their presence is indicative of an oxidation issue <ref name="Vanderhaegen_2006" />. One such aldehyde that impacts the flavor of aging beer is the malt derived compound, methional. Methional is formed by the degradation of methionine by oxidation. The flavor of methional is described as "mashed potato" or "potato chips", and is common in wheat based beers <ref name="hall_mitchell">[http://pubs.acs.org/doi/full/10.1021/jf049178l Further Insights into the Role of Methional and Phenylacetaldehyde in Lager Beer Flavor Stability. M. Soares da Costa, C. Gonçalves, A. Ferreira, C. Ibsen, P. Guedes de Pinho, and A. C. Silva Ferreira. 2004.]</ref><ref>[https://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars Robert Hall, Andy Mitchell. Beer Oxidation: Chemistry, Sensory Evaluation, and Prevention. HomebrewCon 2017 Seminar. 2017.]</ref>.
Ketones are also formed during the storage of bottled beer. Beta-damascenone (rhubarb, red fruits, strawberry, floral) can be formed from hops, as well as 3-methyl-butan-2-one and 4-methylpentan-2-one. The buttery tasting compounds diacetyl and 2,3-pentanedione are also formed during beer aging. These are more pronounced in beers that have higher dissolved oxygen during packaging. Diacetyl, in particular, can form levels that are above flavor threshold. In the case of damascenone, it was found to increase greatly in aged beer that was at a pH of 3 or 4.2 versus a higher pH. This was attributed to the acidic hydrolysis of glycosides. The release of flavor compounds from glycosides could be present in acidic beers that are aged on fruit or herbs <ref name="Vanderhaegen_2006" />. See [[Glycosides#Acidic_Hydrolysis|Glycosides]] for more information.