Alcohols
Please check back later for additional changes
oxygen radicals are very reactive with ethanol, the second most abundant component in beer, leading to the formation of off-flavors and consequent beer deterioration (Andersen and Skibsted 1998; Andersen and others 2000; Vanderhaegen and others 2006).[1] hydroxyl radicals react mainly ethanol to produce 1-hydroxyethyl radicals.[2]
Alcohols in beer can be converted to their equivalent aldehydes through the mediation of melanoidins, with the oxidized carbonyl groups on the latter acting as electron acceptors ( Hashimoto, 1972a ). Devreux et al. (1981) suggest that the reaction is inhibited by polyphenols and requires light, so is of secondary signifi cance in beer. Meanwhile, Irwin et al. (1991) argue that the effi ciency of conversion is so small as to make the pathway irrelevant.[3]
Melanoidins are responsible for the oxidation of higher alcohols to volatile aldehydes, as reported by Hashimoto, leading to beer oxidation and deterioration. The mechanism involves the transference of electrons or hydrogen from alcohols to carbonyl groups of melanoidins in conditions of high temperature and low pH (Hashimoto 1972). The melanoidin-mediated oxidation of higher alcohols, associated with the oxidation of isohumolones and unsatured fatty acids, is responsible for the formation of volatile aldehydes with a negative impact in beer flavor and storage stability (Hashimoto 1977).[1]
In beer, the intermediate highly reactive hydroxyl radical reacts with ethanol to form the 1-hydroxylethyl radical.[4] The latter can either further oxidize to acetaldehyde or react with hop bitter acids to affect the beer flavor.
References[edit]
- ↑ a b Carvalho DO, Gonçalves LM, Guido LF. Overall antioxidant properties of malt and how they are influenced by the individual constituents of barley and the malting process. Compr Rev Food Sci Food Saf. 2016;15(5):927–943.
- ↑ Callemien D, Collin S. Structure, organoleptic properties, quantification methods, and stability of phenolic compounds in beer—a review. Food Rev Int. 2009;26(1):1–84.
- ↑ Bamforth CW, Lentini A. The flavor instability of beer. In: Bamforth CW, ed. Beer: A Quality Perspective. Academic Press; 2009:85–109.
- ↑ Pagenstecher M, Maia C, Andersen ML. Retention of iron and copper during mashing of roasted malts. J Am Soc Brew Chem. 2021;79(2):138–144.