Aldehydes
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Aldehydes are the immediate oxidation products of alcohols, and the formation of aldehydes is concomitant with an oxidation process in aging beer and wine.[1]
Excess FAN in beer can increase stale taste from furfural production during aging via the Maillard reaction; furfural is a compound causing "biscuits", "caramel", and "burnt", and fruity aged or vinous character.[2]
The formation of long-chain staling aldehydes and precursors during malting and mashing is believed to be the main mechanism implicated in causing stale and off-flavors in beer.[3]
Grainy/Husky reminds one of raw grain, fresh wheat, grainy, harsh, “green,” nutty flavors, which are comparable to astringency from tannins and/or oxidization. It can be perceived at 1–20 µg/L. The emergence of this off-flavor is mostly caused by the isobutyraldehyde in malt, but other aldehydes can impart the grainy character, and higher levels of these compounds are found in freshly made malt if it was not subjected to an appropriate rest phase before use. This off-flavor can also appear if malt has been crushed too finely, mashed for too long, sparged with water at too hot a temperature, or oversparged [132,133,134].[4]
The formation of aldehydes during fermentation is bound up to the formation of higher alcohols, but they result to be more flavour active than their corresponding aldehydes. Generally they are considered to contribute negative flavour attributes to beer. Concentrations of aldehydes and ketones in beer are comparatively low respect to the other volatiles: acetaldehyde is the predominant compound, usually at no more than 10 ppm. The methylbutanals are among the most important Strecker aldehydes. Originated by the degradation of amino acids they are considered contributors to aroma, considered to be responsible for the malty character (Soares Da Costa et al. 2004). Diacetyl is produced as a byproduct of fermentation and its concentration is often used as an index of the completion of beer fermentation or maturation (Petersen et al. 2004). At high concentrations ([ 0.1 ppm), diacetyl may bring buttery/solvent like flavour and a rancid mouthfeel to the beer. Although for some beer styles, like stouts, scotch ales and pilsners, diacetyl concentration slightly above the threshold (0.15 mg/L) is accepted, and it brings a toffee-like described flavour (Vieira Humia et al. 2019).[5]
aldehydes can be classified into Strecker degradation aldehydes (2-methylpropanal, 2- and 3-methylbutanal, methional, and phenylacetaldehyde), aldehydes formed during Maillard reactions (furfural) and lipid oxidation aldehydes (hexanal and trans-2-nonenal).[6]
References[edit]
- ↑ Irwin AJ, Barker RL, Pipasts P. The Role of Copper, Oxygen, and Polyphenols in Beer Flavor Instability. J Am Soc Brew Chem. 1991;49(3):140–149.
- ↑ Lund MN, Petersen MA, Andersen ML, Lunde C. Effect of protease treatment during mashing on protein-derived thiol content and flavor stability of beer during storage. J Am Soc Brew Chem. 2015;73(3):287–295.
- ↑ Guido LF, Boivin P, Benismail N, Gonçalves CR, Barros AA. An early development of the nonenal potential in the malting process. Eur Food Res Technol. 2005;220:200–206.
- ↑ Habschied K, Košir IJ, Krstanović V, Kumrić G, Mastanjević K. Beer polyphenols—bitterness, astringency, and off-flavors. Beverages. 2021;7(2):38.
- ↑ Liguori L, De Francesco G, Orilio P, Perretti G, Albanese D. Influence of malt composition on the quality of a top fermented beer. J Food Sci Technol. 2021;58:2295–2303.
- ↑ Ditrych M, Filipowska W, De Rouck G, et al. Investigating the evolution of free staling aldehydes throughout the wort production process. BrewingScience. 2019;72(Jan/Feb):10–17.