Phenolic compounds: Difference between revisions

Phenolic acids (such as [[ferulic acid]]) are always present in beer, but they typically have no direct flavor impact since their concentrations are well below flavor threshold.<ref name=wangas/><ref name=vanvan/><ref name=len/><ref name=habkos/><ref name=calcol/> However, they act as flavor precursors because they can be modified during [[brewing]] and/or [[fermentation]] to create much more potent flavor compounds, called volatile phenols.<ref name=wangas/><ref name=vanvan/><ref name=len/><ref name=vandel/> The aroma and flavor profile contributed by volatile phenols in a beer is influenced by not just by the concentrations of individual phenolic compounds, but also the relative amounts, the total concentration of phenolics, their interactions with other compounds, and variation among individuals for sensitivity to these compounds.<ref name=len/> The resulting flavors may be desirable, or they may be considered off-flavors depending on the beer style. Styles that intentionally feature volatile phenolic flavors include [[weissbier]], [[rauchbier]], [[saison]], and various Belgian beers such as [[witbier]], [[belgian tripel|tripel]], and [[traditional sour beer]]s.<ref name=vanvan/><ref name=len/><ref name=habkos/> In these styles, volatile phenols often impart pleasant spicy, clove-like, sweet, and vanilla-like flavor notes, although, at higher concentrations they may be also add unpleasant medicinal flavor notes.<ref name=wangas/><ref name=len/><ref name=habkos/><ref name=coljer/> The "black pepper" character often present in certain styles is considered a phenolic flavor, however the compounds responsible have not been identified.<ref name=len/> Depending on the yeast(s), other volatile phenols can be produced that contribute "funky" flavors such as barnyard, horsey, leathery, and smoky.<ref name=len/> ''[[Brettanomyces]]'' yeast is notable for creating these funky flavors.<ref name=coljer/> Since volatile phenols are mainly formed during fermentation, the choice of an appropriate [[yeast]] strain is the primary way to control the final volatile phenol character in beer.<ref name=len/><ref name=vanvan/><ref name=habkos/> Among yeast varieties, the so-called "phenolic off-flavor"-positive (POF+) strains are responsible for creating the volatile phenols.<ref name=len/><ref name=langra>Langos D, Granvogl M. [https://pubs.acs.org/doi/abs/10.1021/acs.jafc.5b05606 Studies on the simultaneous formation of aroma-active and toxicologically relevant vinyl aromatics from free phenolic acids during wheat beer brewing.] ''J Agric Food Chem.'' 2016;64(11):2325–2332.</ref> A "ferulic acid rest" during [[mashing]] may be useful to increase the level of the precursor if a high clove flavor (4-vinylguaiacol) level is desired.<ref name=len/> Apart from the desired phenolic aroma-active substances, the toxic compound [[styrene]] is formed via the same pathway.<ref name=wangas/><ref name=schwarz/> esterified ferulic acid is less susceptible than free ferulic acid to undergo thermal or bacterial decarboxylation leading to 4- vinyl guaiacol, a compound that imparts a negative spicyclove like flavour to beer.<ref name=szwpie/>