"Ester" Flavor

[Yreval2]

I often hear descriptions of beers or yeasts (particularly Belgian styles) that have "ester" character. I'm a few years removed from college chemistry now—and it was never my forté—but aren't esters a pretty large, diverse group of chemicals? Even the odiferous esters common to "essential oils" are responsible for a wide gamut of smells, from raisins to wood glue.

I'm a little confused what people mean when they refer to the "ester" flavors of certain fermentations. Is this shorthand for a certain, specific family of esters? Or some different piece of vernacular that stuck for whatever reason?

 

[suregork]

Esters are formed by the yeast during fermentation through intracellular condensation reactions between alcohols and acyl-CoA, catalysed mainly by alcohol acetyltransferases (such as the enzymes encoded by ATF1, Lg-ATF1, and ATF2). The main esters formed during fermentation are the:
a) acetate esters (in which the acid group is derived from acetyl-CoA and the alcohol group is ethanol or a higher alcohol derived from amino acid metabolism)

Ethyl acetate (fruity, solvent)
3-Methylbutylacetate / isoamyl acetate (banana)
2-Phenylethylacetate (rose, honey)

b) ethyl esters (in which the acid group is a medium-chain fatty acid and the alcohol group is ethanol)

Ethyl caproate / ethyl hexanoate (apple, fruity)
Ethyl caprylate / ethyl octanoate (apple, aniseed)
Ethyl decanoate (floral)

These esters aren't formed in large amounts during fermentation (compared to other metabolic products), but they are still an important part of beer flavour because of their low odour thresholds. Isoamyl acetate is prominent in e.g. hefeweizens and many Belgian styles.

 

[Yreval2]

Perfect response! Thanks for the guidance.