Glossary
Ester
Fruity aroma compounds produced by yeast during fermentation — banana, pear, apple, rose and red fruit — as distinct from fruit character that comes from hops.
Also called esters, estery, isoamyl acetate, ethyl acetate.
Esters form when yeast combines alcohols with acids, and production rises with fermentation temperature, with under-pitching and with wort gravity. This is why the same strain gives a clean beer at 18 °C and a banana-forward one at 24 °C.
Isoamyl acetate is the banana note that defines a Bavarian Hefeweizen; ethyl acetate at low levels is fruity and pear-like and at high levels reads as solvent or nail varnish. Whether esters are welcome is entirely a question of style: essential in a weissbier, a defect in a pilsner.
Related
- Phenol — The other main yeast-derived flavour class.
- Fermentation — Where esters are made.
- Weissbier — The style built on a specific ester.
More vocabulary
Astringency · Body · Chill haze · Head retention · Hop burn · Lacing · Mouthfeel · Phenol
See every term on the glossary index.
Last reviewed 2026-08-16.
Evidence
What BeerHQ knows about this, and how. Every statement carries the state of the evidence behind it rather than being presented flatly as fact.
Esters are assembled by yeast enzymes rather than appearing spontaneously: acetyltransferases join acetyl coenzyme A to an alcohol, and higher fermentation temperature or wort gravity increases how much of them a fermentation makes.
Checked against the source
Sources: Lilly et al., "Effect of Increased Yeast Alcohol Acetyltransferase Activity on Flavor Profiles of Wine and Distillates" (2000), abstract and introduction (Appl Environ Microbiol 66(2):744–753); Svedlund et al., "Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation" (2022), section on acetylation of 3-mercaptohexanol (Appl Microbiol Biotechnol 106(13–16):4929–4944)