Beer Fact Friday: Esters
Fruity flavors in beer can arise from a variety of ingredients. Actual fruit is the most obvious culprit; today you’ll find all manner of beers brewed or aged with watermelons, cherries, grapefruits, and otherwise. Hops, as we’ve discussed in previous BFFs, can also contain oils and terpenes that mimic the aroma of citrus or tropical fruit. But today we’re talking esters, the largest group of flavor compounds in beer. And those, friends, are produced by yeast.
As yeast do the hard, essential work of fermenting beer, they produce alcohol and organic acids, which sometimes combine to form entirely new compounds. We call these compounds esters. (The common ester ethyl acetate, for example, arises as a result of a reaction between ethanol and acetic acid.) The banana-like flavor you get from a glass of Hefeweizen or the whiff of pears you pick up when sniffing a Belgian Tripel are purely the product of esters produced by yeast.
Here are a few of the most common esters and the fruit flavors they mimic:
- Ethyl Acetate: generic “fruity” character; can be solvent (like nail polish) at high levels
- Ethyl Butyrate: pineapple
- Ethyl Caproate: apple, aniseed, apricot
- Ethyl Caprylate: apple, pineapple
- Isoamyl Acetate: banana, peardrop
- Phenylethyl Acetate: roses, honey
Nearly 100 different esters have been found to occur in beer. The levels of each ester can be affected by a number of factors, including the composition of the wort (i.e. oxygen, nitrogen, and sugar levels), fermentation conditions (such as temperature and the geometry of the fermentation tank), and by the yeast strain itself (some strains are known—or bred—to produce higher levels of certain esters).
Our house yeast strain tends to produce an ester that smells like apricots; see if you can pick it up the next time you give Kilt Lifter a sniff.
Beer Fact Friday is our weekly exploration of the topics that make beer the world’s most interesting beverage. Check back here next week—or follow us on Facebook, Instagram, or Twitter—for more fascinating beer trivia.