Off-Flavor of the Week: Estery

Esters represent a complex group of organic compounds that include such diverse members as butterfat, olive oil, isoamyl acetate, and butyric acid.

Dave Carpenter Nov 1, 2014 - 4 min read

Off-Flavor of the Week: Estery Primary Image

Esters represent a complex group of organic compounds that include such diverse members as butterfat, olive oil, isoamyl acetate (the major aromatic compound in bananas), and butyric acid (the major aromatic compound in vomit).

If your beer tastes of vomit, then it probably got infected somewhere along the way, and all hope is lost: Dump it and start over. But a beer that tastes of banana may be perfect, or it could be seriously flawed. While some characteristics (e.g., astringency) are almost always considered flaws, esters are flaws in some styles and essential components in others. The key is to know what you’re brewing and how much ester character, if any, is appropriate.

Esters are fermentation by-products that offer up fruity notes reminiscent of pears, bananas, bubblegum, anise, or even rose petals. In high concentrations, esters can acquire a heavy, undesirable solvent-like character. But fruit character might be very appropriate depending on the beer.

Let’s take a look at two extremes: the German Pils and the German Weißbier. When you sniff a well-made German Pilsener, you shouldn’t detect any esters whatsoever. You’ll pick up a good dose of noble hops, a bready Pils malt backbone, and perhaps a suggestion of sulfur. German Weißbier, on the other hand, is a showcase for isoamyl acetate, the compound that smells and tastes like bananas. It’s why a well-made Bavarian Hefeweizen reminds us of banana bread.

English ales are also typically estery, though rarely to the same degree as Weißbier. And Belgian ales usually pair fruity esters with spicy phenols (more on those in a later installment). Most American ales include a low level of ester character, but usually more in a supporting role than front and center. Significant esters would be out of place in an American IPA, for example, while English IPAs often exhibit some fruity notes.

Ester formation is largely a function of yeast strain, fermentation temperature, and pitch rate. So, if you find that your beer is richer in esters than you would prefer, you might consider the following:

  • Switching yeast strains, from London Ale to American Ale, for example.
  • Fermenting at a lower temperature. The higher the temperature, the more ester character your beer will display. If you’ve ever brewed a bubblegum bomb, this is in all likelihood your issue.
  • Revisiting your yeast pitching practices. Pitching significantly less yeast than is recommended and failing to introduce enough oxygen is all but guaranteed to get you more esters than you had planned for.

It bears repeating that esters are not always bad, and in many cases, a robust ester profile is very desirable. You can manipulate your beer’s ester profile by adjusting fermentation variables. Perhaps more than the other off-flavors, esters offer the homebrewer some wiggle room to experiment and select a threshold that he or she finds suitable.