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Learning to Taste: Acetaldehyde

Acetaldehyde is a compound found in beers that had a poorly managed fermentation. You’d never want to have this off-flavor in your beer, and you’ll recognize it by its signature green apple flavors (if green had a flavor, this would be it). It’s a simple to recognize compound, but in order to understand what it is, we have to discuss a few fermentation basics.

When brewers produce beer, they first create a sugary liquid called wort. Yeast, a single-celled organism, is added to the wort; they eat up the sugars, and produce alcohol and carbon dioxide along with a bunch of other things. One of these other byproducts is acetaldehyde, and it’s created when yeast remove carbon dioxide from their bodies. Eventually, yeast will reabsorb the acetaldehyde but only towards the end of the fermentation process. If the brewer doesn’t allow fermentation to finish completely, you’ll be sure to taste it.

The classic acetaldehyde flavor is green apple, and it’s a flavor you’ll be able to smell and taste. However, green apples aren’t the only flavor associated with this compound. A lot of people say that they taste wet grass, raw pumpkin, avocado, and even latex paint. While some of these descriptions sound nice, they don’t play well with beer. They can give beer a vinegary flavor that will distract you from what the brewer intended you to taste and make the beer a one dimensional mess. While it sounds pretty bad, brewers can easily avoid this flaw through proper fermentation.

As a by-product of an immature or poorly managed fermentation, acetaldehyde can be managed with two easy measures: let the beer finish fermenting and use the right amount of yeast. Brewers have tools, formulas, and calculators at their disposal that help them determine how far along the fermentation process a beer is and calculate the correct amount of yeast to use for each beer. Using the right tools and techniques will (in almost all cases) eliminate acetaldehyde issues, and the simplicity of the solution makes you question the quality of a brewery that sells beer tainted with green apple flavors.

Beers with a rushed or incomplete fermentation will often develop acetaldehyde problems. These problems result in the beer tasting like green apples and lawn mower clippings; however, brewers can simply avoid those off flavors by allowing the yeast to do its job in the fermentor.


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