In the coming weeks, we’ll highlight the major off flavors you might run across in your homebrewing. From green apples and butterscotch to adhesive bandages and skunks, we’ll give you the tips you need to reduce such unwanted unpleasantness. In this first article in the series, we take a look at acetaldehyde.
Acetaldehyde (CH3CHO) is a naturally occurring organic compound that is found in everything from ripe fruit to coffee. It is frequently described as having a tart flavor reminiscent of green apples, and the flavor of dry cider also comes to mind.
Brewers yeast produces acetaldehyde as an intermediate compound in the conversion of glucose to ethanol, so it’s found in every beer you make, at least during primary fermentation. However, in a healthy fermentation, the yeast fully converts the vast majority of this compound to alcohol so that any residual amount falls below the flavor threshold. If the fermentation is less than optimal, the conversion of acetaldehyde to alcohol may remain incomplete, and too much will remain in the final beer.