Today I’m starting a series on the off flavors that you can experience in beer. Sometimes, when you taste your home brew, or even a professional brew, something just seems not quite right. You might experience a weird, unpleasant aroma or taste that puts you off from that beer. There are a few off flavors and aromas that you can trace back to an issue with the beer itself as well as the brewing process. Today, we’re starting this series off with a pretty common one: Acetaldehyde
What Is It?
Acetaldehyde (pronounced ac-et-al-de-hyde) is a naturally occurring chemical produced when yeast ferments. During the fermentation process acetaldehyde is usually converted back into ethanol. If not enough yeast was pitched, this conversion can be stalled. Depending on the alcohol level of the beer being brewed, this can take a fairly long time.
Acetaldehyde generally tastes and smells like green apples. This aroma and taste can move to rotten apples as well as fresh pumpkin as well. All are generally signs of acetaldehyde being present.
How To Avoid It
The easiest way to avoid acetaldehyde is to make sure you pitch the proper amount of yeast at the beginning of the fermentation process. The second way is to make sure you let the beer fully ferment before finishing the fermentation step.
Using a yeast starter will help make sure you’re using enough yeast and that the yeast you’re pitching is high-quality. Using low quality, expired, or not enough yeast is a sure fire way to get acetaldehyde in your beer.
Unlike most off tastes we will be talking about in the future, acetaldehyde does NOT come from improper cleaning or sanitation with your equipment. This comes mainly from the fermentation process not finishing as it should.
So, if your beer has that green apple or fresh pumpkin taste, it probably didn’t have enough yeast to fully ferment or it was rushed. Either way, its an avoidable problem that when you experience once, you probably won’t let happen again.