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June 20, 2022
Last updated

How to Fix Bad Beer | Removing Acetaldehyde From Homebrew

Owner of Clawhammer Supply
How to Fix Bad Beer - Removing Acetaldehyde from HomebrewAcetaldehyde is a common off-flavor in beer that tastes like green apples. Needless to say, it’s not a desired flavor. We recently brewed a West Coast IPA that tasted sweet and tart, like a green apple, instead of bitter and dank. We knew Acetaldehyde was causing this, so we came up with a quick and easy strategy to remove this common off-flavor. Learn what causes Acetaldehyde and how to remove it from your beer below!

Full How-To Video

Watch us remove Acetaldehyde from a West Coast IPA in the video below.

How Is Acetaldehyde Caused?

Acetaldehyde is a natural byproduct of fermentation, but if fermentation finishes completely the yeast naturally cleans up this off-flavor. Acetaldehyde is caused when fermentation does not fully complete. Below are some reasons why this may happen.

  • Not pitching enough yeast
  • Not aerating your wort before fermentation
  • Racking the beer into a keg before fermentation is complete
  • Fermenting your beer at incorrect temperatures

We believe our West Coast IPA tasted like Acetaldehyde because we racked it into a keg too soon. 

How to Remove Acetaldehyde From Beer

In order to remove this green apple flavor from our beer, we came up with the strategy of making a yeast starter and adding actively fermenting wort to the beer. This will kick off fermentation in our beer again and the yeast will clean up any acetaldehyde.

To learn how to make a yeast starter, read this article here or watch the video above. Please note that we did two things differently when making a yeast starter for this project. Instead of putting our scientific flask directly on a hot plate, we put it in a pot of boiling water. Putting a flask directly on a burner can stress the glass and cause it to break. We also did not use a foam stopper to cover the top of the flask. Instead, we used a small sanitized bowl and placed it upside down over the opening of the flask. A foam stopper or a sanitized bowl both work fine.

Once you’ve made your yeast starter, open up your beer that tastes like acetaldehyde and pitch the yeast starter into the beer. Seal the beer back up and let it ferment for 10 days.


Our strategy worked! Once we tasted our beer after 10 days, the apple flavor was gone! However, the hop flavor and aroma had almost completely disappeared. If you’re trying this strategy with an IPA like us, we recommend dry hopping for 2-3 days after fermentation has completed again.

Kyle Brown is the owner of Clawhammer Supply, a small scale distillation and brewing equipment company which he founded in 2009. His passion is teaching people about the many uses of distillation equipment as well as how to make beer at home. When he isn't brewing beer or writing about it, you can find him at his local gym or on the running trail.

  • Hi, i live in Philippines a beginer, practicing brewing beer at home. I always watch guys to get more idea.. fixing beer help help me a lot, thanks a lot..

    Posted by Loumar Pablei on September 07, 2023
  • So, that was 1200 mL of starter into 5 gallons?

    Posted by Tony Powell on December 05, 2022

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