Why Do I Have Acetaldehyde in My Beer?

The heading of this article “why do I have acetaldehyde in my beer”, is self-explanatory. The off-flavor acetaldehyde, which presents as “green apples” in beer, was a suggested by a reader.

I’m writing this article in response to the email below from a brewer called Sean.

Why Do I Have Acetaldehyde in My Beer - Original Email

He was having issues with acetaldehyde in his brews. I said, I’d write an article first, share it with him and then we’d have a chat after. So, here we are…

What is Acetaldehyde?

Acetaldehyde smells and tastes like fresh green apples in beer. Have you ever had “Granny Smiths” apples? Brewers suggest the flavor of this variety, is a lot like acetaldehyde.

In some beers at lower levels, it’s encouraged. In Biere de Garde and American lagers for instance, it’s part of the flavor profile. Acetaldehyde is present in all beers, to some extent.

Budweiser, actually contains low levels of acetaldehyde, as part of its flavor profile. The idea being the acetaldehyde adds a “fresh crispness’ to the beer. It’s all about the “sensory threshold” for acetaldehyde.

The Sensory Threshold – Why Do I Have Acetaldehyde in My Beer?

The common belief is the threshold for acetaldehyde is between 5-15mg per liter. In pale/lighter beers, the flavor threshold is at the lower end of the scale.

If a drinker orders a glass of beer and it smells like green apples. The chances are the brewery rushed the beer to market, and it’s a little too “green”.

Please note: If the beer smells like paint or bruised apples. Then there are bigger issues at play. It’s a sign of problems somewhere along the brewing process.

In this instance as a drinker, you’d be within your rights to take the beer back. Although, even at higher levels acetaldehyde, isn’t unpalatable.

However, it’s still an off-flavor, and an indication of problems in the brewing process.

Furthermore, it’s worth nothing you do have beers like Unibroue Éphémère. Which is a fruit beer designed to have pronounced apple notes. Always make sure you know what beer you’re ordering/drinking.

Why Do I Have Acetaldehyde in My Beer? Overview

Why Do I Have Acetaldehyde in My Beer? As an Off-Flavor

When the concentration of acetaldehyde is above, or well above sensory threshold, it becomes an off-flavor.

It’s formed at the beginning to middle of beer fermentation. And is tied to yeast health. It’s produced by yeast as a precursor to ethanol.

In a typical fermentation its concentration will decrease, as the beer reaches terminal gravity as well as through the maturation process.

Acetaldehyde can also be caused by oxidation, where too much O2 is present in the packaged beer.

Oxidization may lead to residual sugars turning into acetaldehyde. Whilst at the same time oxidizing ethanol to ethanoic (acetic) acid.

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Why Do I Have Acetaldehyde in My Beer? How To Control Acetaldehyde Production in A Brewery?

There are practices a brewery can implement, to guard against acetaldehyde, which are:

  • Make sure to pitch the correct amount of yeast – Use suggested fermentation temperatures from your yeast suppliers too.
  • Provide adequate wort FAN (100 to 140 mg/L in normal wort gravity)
  • The wort needs adequate wort zinc (0.48 to 1.07 mg/L)
  • Aerate wort with clean air or pure oxygen (8 to 10 mg/L)
  • Once the fermentation has kicked off; avoid any additional wort aeration.
  • In most lager fermentations, allowing the fermentation to finish at a slightly higher temperature is recommended. Check with you yeast supplier, as some yeasts like W-34/70 ferment clean, at quite high fermentation temps.
  • Use a diacetyl rest
  • Always use proper sanitation practices throughout the whole brewing process.
  • It’s advised to wait a few days after the fermentation is finished, before racking off the yeast.

Furthermore, there are a few actions to avoid as well, which are:

  • Avoid removal or dropping of yeast too early
  • Extended periods of warm maturation, can cause acetaldehyde levels to rise as yeast loses viability.
  • Ensure there isn’t any non-viable yeast in the beer, if it’s maturing for extended periods of time.
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Sometimes Beer Just Needs More Time in The Cellar

Healthy Yeast Is Key

In general, acetaldehyde is avoidable as long as the fermentation and maturation process are properly handled. Acetaldehyde is most often formed, when beer has been sitting on yeast too long.

When yeast health is poor, cells may die, bursting open (autolysis) leading to release of acetaldehyde into beer. A brewer should ensure there’s a strict yeast dumping regime during maturation.

Furthermore, keeping young beer in contact with a healthy population of yeast causes re-absorption of acetaldehyde. Going a long way in reducing levels of this compound.

As with many processes in brewing, it’s best to be patient. Give the brew a few days after reaching terminal gravity, before racking the beer to secondary.

Video on the 20 most common beer off-flavors – Press pause if you need to review any infromation further

Why Do I Have Acetaldehyde in My Beer? Proactive Solutions

Kräusening, is the best option, similar to diacetyl if you’ve excess acetaldehyde. Kräusening is the process of adding a proportion of active wort to a brew nearly fully fermented.

The term “kräusen” refers to wort at its most active state of fermentation. It’s when the blow-off-bucket, overflows with foam, for example.

Its why brewers should never dump yeast/rack off too early. As we’ve said before, raising the temperature of the fermentation before it’s finished, helps too.

Furthermore, proper cellar care is crucial too. As mentioned before, oxygen pickup can be a problem. So, cellar processes have to be tight. For example, proper dry-hopping SOP’s need to be in place.

What Are Hops - Hop Pellets
Brewers Need a Good Dry-Hopping Process To Avoid O2 Pick-Up

Conclusions – Why Do I Have Acetaldehyde in My Beer?

Acetaldehyde, is one of the easier off flavors to pick-up. With sensory from green apples, squash like, jolly ranchers even to latex paint. In general, a brewery with good SOP’s shouldn’t experience this compound, in their finished beers.

However, an issue with fermentation cooling, bad yeast pitch or an unforeseen issue with the wort, may lead to acetaldehyde issues.

In this instance, give the beer some time to see if the acetaldehyde is re-absorbed. If this doesn’t fix the issue, then kräusening is final option to try.

Well, I hope this post has helped a few people. When it comes to acetaldehyde and brewing. If you’ve any feedback, follow-up questions or would like to chat further, then feel free to email me at:


You can also reach me through your preferred social network too. Scan the relevant QR code below, add me and message me there directly.

Likewise, if you’d like to discuss a brewing project, please get in touch. We can arrange time for a chat. For now, thanks for reading, happy brewing and have a great day.

Neil Playfoot

Neil is a brewer with 25 years international brewing experience. Based out of China (first came in 2010) he works as a brewing consultant helping brewers with their projects and brewing processes. To find out what services Neil can provide your brewery please click here. If you'd like to contact Neil you can email at neil@asianbeernetwork.com.
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