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The Case for Underpitching Yeast: Foolish or Genius?

The Case for Underpitching Yeast: Foolish or Genius?

The advice across the board is generally simple; don't underpitch yeast. If anything, the advice is to overpitch your yeast just in case, so you have more than enough to complete fermentation. Therefore, when would you ever underpitch intentionally?

Brandon Copeland
February 09, 2025

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-Brandon Copeland

The Case for Underpitching Yeast: Foolish or Genius?

Yeast pitching rates have long been a sacred rule in brewing: "Always pitch the right amount of healthy yeast." We've all seen the calculators and the formulas, and for good reason—underpitching can lead to sluggish fermentation, off-flavors, and a stalled brew.

But here’s the thing… some brewers are intentionally underpitching yeast. And not just for the thrill of breaking brewing dogma.

What Happens When You Underpitch?

If you’ve ever accidentally underpitched yeast (say, by reusing an old smack pack that barely inflated), you might have noticed some weird things happening:

Longer lag phase – Fermentation takes its sweet time kicking off.
More ester production – Fruity, funky, sometimes unpredictable flavors emerge.
Higher residual sweetness – Some strains don’t fully attenuate when underpitched.

For most styles, this is a problem—you get off-flavors, sluggish fermentation, or even a stuck ferment. But for certain beer styles, underpitching is used deliberately to enhance ester and phenol production.

When (and Why) Would You Underpitch?

Belgian ales? Some breweries swear by underpitching to boost esters and phenols in their Trappist-style beers. Think of those classic banana and clove notes in a good tripel or hefeweizen—sometimes, a little yeast stress enhances those signature flavors.

New England IPAs? Some brewers suggest underpitching can help yeast stay in suspension longer, promoting the hazy look and juicy mouthfeel.

Kveik strains? This Nordic yeast ferments hot and fast, and some claim that underpitching can coax out even more tropical flavors.

The Risk Factor

Of course, it’s not all magic and flavor enhancement. Underpitching can:

Cause acetaldehyde (green apple) and diacetyl (buttery) issues
Increase risk of infection due to slow yeast dominance
Lead to stalled fermentation if the yeast can’t handle the stress

So is it worth experimenting? Or is it just brewing with unnecessary risk?

Your Turn: Would You Try Underpitching Yeast?

Have you ever intentionally underpitched yeast for flavor impact? Or is this just another homebrew myth waiting to ruin a batch?

Beer Trivia Question

🍺 Which historical brewing tradition often relied on underpitching yeast due to the lack of commercially available yeast strains, leading to unique fermentation characteristics?

Read to the end to find out if you're right!

Brewgr Recipe of the Week

Session IPA 50L

Recently I have been gravitating toward Session IPAs that are low in alcohol content, flavorful enough without being overbearing or too bitter, and very crushable so you can have a few. This beer checks those boxes, with mostly pilsner malt and Citra dry hopped.

Credit: RIGUETESBEER

Poll Results: How Do You Approach Water Chemistry in Brewing?

Most of our poll respondents prefer to make minor water chemistry adjustments, but they aren’t losing sleep over the details. However, in a close second, many brewers are very meticulous about their water chemistry adjustments.

Admittedly, sometimes I am lazy and fall somewhere in between just using tap water and making minor adjustments based on the style - I’m blessed with good NYC water and don’t stress too much about it. Definitely something I want to improve on in the future though…

And the Answer Is...

🍺 Lambic brewing in Belgium. Traditional Lambics rely on spontaneous fermentation, meaning brewers do not pitch yeast at all. Instead, wild yeast and bacteria from the environment (such as Brettanomyces and Pediococcus) inoculate the wort as it cools in open-air vessels called coolships. This underpitching—or lack of pitching altogether—contributes to Lambic’s signature tart, funky, and complex profile.

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Happy Brewing!

- Brandon, Brew Great Beer Team

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The Case for Underpitching Yeast: Foolish or Genius?

The advice across the board is generally simple; don't underpitch yeast. If anything, the advice is to overpitch your yeast just in case, so you have more than enough to complete fermentation. Therefore, when would you ever underpitch intentionally?