Ask The Brewmasters

Typically, I knockout with a target pH of 4.80 for dry hopped beers, which puts me in the 4.35 range post fermentation.  This time around, between two turns, I yielded an average of 4.90 which left my post fermentation pH slightly higher than normal.  Does anyone have any information, or perhaps a calculator, for how much lactic acid to add to a fermenter to adjust the pH for dry hopping?  I've searched through the community discussions and can't find anything.  Also, would you adjust the pH prior to dry hopping or after?

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Thanks,

Ben
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Hi Ben!

There is no general formula because the the buffering capacity of the beer depends on its composition. The straightforward approach is to make up a solution of lactic acid in water and add it in increments. It may be easier to pull a representative same and do the measurement on a smaller scale. So if you have 10 hL in the fermenter, pull, say, 5 L and add increments of your LA solution to that until the desired pH is reached, then add that amount, scaled up to the FV. The scaling factor in this example would be 1000 L / 5 L = 200, so if it took 50 mL for the 5 L sample, use 50 mL x 200 = 10000 mL = 10 L in the FV.

That said, the difference between pH 4.8 and 4.9 is barely within the discrimination of a pH measurement (typically 0.05). A difference of a few degrees for the calibration or measurement temperature could account for it. Measured pH decreases as temperature goes up. 

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Roger Barth
Emeritus Professor of Chemistry
West Chester University
Author (with Matthew Farber) of
Mastering Brewing Science, 2nd Edition
ISBN 978-1-119-78333-0
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Hi Folks,

I agree with previous comments. Remember that Lactic Acid is a weak acid. A large dose may not have much impact on pH due to a robust buffering capacity. Every wort is different, so a "Rule of Thumb" is not possible. When working with weak organic acids, adjusting pH has to be done empirically on a brand-by-brand basis. In some cases, you could add a significant acid dose with minimal pH bump but the undissociated acid will leave a noticeable sour twang even though the pH impact is moderate. pH is certainly important but also consider "% acidity" as winemakers do.

Regards,

Daniel Carey

New Glarus Brewing Company

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Daniel Carey
Brewmaster
New Glarus Brewing Company
New Glarus WI
(608) 527-5850
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Original Message:
Sent: 04-09-2025 16:49
From: Roger Barth
Subject: Lactic Acid in the Fermenter to Adjust pH for Dry Hopping

Hi Ben!

There is no general formula because the the buffering capacity of the beer depends on its composition. The straightforward approach is to make up a solution of lactic acid in water and add it in increments. It may be easier to pull a representative same and do the measurement on a smaller scale. So if you have 10 hL in the fermenter, pull, say, 5 L and add increments of your LA solution to that until the desired pH is reached, then add that amount, scaled up to the FV. The scaling factor in this example would be 1000 L / 5 L = 200, so if it took 50 mL for the 5 L sample, use 50 mL x 200 = 10000 mL = 10 L in the FV.

That said, the difference between pH 4.8 and 4.9 is barely within the discrimination of a pH measurement (typically 0.05). A difference of a few degrees for the calibration or measurement temperature could account for it. Measured pH decreases as temperature goes up. 

------------------------------
Roger Barth
Emeritus Professor of Chemistry
West Chester University
Author (with Matthew Farber) of
Mastering Brewing Science, 2nd Edition
ISBN 978-1-119-78333-0
------------------------------

Hey Ben,

Roger is spot on. There's no calculator because pH depends on so many factors that it's functionally unique to each brewery. Pulling a small amount off and testing is the way to go here. I will also add on that dry hopping actually causes an increase in pH. Again the increase will depend on your specific beer, but Karl Ockert's Craft Brewers Guide to Best Practices has an estimation where the expected pH increase is 0.14 pH units per 0.4 kg/hl (1 lb./bbl) of added dry hops. So depending on when you usually measure pH make sure to test your acid addition to reach your target at that point.

Cheers!

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Nate Denzin
Gnarly Cedar Brewery
Greenleaf WI
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Hi Ben
We have a better opportunity to ask ourselves this question: "What has changed in the process?

If we admit that the pH meter is calibrated and that the pH of the wort is normal, then I propose to investigate these points:

1.Temperature and Contact Time.
Warmer dry hopping time and long contact times increase extraction of compounds that impact pH.
2. High dry hop loads 
 has higher impact on pH value.

For 10 bbl (310 gallons):
310 mL of 88% lactic acid should lower pH ~0.1

Moreover, it's a best practice to add lactic acid before dry hopping.

Kind regards

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Paul Kapopo
Brewing & Quality Trainer
BRALIMA / HEINEKEN
KINSHASA
+243998943281
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Hi Ben,

As a sanity check on a titration (small pipette measurements can lead to big errors), you could cap your total acid addition at roughly the amount you'd normally add to the kettle/whirlpool to achieve your target knockout pH. At first, I'd also wait to add the acid until after fermentation and yeast removal. I don't know if "pH shock" is an issue for yeast - but if I was you, I'd assume it is until evidence suggests otherwise.

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Joe Walts
Quality Manager and R&D Brewer
Karben4 Brewing
Madison WI
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Ben,

The few times we have adjusted beer pH post-fermentation, we've used phosphoric acid. Benchtop-titration per batch to determine dosage rate, but the ultimate benefit of phosphoric is very little aroma / flavor effect. Conversely, too much lactic is easily noticeable. And gross. If you don't believe me, benchtop phosphoric vs. lactic, and be prepared to spit out the lactic.

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Daniel Stavig
Head Brewer
Indeed Brewing Company
Minneapolis MN
(763) 218-8781
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