New to mash chemistry, why is my pH so much lower than predicted?

I've been doing a lot of reading and think I have a good handle on mash chemistry basics in theory. I recently bought the milwaukee MW102 pH meter (with the thermometer attached) and calibrated it with pre-mixed pH 4 and 7 buffer solutions I bought on amazon following the calibration tips in the sticky here.

So I made two beers last weekend and took my first readings about 15 minutes after dough in, and cooled the wort to ~70F before measuring. In both cases the pH measured was ~0.3 lower than that predicted by brun' water. perhaps I haven't filled out brun water correctly? or do you think my meter may not be correctly calibrated? I'm just looking for some advice. Below is a screenshot of the relevant tabs from brun' water for the brown ale I made, as well as a water report from my city taken last week. For this mash I measured a pH of 5.0.

FWIW I added a bit of chocolate malt for color 15 minutes before the end of the mash, so I didn't include those in the Brun' water data. pH was measured before that addition as well.

I welcome any help/input/advice. Thanks

Check some of the other recent posts here and you will see quite a bit of discussion as to why calculators can be pretty far off. The main reason is that they don't really know the properties of the malts you are using. Color is a poor proxy for DI mash pH and buffering (the two most important parameters). If a program allows specification of actual DI mash pH, enter the best value you have for that. If the program does not allow specification of DI mash pH you can still force a program to think DI mash pH is lower than the program assumes by telling it that the color is higher and conversely.

An error of ±0.3 is pretty big, however. Big enough to warrant a careful check of all your entries.

I've done two estimations of mash pH for you grain bill, both of which give a pH significantly above 5.0. One estimation (5.49) uses an empirical calculator (similar to BW) while my other estimation (5.47) is directly based on distilled water pH and buffering capacity values for your grains (some values known from measurements and some inferred from data from similar malts). It is hard to see how your grain bill would produce a pH of 5.0 with your water, which has an RA very close to zero. Only ~20% of your grains have DI pH's less than 5.0, and only that of Special B is greater than 0.1 below 5.0. Cheers!

dmr said:

I've done two estimations of mash pH for you grain bill, both of which give a pH significantly above 5.0. One estimation (5.49) uses an empirical calculator (similar to BW) while my other estimation (5.47) is directly based on distilled water pH and buffering capacity values for your grains (some values known from measurements and some inferred from data from similar malts). It is hard to see how your grain bill would produce a pH of 5.0 with your water, which has an RA very close to zero. Only ~20% of your grains have DI pH's less than 5.0, and only that of Special B is greater than 0.1 below 5.0. Cheers!

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Thanks for looking at this for me.

So is that suggesting my meter calibration is off? not sure what else could be going on. I can order some solutions from a different vendor and see if my measurement matches the brunwater calculator better this weekend.

Run a stability check on your meter using the instructions at https://www.homebrewtalk.com/showthread.php?t=302256

dmr said:

I've done two estimations of mash pH for you grain bill, both of which give a pH significantly above 5.0. One estimation (5.49) uses an empirical calculator (similar to BW) while my other estimation (5.47) is directly based on distilled water pH and buffering capacity values for your grains (some values known from measurements and some inferred from data from similar malts). It is hard to see how your grain bill would produce a pH of 5.0 with your water, which has an RA very close to zero. Only ~20% of your grains have DI pH's less than 5.0, and only that of Special B is greater than 0.1 below 5.0. Cheers!

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Thanks so much for the time you spent looking into this for me. Based on your post I figured out that the calibration solutions I bought to calibrate my probe for the first time sucked!

I purchased some Milwaukee calibration sachets and redid the calibration last night. My first two readings of mash pH were coming in about 0.3-0.4 lower than what Brunwater predicted. So last night I measured my starsan bath and the beer I was drinking then redid calibration with milwaukee solutions, now both those things came in about 0.4 higher. Now I stuck my probe in the other calibration solutions I bought, 4.32 for the pH 4, 7.22 for the pH 7. What garbage!

I ran a stability check on my probe and meter with 5 measurements from 8-10:30pm last night and it was 4.00 every time. I'm excited to get my first true pH reading for the brew this weekend.

Thanks for the help figuring this out everyone, and please dont buy these calibration solutions from atlas scientific!

HausBrauerei_Harvey said:

Thanks for the help figuring this out everyone, and please dont buy these calibration solutions from atlas scientific!

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I gave some poor guy in another thread a whole litany on pH measurement practices because I refused to believe that anyone would sell buffers that were off by as much as these apparently are. But it seems to be true that these buffers are indeed that far off. So heed this warning!

Glad you found the issue, at least it is very easy to correct

So I did my first brew this weekend with my correctly calibrated meter. Brunwater predicted a RT mash pH of 5.46, I measured a RT mash pH of 5.45. Man that was a good feeling! I've been reading off and on about mash chemistry adjustment for over a year, so its nice to feel like I'm on my way to a deep dive into water adjustment.

Thanks again everyone, I am now greatly looking forward to tweaking my recipes via mash chemistry.