PH meter & ATC question

Australia & New Zealand Homebrewing Forum

Help Support Australia & New Zealand Homebrewing Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
Reaction score
i have managed to get me mitts on a PH meter that has an ATC function built in. I have calibration fluid (4,7 & 10) and have plugged in my Melbourne water profile, grain bill and salt additions into EZ water calc.

I brewed 2 saisons over the past week. same grain bill, water volumes, mash temps etc. I did change salt additions which is why P/H estimates below vary between the brews.

First brew:

EZ water calc estimated room temp PH 5.53

i took a sample after 15 mins and let it cool a little and got a reading of 5.2. ATC read 30.8 degrees

a difference of .33 P/H

Second brew:

EZ water calc estimated room temp PH 5.66

i took a sample after 15 mins and let it cool a little and got a reading of 5.59. ATC read 26.2 degrees

a difference of .07 P/H

I have read from many on here how they get very close or spot on to what EZ calc estimates re P/H and am wondering why my readings are out.

so can I take a reading in any temp sample (not over 50 degrees) and it automatically adjusts it for 25 degrees? So what reading the meter gives is room temp adjusted? There is no instructions with the meter.

any direction or advice would be greatly appreciated.....cheers
One problem is that the actual pH of the mash changes due to temperature - this is a property that brewing mash has, but not every liquid you would test with a pH meter has. This is completely separate to the change due to temperature that the ATC of your probe compensates for. As usual ajdelange sums this problem up pretty well.

The EZ water pH prediction is likely based on my work. For comparison you can also enter your data here:
This is a calculator I wrote for Brewer's Friend and which we released just recently.

For the most part pH prediction can be pretty accurate but there are going to be outliers and I would trust your pH meter over any such calculator. Especially if the pH prediction is based on the color and type of the grains compared to using actual pH characteristics of the grains.

But I still like to understand where the outliers are coming from. Would you be able to give me some more detail on the water, additions and grist composition that you used for these two beers?


Good to see you joined our forums, Kai, very much looking forward to your contributions.

Welcome, mate!

There are a few things going on with your meter that influence the pH reading and how it relates to the actual pH of your samples. The thing about a pH meter, even an ATC one, is that it doesn't directly measure pH (the concentration of H+ ions)--it measures the electrochemical potential across the probe tip and relates that to pH. The way it establishes the relationship between the potential and pH is by recording the potentials of your pH 4, 7, and 10 standard solutions.

The relationship between potential and pH changes with temperature for both the standards and your samples. So it's important to know the actual pH of your standards when you are calibrating the meter. The standards bottles should say something like "pH 7.001 at 25 C" or have a table of the different pH at different temps. Chances are the standards are really close to 4, 7, and 10 at 20 C or 25 C, so if you just calibrate the meter at around 20-25 C, then it should be fairly accurate.

Once you've got the meter calibrated with the correct pH of the standards at the calibration temp, then the meter knows the relationship between potential and pH. That relationship changes with sample temp, but in a predictable way, and the ATC compensates for that. So, if you measure a sample at 40 C and the meter says it's pH 5.3, then that pH really does accurately reflect the H+ ion concentration at 40 C.

The catch with all this is that your samples are complex and have inherent buffering characteristics that change with temperature--that is what Dent mentioned--the actual sample pH changes with temperature. For example, a wort sample might read pH 5.2 at 60 C and 5.6 at 25 C and both would be correct--the meter isn't wrong, the samples really are different pH at different temps.

Choosing what pH readings you use and the temps just depends on what you want to get out of your measurements. If you calibrate your pH meter with fresh standards on the same day you use it and it doesn't produce any errors, then it's probably accurate, but only at the temp of the sample at the time of measurement.
Florian said:

Good to see you joined our forums, Kai, very much looking forward to your contributions.

Welcome, mate!
Thanks. I feel if I stay too much in one place I get only exposed to a more limited set about brewing practices.


your points about ATC and temperature dependent pH shift are correct, but symphony did take the pH measurements close enough to standard temperature that I don't think this is going on here.

thanks so much for the informed replies gents! in am effort to try and understand what my measurements mean, I am brewing again next week and will ensure my calibration solution and then my mash samples are measured at a constant room temperature. that way I can eliminate the temperature variability. Once I have done that I will report back and ask more questions I am sure!.....

Thanks again for the help! :)

Latest posts