Sometimes, after I have quickly cooled my sample, my pH meter stops at a higher than expected pH reading. I can swirl the sample and the pH drops into a more expected reading within reasonable tolerance.
I think I’ve been inducing a false reading after the swirl (or two.. or three).
The theory is that by swirling I am introducing CO2 from the air resulting in developing carbonic acid causing the sample pH to lower to my expectation. When in reality, despite being higher than estimated, my sample pH reading was accurate before swirling
I’ve read this on the internet and was interested in other’s thoughts:
For more accurate pH measurement
For the most accurate and stable pH readings it is recommended to:
Minimize air exposure: Handle samples quickly and avoid excessive agitation.
Use a proper probe: Allow the pH probe to stabilize in the sample without constant stirring. While a gentle swirl can help achieve a stable initial reading, continued swirling can interfere with the measurement.
Measure immediately: Measure the pH as soon as possible after collecting the sample.
I can tell you that when I got a chance to brew at Sierra Nevadap, the sample was swirled and sat for a while before reading. I dunno if that’s the “right" way, but their results speak for themselves.
I normally swirl my pH probe in the sample a few times before letting it settle. It allows me to get a faster stabilized reading as opposed to waiting several minutes for the reading. I can’t speak for the introduction of much CO2 into the sample by swirling it several times. My guess that unless the sample is vigorously agitated, he amount of CO2 being dissolved in the sample would be very small and would effect the reading very little. Furthermore, it would take any CO2 introduced in the sample a while to achieve equilibrium in the sample, probably much longer than the time it would take to get an accurate reading.
You could test your theory by taking two water samples swirling one aggressively and not swirling the other sample. That might give you more definitive proof of your theory.
CO2 dissolves very quickly, forming carbonic acid which brings pH down, leading to false readings. It is extremely important not to swirl the sample at all while taking the reading. Just let it sit until stable.
I quickly chill to my wort sample to my meter’s calibration temperature (65F) in an ice bath and then insert the pH probe for measurement. I swirl only slightly and briefly. I agree that the sample shouldn’t be mixed too much.
I gently swirl and rather quickly get a stable reading. Sometimes pH stabilizes a tick lower, sometimes a tick higher, after swirling vs. when I first submerse the probe.
These observations tell me that any CO2 dissolving is not enough to matter. If it mattered, pH would never stabilize, and would only keep going down with gentle swirling, as CO2 continued to dissolve.
Gentle swirling prevents nano-gradients from forming around the probe glass. Same logic behind stirring the mash or gently moving around a thermometer.
Is there not CO2 from the atmosphere in contact with the wort for the duration of the mash? While cooling it would increase solubility a bit, this is very low on the list of things I worry about. As was already said, not agitating the probe can lead to a localized concentration of ions on the surface of the probe, since the mode of operation is ion diffusion across the membrane. A gentle stir helps the reading stabilize faster.
I keep two small ramekins in the freezer. Then, after about 15 minutes, I use a small strainer and dip it into the mash so the liquid fills the bottom of the strainer and not the grain. Then I use a turkey baster to suck a small amount of liquid from the strainer and deposit it into the frozen ramekin. Then I use my thermometer to mix the liquid while the temperature rapidly drops to room temperature before testing the pH. And, to put a good word in for Mr. Martin Brungard, my pH has been spot on the predicted about 98% of the time using Bru’n Water Calculator.