Have I been measuring mash pH wrong?

I've been focusing on my water chemistry the last 6 or 7 batches and thought I had it all dialed in. I started with both EZ Water and Bru'n Water and found Bru'n Water to be a bit more accurate for my system so I have been using that the last several batches. I use a Thermoworks 8100 with ATC which I calibrate every time before use and measure approximately 20-30 min into the mash, and adjust with calcium chloride, gypsum, epsom salt, and 88% lactic acid.

http://www.thermoworks.com/products/ph/8100ph_meter.html

Now, I have always measured my mash pH directly in the mash itself, with both the temp probe and electrode into the mash. I have been hitting 5.2-5.3 on my pale/IPA type beers and trying to get closer to 5.4-5.5 for porters/stouts at MASH temperature, not room temp. Now, I think I may have confused myself a bit when reading this thread -

https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

Have I been doing this right and targeting the right values? Should I be measuring these at room temp and targeting 5.2-5.6? I seem to hit just about dead on with Bru'n Water with +/- 0.05 pH from what it says I should (when measuring at mash temp). I have been running into some low mash efficiency problems with my new setup and was thinking this may be the problem. The last few batches have been 5.2-5.3pH @ 154-155F.

Theoretically, the ATC feature corrects for temp so your readings should be equivalent to "room temperature"
That being said, I find that I get much longer life from my probes if I do not subject them to high temperatures. Cooling the sample first is a good idea.

ATC does not correct for the temperature-dependent pH change due to mash chemistry. It only corrects for the probe's change in response with temperature. You must still reduce the wort temperature to near room-temperature to avoid those problems.

You can read more about important reasons to perform your pH checks at room-temperature on the Bru'n Water Facebook page.

Go back and reread https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ a bit more carefully. It tells you exactly what ATC does and what it does not do (correct for the actual change in mash pH with temperature).

This is a thorny problem. The reactions of interest obviously take place at mash temperature and so it is only common sense that we would want to take mash pH readings at mash pH temperature. This would stress electrodes shortening their lives so we would prefer not to do that. Another problem is that there are many 'mash temperatures': dough in, beta glucan rest, protein rest, low saccharification rest, high saccharification rest. It would complicate discussions in places like HBT, the literature and textbooks if we had to say mash pH should be between x and y at dough in, between u and v at low saccharifiation rest temperature and... Add to this that when people started taking pH measurements it usually involved transporting the sample out of the brewery to the lab and so the sample had cooled anyway. It became standard practice to quote mash pH at laboratory temperature and that is what is generally, but not always, done today. Gordon Strong, for example, quotes mash pH at mash temperature.

Using room temperature has it's limitations. I've always used 0.0055 pH/°C as the glide because all the mashes where I have checked it showed a glide close to that. But in measuring malts for pH prediction I am finding that some malts exhibit glides appreciably more than that. Thus mash pH predictions and measurements at room temperature are a little squishy. It's sort of like airplanes. At high altitudes the altimeter settings from local airports aren't applicable and so everyone sets his altimeter to 29.92. The altimeter doesn't read the real altitude but if two guys have the same altimeter reading they are at the same altitude and better watch out for each other. If you mash pH reads 5.52 at room temperature the pH at mash temperature probably isn't 5.52 - 0.0055*∆T but if room temp. pH of 5.52 produces good beer then you can control for that and succeed.

Thanks everyone.

So it is safe to say that my mash temp pH readings of my last two beers of 5.22 and 5.25 @ 152-155F is actually closer to 4.9-5.0pH at room temp?

I have not been as happy with the last few beers and mash efficiency has struggled, so I believe this may well be my culprit. I understand the personal preference aspect of it, but I need to start where the most accepted range is, and then fine tune from there.

On my previous setup I was actually hitting closer to 5.45-5.55 pH at 150-155F and was much happier with the beers. So it seems there is some correlation.

Taking pH readings at room temp should not only help with my beer in flavor and mash efficiency, but also life of the probe as well.

No, other way around (yes, I did have the sign wrong in #4 -sorry). Higher temperature implies higher pH so that your 5.25 at mash temp might be about 5.5 at room temp.

Hmm, guess I'll keep searching.

I will be measuring a cooled sample from now on.

Lots of us pull a sample in a little beaker or shot glass. I use a 50 ml beaker, and I only need 10 or 15 ml of liquid to get a sample. If you run cool water over the outside of the shot glass/beaker, it gets to room temp in no time.

Was browsing back through Brewing Better Beer by Gordon Strong and he does mention measuring pH at mash temperature, and not room temperature, and gives the approximate correction factor. I think that's where I must have had the information from in my head to measure at mash temp and not room temp. To be fair, my meter probably sees a total of 90 seconds at 150+*F in a given year, so not extended periods. And also mentions that it is capable between temps of 212*F.

It's like a light bulb (in the days before the government told us what kind of light bulbs we are allowed to buy). It's not so much the time at elevated temperature that is the problem as it is the transition from cold to hot and then hot to cold.

There are plenty of pH probes that are rated for high temperature use, but as AJ said, its the thermal shock of going from room-temp to mash-temp and back that destroys the instrument.

So unless you are going to store your probe at around 150F, you are better off reducing the temp of your wort sample to room-temp.