Measuring Ph of mash and temp corrected readings

[TheHopfather]

Interesting topic OP, I was wondering the same thing myself. I've searched and searched for info about mash and room temp pH samples and could never find a straight answer.

@mabrungard - this might be an extremely simple question but does BrunWater calculate the target pH at mash temp or at room temp? I would assume mash temp, which means my room temp samples should be 0.2 ~ 0.3 pH higher then what is actually happening in the mash?

I think my confusion lies in looking at blog posts and such that are showing pH samples reading 5.2. You would think those samples would be cooled, and should be showing higher than that. I'm never quite sure if I should be adjusting my room temp samples down a bit or not.

 

[user 246304]

That's what the stability test is intended to do. See
https://www.homebrewtalk.com/showthread.php?t=302256

Thanks AJ. Some reading to do, I see.

 

[Big Monk]

PS: Does anyone else have a problem with participants authoritatively posting on this forum while remaining comfortably anonymous behind an assumed avatar? You'll notice that AJ and I stand behind our names for what we say on this forum. It certainly keeps us honest.

I think the varying levels of anonymity here are the most frustrating aspect. Some people, like yourself and AJ are 100% transparent. Others, like myself for instance, are known but not open in the online presence sense.

There are however people posting on all forums, not just here, who use anonymity to present half formed ideas and opinions.

My wife will tell you i'm not an authority on anything besides annoying the crap out of her.

 

[rhys333]

Okay, so my new Thermoworks 8689 comes with ATC. When I test the 7.0 buffer solution my meter recognizes the solution and the display says 6.88 ever time. The manual that comes with my pH meter says its supposed to do this if everything is working well, so this is good.

However, the table on the buffer solution says that at 22 degree C, the readout should be 7.01 instead of 6.88. I've heard that I should use these numbers, so I recalibrate my readout from 6.88 to 7.01. Should I be doing this, or should I trust that ATC has sorted everything out for me and leave the readout at 6.88?

 

[mabrungard]

My wife will tell you i'm not an authority on anything besides annoying the crap out of her.

Then your wife and mine must be sisters!

Regarding the temperature used in Bru'n Water for pH estimation: The instructions in Bru'n Water do emphatically state that all pH prediction is based on room-temperature measurement.

 

[ajdelange]

Okay, so my new Thermoworks 8689 comes with ATC. When I test the 7.0 buffer solution my meter recognizes the solution and the display says 6.88 ever time.

You have purchased a meter that is intended to be calibrated with NIST standard buffers. These are rarely used except in the laboratory. Most meters use NIST traceable 'operational' buffers. With them if the meter sees, during cal, a buffer near 7 it assumes it is a NIST traceable operational buffer and proceeds to do the calibration based on pH values for that meter stored in its memory. If you present such a buffer to your meter it will assume that it is a NIST buffer and proceed to calibrate presumably based on the tables for that buffer unless you tell it that the pH is something different which apparently you must do. Now what I can't tell from the manual is how this entry is treated with respect to temperature variation. Are you supposed to enter the pH of the buffer printed on the bottle label or the pH at the calibration table as obtained from the table often furnished with the buffer?

I would be a little skeptical about readings obtained with this meter (though the error is probably appreciably less than 0.1 pH) and would caution others to avoid it because of this.

Should I be doing this, or should I trust that ATC has sorted everything out for me and leave the readout at 6.88?

It's not the ideal situation by any means but yes, you should do this. Better would be to buy NIST buffers (https://www.inorganicventures.com/productdisplay/ph-686-standard-0) and calibrate the meter as it is intended to be calibrated.

 

[Silver_Is_Money]

The easiest way to clarify this for the OP is to state that a pH of 5.1 measured at roughly 150 degrees F. is the same as a pH of 5.4 measured at roughly 70 degrees F. Both readings are nominally correct with reference/respect to the temperature at which they are taken. But always keep in mind that mash pH software presumes that the reading is to be taken at a nominal 70 degrees F., so if you are measuring pH at mash temperature add ~0.3 to nominally bring your meter readings temperature frame of reference in line with the temperature frame of reference of the software.

https://mashmadeeasy.yolasite.com/

 

[Silver_Is_Money]

Water which is neutral reads as follows: https://chem.libretexts.org/Core/Ph...emperature_Dependence_of_the_pH_of_pure_Water

At 10 degrees C. neutral waters meter measured pH = 7.27
At 25 degrees C. neutral waters meter measured pH = 7.00
At 50 degrees C. neutral waters meter measured pH = 6.63

https://mashmadeeasy.yolasite.com/

 

[ajdelange]

The easiest way to clarify this for the OP is to state that a pH of 5.1 measured at roughly 150 degrees F. is the same as a pH of 5.4 measured at roughly 70 degrees F.

I fear that this may actually confuse him more as they aren't the same at all. The pH actually shifts because the pH depends on the number of protons in solution and the hotter something is the more likely (in most cases0 protons will be jiggled free from acid molecules. IOW the pK's drop as temperature increases.

Both readings are nominally correct with reference/respect to the temperature at which they are taken.

pH is pH. If a meter is properly calibrated (including isoelectric pH) it will read the correct pH at any temperature. But one cannot predict the pH at one temperature from the pH at any other temperature unless he knows the details of the composition of the solution and the behaviour of the individual pKs with temperature. This is, of course, impossible with a mash and so the best we can do is make some assumption about how mash pH actually changes with temperature and this we have to do by making meaurements on mashes or on the grains that go into them. If we measure mash at 150 and find its pH to be 5.1 and then cool it to 70 and find it to be 5.4 we have, for that mash, a glide of 0.3/(80/1.8) = 0.00675 pH/°C. That's not an unusual glide. I use 0.0055 when I don't have actual malt information but I have measured malt glides as large as 0.014 pH/°C but more typically around 0.008 to 0.010 pH/°C.

Thus we cannot say that pH 5.4 measured at 70 is the same as pH 5.1 measured at 150 but we can say that pH 5.4 measured at 70 implies that the pH at 150 is somewhere in the region 4.96 to 5.16.

But always keep in mind that mash pH software presumes that the reading is to be taken at a nominal 70 degrees F., so if you are measuring pH at mash temperature add ~0.3 to nominally bring your meter readings temperature frame of reference in line with the temperature frame of reference of the software.

I would suggest that anyone taking pH readings at mash temperature set the sample aside and record pH at a couple of other temperatures down to room temperature. By so doing he can determine what the glide for his mash actually is and then use that to determine pH at mash temperature from future (for that grist composition) readings at room temperature.

 

[ajdelange]

Water which is neutral reads as follows: https://chem.libretexts.org/Core/Ph...emperature_Dependence_of_the_pH_of_pure_Water

At 10 degrees C. neutral waters meter measured pH = 7.27
At 25 degrees C. neutral waters meter measured pH = 7.00
At 50 degrees C. neutral waters meter measured pH = 6.63

These are half the pK's of pure water at the given temperatures. While pure water would measure those values were it possible to measure it they really represent the neutral pH i.e. the pH at which the concentrations of H+ and (OH)- are equal (and equal to 10^-pK/2). The pKs can be conveniently computed in an Excel spreadsheet from

=4471/A1 +0.01706*A1-6.0875

in which A1 contains the temperature in K (= 273.15 + °C). The pH of pure water at a given temperature is pK/2. So this illustrates the statement I made in the last post that when temperature goes up, pK goes down and H+ ion concentration goes up.

Readers should not expect to be able to obtain any of the numbers from the formula or listed values if attempting to measure the pH of pure (or DI or RO) water as measurement as it is difficult. It is a pretty good insulator and pH measurement relies on current flow. Also it is quickly contaminated by CO2 from the atmosphere which lowers its pH. Air must absolutely be excluded, special buffers are required to calibrate the meter and ion strength adjusters must be added to the sample.

 

[ajdelange]

AJ, don't know whether you'd be willing to opine (I'd understand if not), but would you put the Extech into the class of cheap, undependable meters?

I don't know anything about it and thus cannot say one way or the other.

Do you have a recommendation for a portable one, a good one for brewday when one can't conveniently walk to the lab bench?

A lot of people here like the Hach pH Plus. There is a similar Omega product which some people here have reported favorably on. Hanna has a relatively new offering especially for brewers (titanium body) that works through your smart phone which at first look seems good. The other meter that a lot of people here use is the Milwaukee MW102 but that is a benchtop meter (of comparable price).

 

[user 246304]

I don't know anything about it and thus cannot say one way or the other.
A lot of people here like the Hach pH Plus. There is a similar Omega product which some people here have reported favorably on. Hanna has a relatively new offering especially for brewers (titanium body) that works through your smart phone which at first look seems good. The other meter that a lot of people here use is the Milwaukee MW102 but that is a benchtop meter (of comparable price).

Thanks AJ. I haven't had a chance to read your lengthy work of yesterday or the day before, hit with some bad news which has slowed me some, but I do intend to go through it. Just a query on the milwaukees - these appear portable to me. Are there other MW102s that are dedicated bench models, or are these the ones you meant?

 

[ajdelange]

The MW102 is distinct from the others I mentioned in that it is not a 'pen' style meter. The 102 lies on the bench and a connected electrode is immersed in the samples. In the pen style the electrode is integral to the body of the meter. But it is certainly not so heavy or bulky one cannot carry it around.

 

[user 246304]

OK, gotcha. I think I was confused because I've seen people walking around with electrode styles, too. And I'm probably thinking of a permanently mounted, seriously expensive bench instrument, because that's what my friend had (I can't recall, unfortunately - I've been trying).

edit: I originally said "walking around with pen styles." I meant electrode, as you described, AJ.

 

[day_trippr]

fwiw, I've been using a Hach PocketPro+ for almost a year and it's been quite well behaved.
While its construction is fairly crude compared to the Hanna pHep98128 (also a "pen" style) that I've basically retired due to its calibration issues the Hach's performance has been very good.

Also fwiw, a friend brought over his Milwaukee O2 meter that from across the room appears physically identical to their pH meter. The probe and its extraordinarily oversized cable was a pita compared to a pen. (The meter wouldn't calibrate which is why it was brought to me but that's a whole 'nuther issue)...

Cheers!

 

[rhys333]

You have purchased a meter that is intended to be calibrated with NIST standard buffers. These are rarely used except in the laboratory. Most meters use NIST traceable 'operational' buffers. With them if the meter sees, during cal, a buffer near 7 it assumes it is a NIST traceable operational buffer and proceeds to do the calibration based on pH values for that meter stored in its memory. If you present such a buffer to your meter it will assume that it is a NIST buffer and proceed to calibrate presumably based on the tables for that buffer unless you tell it that the pH is something different which apparently you must do. Now what I can't tell from the manual is how this entry is treated with respect to temperature variation. Are you supposed to enter the pH of the buffer printed on the bottle label or the pH at the calibration table as obtained from the table often furnished with the buffer?

I would be a little skeptical about readings obtained with this meter (though the error is probably appreciably less than 0.1 pH) and would caution others to avoid it because of this.

It's not the ideal situation by any means but yes, you should do this. Better would be to buy NIST buffers (https://www.inorganicventures.com/productdisplay/ph-686-standard-0) and calibrate the meter as it is intended to be calibrated.

Thanks for explaining and sorry for my late response. I wanted to test this again on brew day before reporting back. I'm attaching images of the user manual pages which suggest to adjust calibration manually if the buffer solution isn't NIST. Today I tested it both ways. When I manually adjust the readout up to 7.02 (as per the table on the buffer solution) I get 5.49 on my wort sample. When I let the meter autocalibrate to 6.88 (NIST), I get 5.41 instead. A significant difference, however the meter locks in quickly each time and doesn't vary from these numbers. The meter seems to be reliable (or at least consistent), so I'll look into buying NIST 7.0 solution and until then continue adjusting to 7.02 as you suggest. I need to have another chat with the Thermoworks technician too.

View attachment 1506289228277.jpg

View attachment 1506289242215.jpg

 

[frettfreak]

Wow. Did not expect this much discussion on the topic but it has been a great lesson for sure! You guys are awesome!! Really appreciate all the input.

I think then, just for fun, I will do as AJ suggested and measure At mash temps, and a few on the way down to a room temp reading just to see what the slope is. Assuming (based on what I think I understood), the slope is going to change on every mash though, and this will not be for anything but interesting data.

FWIW, I have a blue labs bench style meter but am due for an upgrade (the pH resolution not good enough)... That new Hanna Halo looks light tempting! love the techie aspect of it all!!

 

[dantheman13]

There are some interesting claims in the recent BYO magazine in the "help me Mr. Wizard" section, which focuses on why they recommend taking mash pH readings at mash temperature. Obviously, I can't post the article here, but the author makes the claims that the sited literature collected by John Palmer has these values:

Bamforth's range: 5.3 to 5.8 (mash temp) / 5.55 to 6.05 (room temp)
Brigg's range: 5.2 to 5.4 (mash temp) / 5.45 to 5.65 (room temp)
Kunze's range: 5.25 to 5.35 (mash temp) / 5.5 to 5.6 (room temp)

I don't have access to the Bamforth or Kunze data, but I do have the Briggs data. The Briggs data is collected from various sources, and they make guesses as to what temperature the mash pH was taken in some of those data sets, so they are somewhat useless here.

The BYO article didn't look at Narziss's data, which Kai interprets as being taken at room temp:

http://braukaiser.com/wiki/index.ph...iency_in_single_infusion_mashing#mash_results

 

[Teesquar]

Dan, you beat me to it. I received my BYO mag yesterday and read through that article, thinking, "Great, more ranges to consider at mash and room temps".

Came back to this thread just as a reassurance and had to laugh at Silver's first line in post #4, "This issue seems to repeat itself periodically, and is often fueled by brewing magazine articles."

TBH, for a majority of my recipes, I'm just going to zone in on 5.4 and RDWHAHB

 

[Morrey]

Do some of the popular ph meters such as Hach Pocket Pro + take mash temp readings and adjust for temperature variations?

 

[ajdelange]

It has to get from mV to pH somehow. If it is a digital meter it does that by inserting mV into an equation. That equation needs to know slope, offset, temperature and isoelectric pH. If the meter has a temperature sensor (the Hach does) then it is using that to calculate slope and offset from temperature and known buffer pH's. It assumes isoelectric pH is 7.

Short answer: yes.