Best time to measure mash Ph?

[Larso]

Hi, I brew with RO water. I've been using AJDs brewing water chemistry primer to adjust my water adding only CalciumSulphate,CalciumChloride and acid malt. Recently I bought a Ph meter and started using EZWater calculator to estimate mash Ph. I BIAB and I wrap the mash heavily so I only really want to take th emash Ph once. On the first brew I took it at the end of a 90min mash and it matched the calculator exactly--very impressed! I dont intend adjusting mash Ph, I just want to be able to accurately predict it and compensate with changes on the next brew if i have to.
How does mash Ph progress over the course of the 90/60min mash(or does it change at all significantly after it stabilises)? Does it make sense to just measure it at the end of mash?

Thanks

L

 

[ajdelange]

When using acid malt I have found that the pH initially plummets as, I suppose, acid from the surface of the sauermalz grain is washed off into solution. Then over time it rises, pretty rapidly at first and then more slowly. By 30 minutes or so the readings seem to be stable. In measuring the buffering capacities of malt the pH also tends to rise over about 30 minutes. So I'd say 30 minutes in is a good time to measure if you are confident and are just doing a check. If you are thinking of adjustments an earlier measurement at say 10 minutes, while not stable, should give you some idea as to whether you have over or undershot.

 

[Larso]

When using acid malt I have found that the pH initially plummets as, I suppose, acid from the surface of the sauermalz grain is washed off into solution. Then over time it rises, pretty rapidly at first and then more slowly. By 30 minutes or so the readings seem to be stable. In measuring the buffering capacities of malt the pH also tends to rise over about 30 minutes. So I'd say 30 minutes in is a good time to measure if you are confident and are just doing a check. If you are thinking of adjustments an earlier measurement at say 10 minutes, while not stable, should give you some idea as to whether you have over or undershot.

Thanks AJ, would you expect a 30minute sample to be at the same(or close) ph to a 60/90min sample?

 

[ajdelange]

Yes. I don't find much change beyond 30 min unless a decoction has been pulled, processed and returned.

 

[jtlambert]

what ph meter are you guys using? does it compensate for mash temps?

 

[ajdelange]

I'm using a Hach laboratory pH meter which it is very unlikely that you would consider buying. Like all digital meters it is capable of ATC (Automatic Temperature Compensation) but ATC does not compensate for mash temperature. See https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ under 'ATC -What is it' for details.

 

[jtlambert]

I bought a Hanna 98127 Which I will be using for the first time today. I'm brewing a pumpkin ale.
I was under the impression that it would compensate for mash temperatures. I will check out the link

 

[ajdelange]

No, only its electrode's temperature response. This is a common misconception.

 

[mabrungard]

ATC is useless when used at typical mashing temperatures. It only corrects for the minor pH reading errors that are a result of the probe's response. Get the word out, mash pH measurement that is not made near room temperature is likely to be inaccurate and ATC can't fix it.

 

[ajdelange]

We need to be a little careful here. ATC is essential if a pH measurement is made at mash temperature unless the electrode was calibrated with buffers that were also at mash temperature. This is actually the better practice if readings are made at mash temperature as if the buffers are measured at room temperature and the sample at another temperature ATC will introduce errors if the isoelectric pH (pHi) of the electrode isn't 7 (which it should be but that doesn't mean it is). No demands are placed on ATC if buffers and samples are at the same temperature and that is the best way to do things or have them close to the same temperature so that even if pHi ≠7 the error caused by this is small. But let me repeat that all reported measurements in brewing these days are room temperature measurements and room temperature measurements insure long electrode life.

Measurements made at mash temperature are accurate whatever pHi if the buffers were also measured at mash temperature and are also accurate if the buffers were measured at room temperature and pHi is close to 7. And the same is true of measurements made at room temperature. The problem is that we aren't interested in the room temperature pH of the mash because that is not the temperature at which the enzymes work their magic. We only use room temperature because if we measured at mash temperature there would be a question as to which mash temperature we should measure at (beta glucan rest, protein rest, low saccarification rest...) and it would effect the lives of our electrodes. Thus while properly made room temperature measurements may accurately reflect the pH of the wort at room temperature they do not accurately reflect the pH in the actual mash. We can estimate what that may be by multiplying the temperature difference by 0.0055 and subtracting that from the room temperature reading but that is only an estimate. Other workers have posted other rates of change dependent on water chemistry, among other things. The only way to know for sure is to measure at mash pH.

But what we are doing is OK. If the mash pH falls in a certain range at room temp. the beer will be OK. It is akin to the practices pilots follow with respect to altitude. Every pilot in a region sets his altimeter to a published 'altimeter setting'. Unless the altimeter setting reflects the actual meteorological conditions where the plane actually is (and it doesn't) the altimeter does not read actual altitude but everyone whose altimeter says 2500 ft is at the same altitude and that's good enough to keep the planes from flying into one another.

 

[jtlambert]

Wow there is a lot to this. So if I understand correctly the best practice is to calibrate the pH meter with 4.01 & 7 buffer at approximately 150°?
Then measurements taken at that same temp will be accurate? Am I also correct to understand that this will lessen the life of the pH electrode?

 

[Yooper]

Wow there is a lot to this. So if I understand correctly the best practice is to calibrate the pH meter with 4.01 & 7 buffer at approximately 150°?
Then measurements taken at that same temp will be accurate? Am I also correct to understand that this will lessen the life of the pH electrode?

No, don't do that! Sure, it'd be accurate, as AJdeLange explained, but it will trash your electrode. And they are expensive to replace!

Calibrate your meter at room temperature, and cool your mash sample to the same temperature.

 

[ajdelange]

Wow there is a lot to this. So if I understand correctly the best practice is to calibrate the pH meter with 4.01 & 7 buffer at approximately 150°?

That might be the best practice but that is NOT what you want to do! For two reasons:

Am I also correct to understand that this will lessen the life of the pH electrode?

1. Yes, that is right. It will shorten the life of your electrode
2. No one else does this (except researchers) so that all your numbers will be noticeably lower than other peoples', the recommendations given here and elsewhere, articles, textbooks etc.

I can't say it better than Yooper did but I can say it again just so it is very clear:

Calibrate your meter at room temperature. Cool your samples to room temperature and measure them at room temperature.

Note: the temperature of the samples and buffers do not have to be exactly the same (and the temperatures of the buffers can be different from one another too) but the less temperature difference there is the less ATC has to do and the less the sensitivity of your measurements to error in isoelectric pH.

 

[jtlambert]

So best practice is to measure at room temp (after the mash) and see if you were close to what you were shooting for? And adjust for next brew?

I was kinda hoping to get a reading, and make adjustments on the fly if necessary.

For the pumpkin ale I ended up getting a pH of 5.6 in a sample taken 15 min into mash & another taken 30 min into mash (both samples read at room temp (74 degrees) hours later)
That was dead on from what EZ Calculator 3.0.2 calculated from grain bill, water & salt additions.

 

[ajdelange]

So best practice is to measure at room temp

Yes.

(after the mash) and see if you were close to what you were shooting for?

No, during the mash. Withdraw a sample at 10 minutes and put it in a shot glass taken out of the freezer or a very small metal pot which you then immerse in cold water. Or get the mash sample to room temperature quickly by any other means. If the pH is way off take action. If it is a little off take another sample at 20 minutes and repeat. If this sample is too high or low then take action. We hope that your readings will be close enough that you will

...adjust for next brew

that is, that these measurements, while not spot on will be close enough that things work out and you can make fine adjustments the next time.

I was kinda hoping to get a reading, and make adjustments on the fly if necessary.

If you are willing to take the time before the brew (say the night before) to make a small test mash, check its pH and adjust it to the desired value then scale the acid/base additions to the size of the full mash and apply them to the full mash when it is carried out you should be pretty close. You should be in the close enough to tweak on the next brew regime.

For the pumpkin ale I ended up getting a pH of 5.6 in a sample taken 15 min into mash & another taken 30 min into mash (both samples read at room temp (74 degrees) hours later)

Though you might want to be 0.1 lower than this 5.6 is fine and you should conclude that you hit the target pretty close to the bulls eye. If you want to adjust windage a bit for the next shot (the next time you brew this beer) add a bit more sauermalz (an extra 1% by weight) or its equivalent in lactic or whatever other acid you are using.

 

[bob1852]

How much does time affect pH?

Lately I've been lazy and will take a post-mash, sparge, pre-boil, and post-boil pH samples in a shot glass, cover it with foil so evaporation doesn't concentrate it; and take the pH after the brew session is over and the samples have cooled down to room temp on their own.

So, the mash pH sample is maybe sitting for ~2-2.5 hours.

 

[ajdelange]

See #2.

 

[jtlambert]

Thanks for all the info guys, I appreciate it. Very helpful.