Is there a way to test a pH probe?

[raysmithtx]

This is kind of long because of the level of detail...

I use Brun water and in the beginning always tested the mash pH. After many batches I decided that Brun water was pretty darn close and the pH testing was not necessary.

Fast forward to my last couple of brews and I decided to check the mash pH again. I don't know why. Maybe the pH meter just looked lonely in the tub as I was brewing.

I always calibrate the pH meter with both 7.0 and 4.0 solution. I use RO water and use a diluted 20% solution of Phosphoric Acid to reduce the pH. Both of the the batches showed my pH low. One was supposed to be 5.4 and it measured 5.1. Today the pH was supposed to be 5.4 and it measured 5.04. Really low.

I went back and triple checked the grain bills and volumes in Brun water and they are all correct. I checked the Specific gravity of my Phosphoric acid 20% solution with my hydrometer and read 1.118 at 55 degrees which correlated to a 20% solution. I checked my RO water TDS and it reads 11 (ideal according to the meter). Which leads me to believe my pH probe may be the problem. I always store it in storage solution and it has never dried out. I bought the unit Milwaukee MW102 in July of last year so the probe and meter are only 9 months old.

So after all this, is there a way to confirm that the probe is the problem? I'm guessing it could be the probe or the meter.

 

[fun4stuff]

This is kind of long because of the level of detail...

I use Brun water and in the beginning always tested the mash pH. After many batches I decided that Brun water was pretty darn close and the pH testing was not necessary.

Fast forward to my last couple of brews and I decided to check the mash pH again. I don't know why. Maybe the pH meter just looked lonely in the tub as I was brewing.

I always calibrate the pH meter with both 7.0 and 4.0 solution. I use RO water and use a diluted 20% solution of Phosphoric Acid to reduce the pH. Both of the the batches showed my pH low. One was supposed to be 5.4 and it measured 5.1. Today the pH was supposed to be 5.4 and it measured 5.04. Really low.

I went back and triple checked the grain bills and volumes in Brun water and they are all correct. I checked the Specific gravity of my Phosphoric acid 20% solution with my hydrometer and read 1.118 at 55 degrees which correlated to a 20% solution. I checked my RO water TDS and it reads 11 (ideal according to the meter). Which leads me to believe my pH probe may be the problem. I always store it in storage solution and it has never dried out. I bought the unit Milwaukee MW102 in July of last year so the probe and meter are only 9 months old.

So after all this, is there a way to confirm that the probe is the problem? I'm guessing it could be the probe or the meter.

Aside from checking it with fresh calibration solutions (e.g. 4 and 7), you could test if against things of known pH (e.g. 5% vinegar). If the pH meters reads 4 and 7 when in those solutions which are freshly made with distilled water, then I would think the meter is working correctly.

 

[cannman]

How you crush your grain can also mildly change your ph. Perhaps you need to ease up on the grind/crush (meaning the readings are accurate). Also don't forget temp affects ph

https://www.quora.com/How-does-temperature-affect-the-pH-of-liquids

 

[mabrungard]

The other consideration should be that the acidity of one or more of your grains has changed. I've heard of several cases where the base malt acidity has changed. There have been other cases where the strength of acid malt varied. Another cause could be that your water supply has more dissolved CO2 than previous. Excess CO2 can drive down water pH as carbonic acid.

While a brewing water chemistry program can help get your pH close, there are still plenty of reasons to verify pH results.

 

[ajdelange]

If you will go to the top of the Brewing Science thread you will find Stickies. These are posts which address commonly asked questions and are there so that the people who know the answers to these questions don't have to type the same answer over and over. Yours is a commonly asked question and there is, therefore, a sticky which addresses it at https://www.homebrewtalk.com/showthread.php?t=302256. In essence if your pH meter can pass the stability test then it is not the meter. Meters do occasionally come in out of left field and eventually the electrode life ends. If your meter displays slope and offset during calibration jot those down in your log and use that data to monitor the ageing of your electrode. If you see a suspicious pH reading the first thing to do is rinse it off and put it into fresh pH 4 buffer. If it reads something other than very close to 4 recal and try again.

An algorithm that attempts to tell you what your mash pH is going to be must, explicitly or implicitly, estimate that as the pH which causes the sum of the proton deficits of all the mash components to be exactly 0. To do that accurately it must know the proton deficit of each component, including the malts, accurately. There is really no way a program can obtain that data unless someone measures it and enters it into the program. We can hardly expect a program to be able to accurately know a particular malt's parameters based on its type or color or anything other than measurement. THe programs make lots of simplifying assumptions. Which ones, for example, ask for the moisture content of the malts. If a kg of Maris Otter has buffering of 50 mEq/kg•pH on a dry basis it has buffering of 47.5 at moisture content of 5%.

Measurement shows, for example, that Crisp Maris Otter and Munton Maris Otter are quite different (their buffering capacities are very similar but one has a DI mash pH amost 0.2 pH higher than the other). What this means is that if your program doesn't distinguish between the two it can't give you an accurate pH estimate. Even if you have a program that explicitly and robustly processes the malt data (there aren't any) and knows the difference between Munton's and Crisp you are out of luck if using Fawcetts MO. Then there is variation between season, lot number etc. I'm trying to get maltsters to put the info on the bag or at least in the CMAs but they aren't too interested.

Even considering all this there is enough similarity between malts of a given kind that one can often get a pH estimate that is pretty good but even with the robust approach errors of 0.1 - 0.2 and a bit more are not uncommon but 0.3 - 0.4 often turns out to be a data entry problem.

Use calculations for guidance but rely on your verified pH meter as the final determinant as to whether you have hit pH or not.

 

[raysmithtx]

If you will go to the top of the Brewing Science thread you will find Stickies. These are posts which address commonly asked questions and are there so that the people who know the answers to these questions don't have to type the same answer over and over. Yours is a commonly asked question and there is, therefore, a sticky which addresses it at https://www.homebrewtalk.com/showthread.php?t=302256.

My question wasn't about calibrating the meter. It calibrates just fine in both of the solutions but thanks for the link. It confirms that I am calibrating the meter properly.

How you crush your grain can also mildly change your ph. Perhaps you need to ease up on the grind/crush (meaning the readings are accurate). Also don't forget temp affects ph

https://www.quora.com/How-does-temperature-affect-the-pH-of-liquids

I crush my own grains and haven't changed anything so I don't think that's the issue and I measured the pH at a reasonable temp. (60 degrees)

It's nice how some people try to be helpful on this forum.

I ordered a new probe yesterday which will hopefully fix the problem.

 

[cannman]

I crush my own grains

This is what I was getting at. Adjust how you crush, and see if that changes the ph for you

 

[ajdelange]

So after all this, is there a way to confirm that the probe is the problem? I'm guessing it could be the probe or the meter.

Yes, and it is described in the sticky the first few paragraphs of which talk about calibration and the latter of which talk about a stability test which confirms proper operation (or not) of the meter. You have to read (or at least skim) the whole piece to know what is in it.

 

[raysmithtx]

Just an update. After multiple emails from Milwaukee Instruments they determined that the meter is bad. Not the pH probe and not the temperature probe, the meter itself.

It's on it's way back to them now for repair/replacement.