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pH readings

 
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KB




Joined: 06 Nov 2014
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Location: Virginia

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PostLink    Posted: Fri Dec 04, 2020 12:54 am    Post subject: pH readings Reply with quote


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I'm a bit confused by http://www.theelectricbrewery.com/forum/viewtopic.php?p=332561#332561 and then the reply http://www.theelectricbrewery.com/forum/viewtopic.php?p=332562#332562 in regard to taking a pH reading of the mash.

I thought the pH readings on a meter with ATC are taken at the same temp as the buffers used for calibration. If this is true/valid, then the wort sample should be cooled down (unless the buffers used for calibration were heated to our mash temp).

Please clarify as there are, as usual, conflicting info on this matter available from various brewing sites, forums, etc.

Thanks.
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kal
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Joined: 12 Dec 2010
Posts: 10804
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, London Pride, Wit, Janet's Brown, Russian Imperial Stout, Black Butte Porter

Working on: Belgian Quad, Belgian IPA


PostLink    Posted: Fri Dec 04, 2020 2:48 pm    Post subject: Reply with quote

No. There's no need to cool down the wort sample as long as you work with the caveats I outline in my Measuring pH guide: https://shop.theelectricbrewery.com/pages/measuring-ph

As per my guide, pH naturally change with temperature. As a solution increases in temp there is a chemical/energy change in the water that naturally makes a hotter solution more acidic (the pH is lower).

All that matters is that you follow the instructions for the 4/7 buffer solutions when you calibrate. Because of the fact I mentioned above the buffer solutions will *only* be at the pH stated on the bottle at the temperature the manufacturer states. This is why in my article I simply mention "To calibrate your pH meter follow the included instructions". For example, for the Hanna 4.01 buffer solution I show in the article it's written right on the bottle that it's pH 4.01 with an error of +/- 0.01 ph @ 25'C (77 F). That last part in bold is important. If it's not 25C/77F the buffer solution pH will not be 4.01.

Here's a closeup of the the 4.01 bottle that shows the writing on the bottle and box: https://cdn.shopify.com/s/files/1/2400/0975/files/4-00-pH-calibration-solution.jpg

If you heat up the 4.01 buffer solution to mash temp, it will no longer be 4.01 and your calibration will be off. So you can't do that. (Note: Don't worry about it being exactly at 25'C/77F when you calibrate - if your room temp is a few degrees off from that don't worry about it).

So make sure the follow the instructions for whatever buffer solution you use when calibrating.

Once calibrated, you can take pH readings at any temp you like (within the caveats I lay out in the article of course, and with the understanding the pH does naturally change with temp).

Good luck!

Kal

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Last edited by kal on Fri Dec 04, 2020 3:14 pm; edited 5 times in total
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kal
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Joined: 12 Dec 2010
Posts: 10804
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, London Pride, Wit, Janet's Brown, Russian Imperial Stout, Black Butte Porter

Working on: Belgian Quad, Belgian IPA


PostLink    Posted: Fri Dec 04, 2020 3:05 pm    Post subject: Reply with quote

You do raise a good point that I didn't realize may be confusing. So I've added some info to the instructions in the guide now to read:

"To calibrate your pH meter follow the included instructions. Given that pH naturally changes with temperature, calibration solutions will only be at their stated pH when at the temperature listed on the bottle so make sure to calibrate at (or near) that temperature. Normally this will be room temperature."

Room temp is chosen for the obvious reasons: There's nothing extra to do and less chance of error. Given the small amounts of calibration solution involved during a calibration, the temperature will change quickly if it's not at room temp. Could you imagine how hard it would be to calibrate if the solution was made to be used at (say) mash temp of 150-155F? Heating up and holding a small amount accurately while the calibration occurs would be difficult and require specialized heating equipment.

Kal

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KB




Joined: 06 Nov 2014
Posts: 272
Location: Virginia

Working on: Next brew


PostLink    Posted: Fri Dec 04, 2020 3:13 pm    Post subject: Reply with quote

I understand about calibrating at room temp. My question/confusion was in regard to taking a mash pH reading. Some say "Stick the pH meter in the mash" (or as I saw in a youtube video the person actually, mistakenly, dropped the whole pH meter in the mash and had to fish it out!), while others say to take a mash sample and cool to room temp (the same temp that was used to calibrate the pH meter).

Based on your reply, it seems to me, we calibrate at room temp and then take a reading of the mash pH by putting the probe into (the hot) mash then we need to add 0.2 to the pH reading to account for the temp difference between the room temp calibration and the temp of the mash. Is this correct?
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kal
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Joined: 12 Dec 2010
Posts: 10804
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, London Pride, Wit, Janet's Brown, Russian Imperial Stout, Black Butte Porter

Working on: Belgian Quad, Belgian IPA


PostLink    Posted: Fri Dec 04, 2020 3:41 pm    Post subject: Reply with quote

KB wrote:
Based on your reply, it seems to me, we calibrate at room temp...

Not entirely correct. We calibrate at whatever temperature is mentioned on the calibration solution bottles and with the instructions. This will usually always be room temp for the reasons stated above. It's probably a pretty safe bet it's always going to be room temp but I'd still double check.

KB wrote:
...and then take a reading of the mash pH by putting the probe into (the hot) mash...

If your meter has ATC you can do that (both listed in my guide do have ATC). If you use something else, follow the instructions on the specific pH meter you're using (if your meter doesn't have ATC it'll usually mean you have to cool the sample first).

KB wrote:
...then we need to add 0.2 to the pH reading to account for the temp difference between the room temp calibration and the temp of the mash. Is this correct?

The reason for the 0.2 offset has nothing to do with the temperature at which you calibrated. Calibration is completely separate from taking actual readings. You don't care at what temp you calibrated when it comes to using the meter in the future.

Assuming your pH meter has ATC, ATC only compensates for the change in the electrical response of the pH meter probe with temperature. It does not compensate for the chemical/energy change in the water that naturally makes a hotter solution more acidic (lower pH). What this amounts to at the end of the day is that at mash temperature pH is approximately 0.2 lower than at room temperature. That's where the offset comes from. Nothing to do with calibration.

ut whether to need to add 0.2 or take away 0.2 from your reading depends entirely on what you're targeting. Remember that pH changes with temp so every single pH number anyone lists has to always indicate also at what temp they want that pH, otherwise you have no idea what they mean. For example, if someone tells you "get your mash to a pH of 5.2 @ 150F" and you stick your pH meter with ATC directly in the mash and take a reading at 150F, you don't need to add or remove anything from what your pH meter reports to compare against the 5.2 target since both the target and the reading are the same temp (150F). But if someone says "get your mash to a ph of 5.4 @ 75F" and you take a reading again directly in the 150F mash, you need to account for the fact that your mash at 150F is hotter than the 75F expected temp so 5.4 is not the reading you will be expecting from your meter. A hotter liquid has a lower pH (approx 0.2 lower at mash temp than room temp) so you want to see 5.2 on your meter instead of 5.4 for them to be the "same" pH.

So you can't just blindly add or remove 0.2. It depends on the target pH temp and at what temp you measure. It's relative. Context matters.

Again, at what temp the calibration solutions make you calibrate has nothing to do with how you use the meter after.

Cheers!

Kal

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KB




Joined: 06 Nov 2014
Posts: 272
Location: Virginia

Working on: Next brew


PostLink    Posted: Fri Dec 04, 2020 3:50 pm    Post subject: Reply with quote

OK. Thanks. Internet is good for some things and bad for other things, especially trying to learn, there are many conflicting opinions on this topic. I want to ensure I'm doing things correctly.

Some state using the pH meter directly in the hot mash will shorten the pH probe life. However, the instructions for my pH meter, the Milwaukee MW102, indicates the temp range is -5.0 to 105C (23 to 221F) so I believe I am OK directly using the MW102 pH probe in the mash unless, as I've read bits of malt may throw off the reading. If so, then probably best to get only a liquid sample from the mash and then take the pH reading.


Last edited by KB on Fri Dec 04, 2020 8:39 pm; edited 1 time in total
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kal
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Joined: 12 Dec 2010
Posts: 10804
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, London Pride, Wit, Janet's Brown, Russian Imperial Stout, Black Butte Porter

Working on: Belgian Quad, Belgian IPA


PostLink    Posted: Fri Dec 04, 2020 4:13 pm    Post subject: Reply with quote

KB wrote:
Some state using the pH meter directly in the hot mash will shorten the pH probe life.

That is true. I cover that in my BREW DAY STEP BY STEP and my thoughts on it:

https://shop.theelectricbrewery.com/pages/brew-day-step-by-step#STEP_5_Mash

Quote: "The pH meter probe electrode will last longer if the sample is first cooled to room temperature, but ours (so far) has last 10 years when brewing once or twice a month, so we've never bothered cooling down a sample as it's much quicker. Feel free to cool a sample to room temperature if you prefer, or if your pH meter's maximum temperature compensation is considerably lower than the temperature you're measuring at."

So up to you.

Quote:
However, the instructions for my pH meter, the Milwaukee MW102, indicates the temp range is -5.0 to 105C (23 to 221F)

That range is not correct. The probe tips are fragile. I've never heard of any that can go above boiling like that.

In fact, their website had conflicting information back when I was researching my guide so I ended up talking to their engineers who mentioned that the temp ranges listed varied depending on what you were using since the MW102 has separate probes for pH and temp. Their website stats list the following conflicting info:

Temp Range: -5 to 70C (158F)
Temperature Compensation: Automatic, 0 to 70C (158F)
Environment: 0 to 50C / 32 to 122F

My questions to them were around the 158F and 122F difference.

Here's the correct information from them that I have in my guide: "... automatic temperature compensation up to 122F. The temperature probe can read slightly higher temperatures, up to 158F..."

They admitted the temp compensation high temp (158F) listed is wrong. I see they still haven't updated their website.

Quote:
so I believe I am OK directly using the MW102 pH probe in the mash unless, as I've read bits of malt may throw off the reading.

Above 122F the temp compensation is no longer as accurate, and the higher the temp, the faster you will shorten the life of the probe. Temp compensation issues aside, you can certainly put a probe in a hot solution but you seem to be implying that as long as you're anywhere within the manufacturer acceptable range that the probe will degrade at the same rate. That is not correct. Higher temps will dissolve the probe tip faster.

Cheers!

Kal

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KB




Joined: 06 Nov 2014
Posts: 272
Location: Virginia

Working on: Next brew


PostLink    Posted: Fri Dec 04, 2020 4:32 pm    Post subject: Reply with quote

Hmm... I wonder what else in the MW102 user manual is incorrect. I just received the unit yesterday.

I did a quick search online. I believe this has the same specs as the manual I received.
http://milwaukeeinstruments.com/content/manuals/manMW102_ENG.pdf

And then I note the specs here don't totally match the user manual included with the MW102!
http://milwaukeeinstruments.com/milwaukee-MW102-pro-ph-meter-with-temperature-probe/#product-specifications
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kal
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Joined: 12 Dec 2010
Posts: 10804
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, London Pride, Wit, Janet's Brown, Russian Imperial Stout, Black Butte Porter

Working on: Belgian Quad, Belgian IPA


PostLink    Posted: Fri Dec 04, 2020 7:10 pm    Post subject: Reply with quote

No idea. That 122F / 158F discrepancy was the only one that stood out for me given that the specs had conflicting information so that's why I asked their engineers. That said, it's a very highly regarded unit by brewers (if you read/follow brewing articles and talk to other brewers) and that's why it's in my article and recommended. If I had to buy again today it's probably what I'd get.

Shameless plug: If anyone wants to purchase one and help support us at no extra cost to them, they can do so here: https://shop.theelectricbrewery.com/pages/milwaukee-mw102-ph-meter

Cheers!

Kal

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Our new shop with over 150 new products: shop.TheElectricBrewery.com
We ship worldwide and support our products and customers for life.
Purchasing through our affiliate links helps support our site at no extra cost to you. We thank you!
My basement/bar/brewery build 2.0


Last edited by kal on Fri Dec 04, 2020 8:45 pm; edited 1 time in total
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KB




Joined: 06 Nov 2014
Posts: 272
Location: Virginia

Working on: Next brew


PostLink    Posted: Fri Dec 04, 2020 8:36 pm    Post subject: Reply with quote

Kal, thanks for the clarification and input. I look forward to using my new pH meter next brew day.
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kal
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Joined: 12 Dec 2010
Posts: 10804
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, London Pride, Wit, Janet's Brown, Russian Imperial Stout, Black Butte Porter

Working on: Belgian Quad, Belgian IPA


PostLink    Posted: Fri Dec 04, 2020 8:45 pm    Post subject: Reply with quote

Enjoy!

Kal

_________________
Our new shop with over 150 new products: shop.TheElectricBrewery.com
We ship worldwide and support our products and customers for life.
Purchasing through our affiliate links helps support our site at no extra cost to you. We thank you!
My basement/bar/brewery build 2.0
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mjo2125




Joined: 27 Feb 2017
Posts: 249
Location: Dayton, OH

Drinking: Pale Ale, Yorkshire Bitter, Mango Blonde Ale

Working on: Retro American Lager


PostLink    Posted: Sat Dec 05, 2020 2:58 am    Post subject: Reply with quote

Yep I asked Milwaukee Inst. the same question about the temperature range discrepancy but didn't get a response. I bought one anyway a few days ago as a replacement for my Hanna pH meter (board shorted out according to customer service) after a couple of years.
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