Author Topic: Is pH stated at room temperature or operating temperature?  (Read 1822 times)

Offline malzig

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Re: Is pH stated at room temperature or operating temperature?
« Reply #15 on: May 07, 2011, 08:00:39 AM »
I don't see any reason or advantage to testing at mash temperature, other than not having to cool the sample.  The target of 5.4 - 5.6 was established at room temp.

If you're using ColorpHast pH strips, they seem to give the same pH at mash temp as at room temp, so you still want to use the 5.4-5.6 range.

Yes, but to confuse things even more they also seem to skew a little bit low, so you can aim for 5.1 - 5.3  :)

Kai's evaluation of ColorpHast pH strips.
Very true and important, I should have mentioned that ColorpHast strips have been found to read about 0.3 low in the mash pH range.

Offline Tristan

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Re: Is pH stated at room temperature or operating temperature?
« Reply #16 on: May 18, 2011, 12:10:22 PM »
So to take this one step further, if I test the pH of the mash at mash temp (~150) and obtain a reading of 5.0 it's roughly equivalent to a pH of 5.5 at room temp (.3 from the inherent error of the strip and .2 for the temp shift)?  So I'd shoot for a reading on the ColorPhast strip of 4.8 - 5.0 at mash temps or do I have this backwards?
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Offline malzig

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Re: Is pH stated at room temperature or operating temperature?
« Reply #17 on: May 18, 2011, 06:50:15 PM »
So to take this one step further, if I test the pH of the mash at mash temp (~150) and obtain a reading of 5.0 it's roughly equivalent to a pH of 5.5 at room temp (.3 from the inherent error of the strip and .2 for the temp shift)?  So I'd shoot for a reading on the ColorPhast strip of 4.8 - 5.0 at mash temps or do I have this backwards?
No.  There's a temperature dependent change in the chemical reaction that produces color on these strips that causes them to read the same at mash temperature as they do at room temperature.

Offline hokerer

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Re: Is pH stated at room temperature or operating temperature?
« Reply #18 on: May 18, 2011, 07:09:19 PM »
yep, just look at is as .3 inherent error and .3 temp shift.  The .3's are in opposite directions so they cancel each other out.
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Offline Tristan

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Re: Is pH stated at room temperature or operating temperature?
« Reply #19 on: May 19, 2011, 08:09:52 AM »
Good deal!  So on the strips at mash temp I'm still looking for a value of 5.2 - 5.5?  I might be thinking a bit to hard on this one.
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Offline nyakavt

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Re: Is pH stated at room temperature or operating temperature?
« Reply #20 on: May 20, 2011, 10:40:14 AM »
Quote
Good deal!  So on the strips at mash temp I'm still looking for a value of 5.2 - 5.5?  I might be thinking a bit to hard on this one.

You still want to shoot for 5.1-5.3 on the colorpHast strips regardless of the temp reading (I shoot for 5.0-5.3, which are the strip markings).  The decrease in pH of the solution due to increased temp is offset by an increase in apparent reading on the strip due to the chemical reaction of the litmus paper being affected by temperature.  The -0.3 systematic error inherent to the strips is still present and must be accounted for.  Also be aware that with darker beers the wort color can affect the color of the strip, so make sure to dab it with a towel before trying to read.

Offline mabrungard

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Re: Is pH stated at room temperature or operating temperature?
« Reply #21 on: May 20, 2011, 10:54:12 AM »
yep, just look at is as .3 inherent error and .3 temp shift.  The .3's are in opposite directions so they cancel each other out.

Uh...I don't use the strips since I have a meter and the fact that they have proven to be inaccurate in the mash, but I don't think the temp shift enters into this issue.
 
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Offline Tristan

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Re: Is pH stated at room temperature or operating temperature?
« Reply #22 on: May 22, 2011, 07:42:05 AM »
You still want to shoot for 5.1-5.3 on the colorpHast strips regardless of the temp reading (I shoot for 5.0-5.3, which are the strip markings).  The decrease in pH of the solution due to increased temp is offset by an increase in apparent reading on the strip due to the chemical reaction of the litmus paper being affected by temperature.  The -0.3 systematic error inherent to the strips is still present and must be accounted for.  Also be aware that with darker beers the wort color can affect the color of the strip, so make sure to dab it with a towel before trying to read.

Thanks!  This is helpful info!
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Offline malzig

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Re: Is pH stated at room temperature or operating temperature?
« Reply #23 on: May 22, 2011, 05:50:29 PM »
yep, just look at is as .3 inherent error and .3 temp shift.  The .3's are in opposite directions so they cancel each other out.
Uh...I don't use the strips since I have a meter and the fact that they have proven to be inaccurate in the mash, but I don't think the temp shift enters into this issue.
That's quite an oversimplification.  If you correct for the pH shift at room temperature, ColorpHast strips are both accurate and precise.

If you don't calibrate a pH meter you'll get the wrong pH measurement, but that doesn't make it inaccurate.

Like any tool, you need to know how to use it.

Offline euge

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Re: Is pH stated at room temperature or operating temperature?
« Reply #24 on: May 22, 2011, 07:33:24 PM »
My Brown ale's mash was 5.2 pH @ 80F on Friday. I'm assuming it was in range.  Just check the pH to make sure the mash isn't off. If it was off I don't have anything food-grade to drop it but I could raise it with some bicarb. 
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Offline johnf

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Re: Is pH stated at room temperature or operating temperature?
« Reply #25 on: May 22, 2011, 09:45:09 PM »
yep, just look at is as .3 inherent error and .3 temp shift.  The .3's are in opposite directions so they cancel each other out.
Uh...I don't use the strips since I have a meter and the fact that they have proven to be inaccurate in the mash, but I don't think the temp shift enters into this issue.
That's quite an oversimplification.  If you correct for the pH shift at room temperature, ColorpHast strips are both accurate and precise.

If you don't calibrate a pH meter you'll get the wrong pH measurement, but that doesn't make it inaccurate.

Like any tool, you need to know how to use it.

How precise? The design precision is .3 pH. That is not as precise as even a very inexpensive meter.

As for accuracy, they measure .3 low at reference temperature, compared to a calibrated meter at reference temperature.

This isn't a temperature issue, they are just wrong in mash, for whatever reason.

Offline malzig

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Re: Is pH stated at room temperature or operating temperature?
« Reply #26 on: May 23, 2011, 04:32:50 AM »
How precise? The design precision is .3 pH. That is not as precise as even a very inexpensive meter.

As for accuracy, they measure .3 low at reference temperature, compared to a calibrated meter at reference temperature.

This isn't a temperature issue, they are just wrong in mash, for whatever reason.
So the pH meter makes an electronic correction for it's inaccuracy and you have to make a minor mental correction.  After that correction they are both accurate.  Besides, it's pretty easy to get a bad reading from a pH meter in complex solutions like a mash.  Some pH meters don't handle ions as simple as sodium very well, let alone complex species like proteins.  Two calibrated pH meters can easily differ by 0.3-0.6 when measuring the same solution.  Don't be fooled into thinking that, just because you get a digital readout that you know the exact pH of the mash.  You really have no idea if the pH is 5.3 when the meter says 5.3.

The strips will tell you that the mash pH is between 5.3 and 5.6.  When the color is between those two spots you can assume it's closer to 5.4-5.5.  I think that's an appropriate precision for brewing, which you may not.