Author Topic: Correctly reading ph test strips  (Read 4701 times)

Offline hokerer

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Correctly reading ph test strips
« on: January 09, 2010, 04:48:41 PM »
Ok, I've seen all the discussion about the difference between ph at mash temp and at room temp... also the discussion of the test strips reading about 0.3 hi/lo.  And now I'm confused.

I wait at least 10 minutes after dough-in, collect a small sample that is, as much as possible, just liquid, let it cool to ambient temp, and then check it with the test strip.  Say I read 5.8.  Does that mean the mash ph was 5.5? (subtract 0.3 for temperature)...  or was it 5.2? (subtract 0.3 for temp and another 0.3 for strip inaccuracy)... or was it 5.8? (subtract 0.3 and then add 0.3)...  or am I adding when I should be subtracting or what?

Also, if ph differs at the different temperatures, when they say 5.2 is ideal, what temp is that at?
Joe

Offline lupy

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Re: Correctly reading ph test strips
« Reply #1 on: January 09, 2010, 11:36:54 PM »
I claim no first hand knowledge but according to Kai;
"In the end it was confirmed that the colorpHast strips have a -0.3 systematic error when they are used for testing the mash pH." "I.e. the strips tend to report a pH reading that is about 0.3 pH less than what is determined with a calibrated pH meter"
http://braukaiser.com/wiki/index.php?title=An_Evaluation_of_the_suitability_of_colorpHast_strips_for_pH_measurements_in_home_brewing
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Offline hokerer

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Re: Correctly reading ph test strips
« Reply #2 on: January 10, 2010, 12:46:02 PM »
"I.e. the strips tend to report a pH reading that is about 0.3 pH less than what is determined with a calibrated pH meter"

Ok, got that part.  So above, when I read 5.8 with the strip, that really means 6.1?  Still leaves what do I do about the temp?  The ph at mash temp is supposedly 0.3 off from the ph at ambient.  Do I add or subtract 0.3?  Ultimately, I guess I want to find out how from the magical 5.2 I am so I can see which direction to adjust things, right?
Joe

Offline a10t2

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Re: Correctly reading ph test strips
« Reply #3 on: January 10, 2010, 02:32:44 PM »
Mash pH readings are (or at least should be) reported with the assumption that the sample is cooled. So you want to read roughly 5.5 at room temp, which is about 5.2 at mash temp.

Of course, for your own measurements you can do it either way, as long as you're consistent.
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Offline brewbeard

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Re: Correctly reading ph test strips
« Reply #4 on: January 10, 2010, 07:02:54 PM »
To make things more confusing, the ColorpHast strips are not affected by temperature. For some reason, the will always read a room temperature pH. A strip dipped in the mash at room temperature and at mash temperature will look exactly the same. Kai noticed this, I tried it for myself and noticed the same thing.


Essentially follow this with the ColorpHast strips:

Regardless of the temperature, try to target a pH between 5.1 and 5.4 on the strip.


You can just dip the pH strip in the mash and take a reading. Adjust if it looks like it is out of this range.

Offline Kaiser

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Re: Correctly reading ph test strips
« Reply #5 on: January 10, 2010, 07:04:07 PM »
The aforementioned article is still under construction because I'm planning to add exactly that. But based on my obsevations so far, the pH strip reading is independent of mash temp. That means: even a strip placed in a hot mash will give a reading that is about 0.3 lower than the mash's room temp pH.

I plan to take some pictures but haven't gotten around to that yet.

Kai

Offline hokerer

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Re: Correctly reading ph test strips
« Reply #6 on: January 10, 2010, 08:23:16 PM »
will give a reading that is about 0.3 lower than the mash's room temp pH.

So since that is room temp pH and mash temp pH is about 0.3 lower than room temp pH does that mean that the reading on the strip ends up being equal to the mash temp pH?  and it's the mash temp pH that we're targeting to be 5.2?
Joe

Offline Kaiser

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Re: Correctly reading ph test strips
« Reply #7 on: January 10, 2010, 08:59:03 PM »
I don't exactly know where this 5.2 mash pH target comes from. The literature I read indicates that 5.4-5.6 is a better target. Those numbers, however, are for room temp samples.

Kai

Offline Thirsty_Monk

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Re: Correctly reading ph test strips
« Reply #8 on: January 11, 2010, 10:52:41 AM »
A strip dipped in the mash at room temperature and at mash temperature will look exactly the same. Kai noticed this, I tried it for myself and noticed the same thing.


Essentially follow this with the ColorpHast strips:

Regardless of the temperature, try to target a pH between 5.1 and 5.4 on the strip.


You can just dip the pH strip in the mash and take a reading. Adjust if it looks like it is out of this range.

Strip dipped into boiling wort will ehmm... melt.  :-[ Ask me how I know.
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Offline tygo

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Re: Correctly reading ph test strips
« Reply #9 on: January 13, 2010, 10:35:40 AM »
I don't exactly know where this 5.2 mash pH target comes from. The literature I read indicates that 5.4-5.6 is a better target. Those numbers, however, are for room temp samples.

Kai

So if 5.4 - 5.6 is the target, and that's at room temperature, then the pH at mash temperature that's being targeted is 5.1 - 5.3.  Is that right?
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Offline ndcube

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Re: Correctly reading ph test strips
« Reply #10 on: January 13, 2010, 10:50:06 AM »
I don't exactly know where this 5.2 mash pH target comes from. The literature I read indicates that 5.4-5.6 is a better target. Those numbers, however, are for room temp samples.

Kai

So if 5.4 - 5.6 is the target, and that's at room temperature, then the pH at mash temperature that's being targeted is 5.1 - 5.3.  Is that right?

That's my understanding.  So the buffer 5.2 product should bring your pH to 5.5 at room temp...

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Re: Correctly reading ph test strips
« Reply #11 on: January 13, 2010, 10:56:55 AM »
So the buffer 5.2 product should bring your pH to 5.5 at room temp...

It should, but it may not.
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Offline ndcube

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Re: Correctly reading ph test strips
« Reply #12 on: January 13, 2010, 11:11:39 AM »
So the buffer 5.2 product should bring your pH to 5.5 at room temp...

It should, but it may not.

Right.  I guess I was just making a point to why it was called 5.2 and not 5.5.

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Re: Correctly reading ph test strips
« Reply #13 on: January 13, 2010, 11:12:06 AM »
It should, but it may not.

I would amend that to say "probably won't". Buffers, pretty much by definition, can only adjust the pH to a target if it's within a certain range to begin with. I used the 5.2 product for about half a dozen batches, then I bought some pH strips and discovered that it doesn't actually work very well - and I was already getting my water "close" and only using the buffer to dial it in.
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Offline Thirsty_Monk

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Re: Correctly reading ph test strips
« Reply #14 on: January 13, 2010, 08:07:03 PM »
I don't exactly know where this 5.2 mash pH target comes from. The literature I read indicates that 5.4-5.6 is a better target. Those numbers, however, are for room temp samples.

Kai

So if 5.4 - 5.6 is the target, and that's at room temperature, then the pH at mash temperature that's being targeted is 5.1 - 5.3.  Is that right?
If I get lucky my mash with colorpHast at room temp reads 5.3.
Normally it reads 5.0
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