Author Topic: Temperature and pH  (Read 10084 times)

Offline bluesman

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Re: Temperature and pH
« Reply #15 on: March 01, 2011, 10:54:43 AM »
I have has varying methods of cooling pH samples. My current method uses a 12ml glass vial on a stiff copper wire that I use to take a sample of mostly wort. Then I dip this in ice water and stir with the thermometer until the reading falls below 28 C. After that I immediately transfer this into a small medicine measuring cup where I then test its pH. Most of my recent pH experiments also used this method.
Kai

How much influence (if any) do you think evaporation plays on the actual measured value.

Assuming the sample is rapidly cooled...I would venture to say it is insignificant  :-\
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Offline Kaiser

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Re: Temperature and pH
« Reply #16 on: March 01, 2011, 11:09:52 AM »
How much influence (if any) do you think evaporation plays on the actual measured value.

Very little if any. The pH of the sample is determined by the pH buffers in it and the amount of water only plays a minor role.

Instead you need to be careful not to introduce any substances that can change pH.  In particular you should rinse any vessel with distilled or RO water instead of tap water. The smaller the sample the larger the impact of the alkalinity from the rinse water on the pH reading.

Kai

Offline Kaiser

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Re: Temperature and pH
« Reply #17 on: March 01, 2011, 11:17:28 AM »
And just so it's explicitly stated in this thread, room temp mash pH should be in what range?  5.2-5.6?

There doesn’t seem to be much agreement in the literature and authors don’t want to settle on a particular range.

Based on what I have read and what I do I think that 5.3-5.5 is the best range for mash pH. I may go higher (5.4-5.6) for decoction mashes and/or grists with lots of Munich malt.  But I welcome experimentation.

Kai

Offline Kit B

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Re: Temperature and pH
« Reply #18 on: March 01, 2011, 11:33:41 AM »
So, is this 0.35 variation a linear/across the board difference?
That is...
If I see that my pH needs some correction & is sitting at, say, 5.95 (measured at room temp.)...
Can I assume that the mash pH at 153* F is 5.6?

What if it's at 6.35, at room temp...Can I assume the same difference?
« Last Edit: March 01, 2011, 11:37:09 AM by Kit B »
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Offline tygo

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Re: Temperature and pH
« Reply #19 on: March 01, 2011, 11:34:32 AM »
Great info in this thread.  This confirms, more or less, that I've been going about it in the right way.  Although I guess I've been shooting for more in the 5.4 - 5.8 range and that may be a little on the high side but within the ballpark.
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Offline Kaiser

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Re: Temperature and pH
« Reply #20 on: March 01, 2011, 11:57:50 AM »
When looking for optimal mash pH you need to keep in mind that we are not just trying to make the amylase enzymes happy but we are trying to set the stage for the pH of other brewing processes. In particular boil and cast-out wort pH. This is why the cited range is a bit lower than what’s actually optimal for just amylase activity.

Kai

Offline Kaiser

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Re: Temperature and pH
« Reply #21 on: March 01, 2011, 11:59:17 AM »
So, is this 0.35 variation a linear/across the board difference?
 

I don’t know and I don’t think it matters much. If I were to take a guess, I would think that it is fairly linear in the pH range that interests us.

Kai

Offline mainebrewer

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Re: Temperature and pH
« Reply #22 on: March 02, 2011, 07:43:19 AM »
And just so it's explicitly stated in this thread, room temp mash pH should be in what range?  5.2-5.6?
Denny gets at my question a few post back.
What is the room temp mash pH target range?
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Offline mabrungard

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Re: Temperature and pH
« Reply #23 on: March 02, 2011, 12:19:15 PM »
All the data and texts I've seen indicate that the better pH range is 5.3 to 5.5.  I'm not sure there really is an optimum mash pH since a brewer can have differing goals for their brew.  These are room temp measurements.  Denny's range is a more forgiving 5.2 to 5.6, but it still centers on about 5.4 as the median value. 
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Offline mainebrewer

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Re: Temperature and pH
« Reply #24 on: March 03, 2011, 06:27:03 AM »
Martin, thanks!
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Offline gordonstrong

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Re: Temperature and pH
« Reply #25 on: March 03, 2011, 02:27:29 PM »
So, is this 0.35 variation a linear/across the board difference?

It's roughly linear, but it isn't a constant.  This difference is for mash temperatures.  It's larger at sparge temperatures (maybe 0.1 more).  The difference is 0 at room temp (68F, or whatever they were calibrated at).  And this is using water.  I've seen some (credible) sources say the variation is lower when using a mash rather than water (maybe 0.2).
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Offline Kaiser

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Re: Temperature and pH
« Reply #26 on: March 03, 2011, 02:56:33 PM »
So, is this 0.35 variation a linear/across the board difference?

It's roughly linear, but it isn't a constant.  This difference is for mash temperatures.  It's larger at sparge temperatures (maybe 0.1 more).  The difference is 0 at room temp (68F, or whatever they were calibrated at).  And this is using water.  I've seen some (credible) sources say the variation is lower when using a mash rather than water (maybe 0.2).

Gordon,

I’m very interested in the original source of this number. If it’s based on the pH change in plain water, which is caused by the change in the water’s dissociation constant, then the 0.35 number is not going to be correct in wort. This is because the pH of wort is determines by the dissociation constants of all the various acids that are in there.

Briggs, et. al. mentions a 0.35 shift at 65C and a 0.45 shift at 75 C.

Note that the 0.35 number may reflect both a change in mash pH as well as a shift in the enzyme’s pH optimum. Testing cold and hot wort with a temperature correcting pH meter only shows you the actual mash pH change.

BTW, congrats on your book that’s coming out soon.

Kai


Offline gordonstrong

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Re: Temperature and pH
« Reply #27 on: March 03, 2011, 03:53:17 PM »
I ran tests when working on my book.  I was doing a variety of tests to test pH adjustment and decided to capture the temperature curve while I was at it.  I did it in a chemistry lab with professional equipment (I have all the various models written down somewhere) and RO/distilled water.  Mostly I was trying to quantify the adjustment of sparge water.

The numbers you are quoting (0.35 @ 65C and 0.45 @ 75C) is what I was referring to when I said the variation at sparge temps were 0.1 higher than at mash temps.  So we're saying the same thing there.  A graph would illustrate it easier, but I didn't take the time to generate one.

I think it was private correspondence with A.J. deLange where he was telling me he thought 0.2 was more realistic in mash conditions than 0.35.  I just noted it, but didn't have a chance to test it.  I'm going based on memory, so it may be faulty.  I just found it interesting, and something I'd like to investigate myself some day.

Thanks about the book; I mention you (positively) in a few places.  
Gordon Strong • Beavercreek, Ohio • AHA Member since 1997 • Twitter: GordonStrong

Offline Kaiser

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Re: Temperature and pH
« Reply #28 on: March 03, 2011, 09:41:16 PM »
Gordon,

I did a similar experiment like yours with wort and found a pH shift of ~0.2. A.J. also mentioned to me that he found a similar number when he did such an experiment. But we both agree that the actual shift matters little if we stick to the convention of only testing and reporting room temp sample pH values.

Kai

Offline gordonstrong

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Re: Temperature and pH
« Reply #29 on: March 03, 2011, 09:46:47 PM »
OK, so now I heard it from two credible sources...
Gordon Strong • Beavercreek, Ohio • AHA Member since 1997 • Twitter: GordonStrong