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General Category => Ingredients => Topic started by: tygo on February 28, 2011, 01:51:08 AM

Title: Temperature and pH
Post by: tygo on February 28, 2011, 01:51:08 AM
I was going to add this as an aside to Kai's pH tool thread but figured it might be better as a separate topic.  I've looked around on the web before and haven't been able to find a good conversion for pH by temperature.  We say "mash temp" and "room temp" but is there a good reference for what that means and how temp affects pH?

I'm sure that for home brewing this is one of those topics where close enough is good enough but I was curious.
Title: Re: Temperature and pH
Post by: nateo on February 28, 2011, 03:32:54 AM
IIRC, pH at "mash temp" is about -0.3 lower than at "room temp." Mash temp is generally 149-160, I'd say. But I've checked pH at the protein rest step, which is 120-132*-ish and gotten closer values to "room temp" something more like -0.15. There is a relation between temp and pH, but I don't think it's linear.

Just checked myself, and to quote Kai (quoting Briggs):  "Briggs quotes a difference of 0.35 in pH between a mash pH measured at mash temps and the same liquid measured at room temp. The pH measured at mash temp is lower "
Title: Re: Temperature and pH
Post by: sharg54 on February 28, 2011, 05:45:28 AM
I don't know much about ph but I did run a short experament one time with my water to see what heat wouuld do to the ph levels and the hotter I got it the higher the ph would go and it only took a matter of seconds at boiling to blow it off the scale. In a mash however it acts totaly different depending on what malts you are using. With the use of say 10% crystal malts you can actually lower your ph by .03 to .05 depending on your grain bill and the use of acid malts can change it as well. I don't think there is actually a dependable standard chart you can get as there are to many varibles and the best thing you can do is monitor your ph with a good set of test strips and make adjustments as you go if need be. You can make a good base line from your water profile and grain bill but after that you need to teat and correct if need be on the fly.
Title: Re: Temperature and pH
Post by: mainebrewer on February 28, 2011, 12:52:14 PM
From what I've read, the target mash pH is around 5.3.
Is that a room temp or a mash temp measurement?
Title: Re: Temperature and pH
Post by: tygo on February 28, 2011, 01:01:42 PM
That's the mash temp pH target (or thereabouts).
Title: Re: Temperature and pH
Post by: mainebrewer on March 01, 2011, 01:58:46 PM
Thanks!
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 02:46:13 PM
This comes up once in a while and I just had an e-mail discussion with a fellow home brewer on the same subject.

Fact is that the pH of a solution changes with temperature. It is caused by a change of the dissociation constants of the various acids/bases that are in the solution. Even water is considered an acid since it can donate hydrogen ions although in most cases it is not dominating pH at all. The extent of the change depends on the substance. Even the pH optimum of enzymes may shift with temperature. I believe that the0.35 correction factor for mash temp (65 C) vs. room temp (25 C) pH contains both the aspect that the actual pH in the mash is lower at 65 C that it is at 25 C and that the pH optimum of the amylase enzymes shifts a bit from the value that can be observed by room temperature mashing.

But none of this matters since by convention pH values in brewing are reported as the pH of a room temperature sample. This arises from the laboratory practice of cooling pH samples before pH is tested. This also means that reported pH optima and pH ranges are for room temperature samples even though the actual reaction happens at higher temperatures. A.J. deLange mentioned to me the “by convention” aspect. Another thing we express “by convention” is SG. By convention we always correct SG for temperature since we all assume that the reported SG applies to a 68 F sample. The same is and should be done for pH measurements. To be exact you’ll have to cool hot samples and warm cold (e.g. beer) samples.

It’s also helpful to take into account how we arrived at these pH optima/ranges. They are determined by conducting a series of mashes (at correct mash temp for that enzyme) with differing pH. The pH is tested in a room temp sample. The amount of product produced during these reactions (sugar, for example) is then plotted over this room temperature pH.

The same is true with boil pH recommendations.

One problem is that hardly any author is explicit about this. I assume that most of them see it as a given that they talk about pH from room temperature samples. Briggs was the only one I found that made a distinction. This lack of explicitness, if this is a word, seems to cause a lot of confusion with home brewers.

Kai
Title: Re: Temperature and pH
Post by: johnf on March 01, 2011, 03:25:23 PM
That's the mash temp pH target (or thereabouts).

Optimal mash pH ranges are varying expressed as anywhere between 5.2 and 5.7, at room temperature. So 5.3 at either temperature would fall within that range.

The important point being that any professional or academic source quoting a pH or range would be talking about room temperature. Only homebrewers talk about pH at mash temperature because they mostly do not use pH meters and do not know that it is impractical to measure at mash temperature.
Title: Re: Temperature and pH
Post by: glastctbrew on March 01, 2011, 03:49:47 PM
Ok, just want to make sure I've got this straight since I'm an accountant and not a chemist.  If I use a ph meter with temperature compensation, it is giving me a reading  at "room temp" as long as my sample is within the temperature range the meter is rated for, right?  For example.  I have a Milwaukee ph56.  The effective temp range is 23 to 140 F (-5 to 60 C).  As long as I have my sample is cooled to at least 140F the reading I get will be as if the sample was at 68F.
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 03:55:47 PM
I think John Palmer started some of this confusion.

While he may have corrected this in subsequent editions the following is from the widely referenced on-line edition of How-To-Brew (http://www.howtobrew.com/section3/chapter15-2.html):

“When you mash 100% base malt grist with distilled water, you will usually get a mash pH between 5.7-5.8. (Remember, the target is 5.1-5.5 pH.)”

In this sentence he mixes room temp and mash temp pH values. The 5.7-5.8 base malt pH is correct when seen as the pH of a room temperature mash sample while the 5.1-5.5 pH target is only correct when seen as a mash temp pH target with a conversion factor of 0.35. With this the room temp sample pH target range is 5.45 – 5.85, which is more correct.

The pH optima that John cites for various enzymes seem to be mash temp pH values. He doesn’t quote a source but the only source that I found which lists mash temp pH values is Briggs’s Brewing Practice and Science book. In this he also gives room temp pH numbers.

Kai


Title: Re: Temperature and pH
Post by: johnf on March 01, 2011, 04:26:25 PM
Ok, just want to make sure I've got this straight since I'm an accountant and not a chemist.  If I use a ph meter with temperature compensation, it is giving me a reading  at "room temp" as long as my sample is within the temperature range the meter is rated for, right?  For example.  I have a Milwaukee ph56.  The effective temp range is 23 to 140 F (-5 to 60 C).  As long as I have my sample is cooled to at least 140F the reading I get will be as if the sample was at 68F.

A pH meter without ATC would read different at two different temperatures for two reasons.

1. The way the probe works is that temperature in and of itself affects the reading regardless of actual pH.
2. The actual pH is different at different temperatures.

The ATC attempts to correct for the first. I say attempts because the ATC assumes the probe is in perfect condition and the sub $100 probes most homebrewers use probably weren't all that perfect out of the box and certainly aren't after months of use. ATC does nothing to correct for the second. Even if your probe is perfect, if you read at 140 and then again at 75 you will get two different readings because of the second factor.

Furthermore if you measure at 140F you will place a great deal of stress on the probe and dramatically shorten its life. Very inexpensive probes are around $40 these days so my choice though I am not a very cheap homebrewer is to not going sticking them in hot stuff when I can just leave the sample in a small steel bowl in the freezer for a few minutes.

In terms of having consistent readings that you can compare from batch to batch, you should try to always measure at the same temperature. If you want readings that you can compare to literature or other brewers and you don't want to be buying probes every couple of months 25C is the best temperature to do the readings at.

My advice is measure at room temp and forget you ever heard about mash temp pH.
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 05:01:33 PM
My advice is measure at room temp and forget you ever heard about mash temp pH.

I can only agree with what John is saying and a pH meter being labeled as “ATC” may lure some into thinking that it corrects for that ominous 0.35 pH shift that is commonly cited.

I’m even going so far to say that there is no use for the ATC feature in brewing. pH samples should be measured at room temp (I chose 25C since this is the temp at which the calibration buffers are correct) and thus no ATC is needed.

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

Title: Re: Temperature and pH
Post by: glastctbrew on March 01, 2011, 05:17:30 PM
Huh?  ATC?  Never heard of it ;D

This sounds like good advice.  I'll come up with a consistent sampling method that will work in my environment and never look back.

Thanks for the feedback.
Title: Re: Temperature and pH
Post by: mabrungard on March 01, 2011, 05:36:59 PM
Yep, no ATC is the way to go.  There are too many variables and an ATC pH meter's abilities do not cover all the changes in mash pH that occur with temperature change.  All pH measurement must be performed at room temperature.
Title: Re: Temperature and pH
Post by: denny on March 01, 2011, 05:46:58 PM
And just so it's explicitly stated in this thread, room temp mash pH should be in what range?  5.2-5.6?
Title: Re: Temperature and pH
Post by: bluesman on March 01, 2011, 05:54:43 PM
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  :-\
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 06:09:52 PM
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
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 06:17:28 PM
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
Title: Re: Temperature and pH
Post by: Kit B on March 01, 2011, 06:33:41 PM
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?
Title: Re: Temperature and pH
Post by: tygo on March 01, 2011, 06:34:32 PM
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.
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 06:57:50 PM
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
Title: Re: Temperature and pH
Post by: Kaiser on March 01, 2011, 06:59:17 PM
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
Title: Re: Temperature and pH
Post by: mainebrewer on March 02, 2011, 02:43:19 PM
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?
Title: Re: Temperature and pH
Post by: mabrungard on March 02, 2011, 07:19:15 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. 
Title: Re: Temperature and pH
Post by: mainebrewer on March 03, 2011, 01:27:03 PM
Martin, thanks!
Title: Re: Temperature and pH
Post by: gordonstrong on March 03, 2011, 09:27:29 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).
Title: Re: Temperature and pH
Post by: Kaiser on March 03, 2011, 09:56:33 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

Title: Re: Temperature and pH
Post by: gordonstrong on March 03, 2011, 10:53:17 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.  
Title: Re: Temperature and pH
Post by: Kaiser on March 04, 2011, 04:41:16 AM
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
Title: Re: Temperature and pH
Post by: gordonstrong on March 04, 2011, 04:46:47 AM
OK, so now I heard it from two credible sources...