Author Topic: mash pH changes over time  (Read 1772 times)

Online Kaiser

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mash pH changes over time
« on: January 07, 2011, 10:50:37 PM »
Here is an interesting pH behavior that I observed today when I was testing the behavior of phosphoric acid additions:



These were 6 test mashes mashed at about 60C. various amounts of phosphoric acid were added 5 min after dough-in. Mash pH was tested 20 and 60 min after dough-in.

What is interesting is that during the mash the mash build up a stronger buffer. I.e. the amount of added acid had less on an effect on the mash pH after 60 min (~30 mEq were needed for each kg of malt and a drop of 1 pH unit) than it had at 20 min (only 15 mEq/(pH*kg) were needed. After doing the initial pH measurements I thought something was wrong with the amount of acidity I contribute to the phosphoric acid since I was expecting 30 mEq/(pH*kg) but then I had the 2nd pH tests and they made more sense.

I don't know if this is something that is unique to phosphoric acid. Previous experiments, that evaluated the effect acids and bases have on the mash, were not set up like this one. But the ones that tested pH at different times show the same trend. A mash buffer strength of ~30 mEq/(pH * kg) is what I was expecting from previous experiments. I'll have to pay attention to this effect in future mash experiments.

In practical brewing you may have seen that the initial test of the mash pH was much lower than expected while later tests would have shown an increased mash pH. In fact I have seen changed of mash pH during mashing w/o the addition of acids or salts. But the extend of the pH change was not always the same. It is very much possible that it takes some time for the pH active substances to be released during mashing, which is why I think getting your mash chemistry correct at dough-in and thus preventing the need for pH corrections, has its merit.

Kai

« Last Edit: January 07, 2011, 10:56:34 PM by Kaiser »

Offline mabrungard

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Re: mash pH changes over time
« Reply #1 on: January 08, 2011, 06:58:25 AM »
That is an interesting result. 

One thing I'm thinking is that maybe Palmer's contention that adding phosphoric acid to the mash causes Ca to complex and precipitate.  I don't believe in that theory since there is already a huge amount of phosphate compounds in the mash from the grain.  But, those are different ionic forms from that added by phosphoric acid. 

The other reason could be that the protonation of phosphoric acid takes time to activate.  But that theory immediately falls apart since the 60 min response shows that the acidity (slope of the line) of that addition is less than the 20 min.  So, pooh pooh on that idea.

Have you performed a similar study using another acid?  If that acid does not present this sort of response, then it could be an indicator that phosphoric acid does cause the Ca complexing and precipitation as Palmer contends.

I look forward to hearing more.
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Online Kaiser

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Re: mash pH changes over time
« Reply #2 on: January 08, 2011, 11:10:22 AM »
Have you performed a similar study using another acid?  If that acid does not present this sort of response, then it could be an indicator that phosphoric acid does cause the Ca complexing and precipitation as Palmer contends.


Not as directly as this experiment. I keep optimizing the way I test the effects of various mash additions to make the results more or less applicable to actual brewing practice. I'll have to give lactic acid a test as well. but before that I want to run the same experiment with my well water which has a more substantial amount of calcium than the reverse osmosis water I used.

Kai

Offline thcipriani

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Re: mash pH changes over time
« Reply #3 on: January 08, 2011, 04:18:21 PM »
I've been thinking about pH and temp optimums vs enzymes activity recently as I've been using a hochkurz mash on some lagers I've been doing.

I wonder if this observation has any effect on efficiency in hochkurz mash since the mash is first rest at a temperature that favors beta-amylase and then moved to a temperature that more-heavily favors alpha-amylase. Since your pH (assuming you adjust down to between 5.2 to 5.4 at the beginning of the mash) would naturally be moving to favor these respective enzymes' activity as you moved through the rests - assuming, of  course, that these observations hold in a more typical brewing environment. Also, I wonder if there would be any benefit (efficiency wise) to exacerbating this effect in a hochkurz mashing schema. Also, I wonder if I should start altering when I check my pH.
Tyler Cipriani
Longmont, CO

Online Kaiser

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Re: mash pH changes over time
« Reply #4 on: January 08, 2011, 10:25:23 PM »
Tyler,

Yes that pH change can also have an effect on the enzyme activity. But I don't know how quickly the pH change happened after the first pH test.

Looking back at my notes I only see one case where the pH after adding lactic acid was lower than what I expected. But later the pH of the first wort was as expected. I first contributed this to incorrect measurements but it could have been the effect I'm seeing here.

Kai

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Re: mash pH changes over time
« Reply #5 on: January 10, 2011, 07:48:49 AM »
I ran the same experiment again with my well water which has a residual alkalinity of 140 ppm as CaCO3 and a calcium content of 78 ppm.

The resulting curves have been added to the chart posted in the initial post. The 60 min test had the expected ~30 mEq/(pH*kg) slope. But the 20 min test showed one oddity. For the first 3 test points the slope is ~15 mEq(pH*kg) which matches the 20 min slope when R/O water was used in the mash. But then the slope flattened out to ~30 mEq/(pH*kg). I’m not sure to what extent this is the result of measurement inaccuracies, but it is entirely possible that this is an reaction between phosphate and calcium. Though it is odd that after 60 min none of that effect remains.

I really wonder how much more time I want to invest in this. The more I look into something the more questions I end up digging up. Using phosphoric acid in practical brewing and checking if it behaves as expected might be more appropriate at this point. For now I think it is safe to assume that phosphoric acid changes the mash pH like all the other acids I tested although there might be an initial drop. So I’ll just add it as another acid to my water spreadsheet.

BTW, Blatz recently contacted me and reported that my recommendation of blindly adding acid malt to his pilsner grist dropped the pH much more than expected. He ended up adding chalk to bring the pH back up. Now I wonder if he saw exactly this phenomenon and if his pH would have climbed back up on its own?

Obviously, if there  are significant pH changes over time during mashing, how much can we trust a pH reading that is taken after 5-10 min?

Kai



Offline tomsawyer

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Re: mash pH changes over time
« Reply #6 on: January 10, 2011, 09:08:28 AM »
I would suppose the generally accepted recommended pH ranges are taken early in the mash, so if there is drift upwards it really won't matter.  One might shoot for the lower end of the acceptable range, knowing it will drift up.  But the acceptable range is broad enough that it probably doesn't matter.  Since the pH is simply affecting the amylases' reaction rate, a few more minutes with a slightly lower rate accomplishes the same thing.  As long as you are allowing time enough for all the starch to be hydrolyzed to sugar, it won't much matter what the exact pH is.
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Offline tschmidlin

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Re: mash pH changes over time
« Reply #7 on: January 10, 2011, 11:04:22 AM »
I would suppose the generally accepted recommended pH ranges are taken early in the mash,
I could be wrong, but I think the pH recommendations are based on enzyme effectiveness at various pHs, not on measurements taken in mashes.
Tom Schmidlin

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Re: mash pH changes over time
« Reply #8 on: January 10, 2011, 11:42:59 AM »
Obviously, if there  are significant pH changes over time during mashing, how much can we trust a pH reading that is taken after 5-10 min?

Kai




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Online Kaiser

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Re: mash pH changes over time
« Reply #9 on: January 10, 2011, 12:49:03 PM »
I would suppose the generally accepted recommended pH ranges are taken early in the mash,
I could be wrong, but I think the pH recommendations are based on enzyme effectiveness at various pHs, not on measurements taken in mashes.

To my knowledge the pH optima for mashing are determined by running test mashes with differing pH values. The resulting worts are then analyzed and the results are plotted over pH. It is also possible to assess the pH sensitivity of individual enzymes in controlled substrate substances but it has been found for the amylases, for example, that the pH optima for mash and pure starch solutions are different.
So if there is a significant change of pH during mashing it would matter when the pH of the test mashes was tested.
Another factor, that likely affects pH stabilization, is the grist preparation. I would expect the pH in mashes with pulverized grists to settle faster than in mashes with typical milled grists. I have found some dependency between mill gap and mash pH, but didn’t evaluate mash pH change over time.

Kai

Offline estrauss

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Re: mash pH changes over time
« Reply #10 on: October 17, 2013, 09:48:35 AM »
Here is an interesting pH behavior that I observed today when I was testing the behavior of phosphoric acid additions:





This looks like an interesting topic, but the chart image is missing now.

Offline tcanova

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Re: mash pH changes over time
« Reply #11 on: October 17, 2013, 01:20:49 PM »
You can go to Kaiser's homepage and check it out.  Lots of info there.
http://braukaiser.com/wiki/index.php?title=Main_Page
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Offline estrauss

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Re: mash pH changes over time
« Reply #12 on: October 18, 2013, 04:44:54 AM »
You can go to Kaiser's homepage and check it out.  Lots of info there.
http://braukaiser.com/wiki/index.php?title=Main_Page

Yes, excellent site.  I've been there, I was just curious about this exact chart and experimentation.  Armed with a pH meter now and the GH/KH test kit, I'm learning more about water beyond just pH test strips.