Adjusting Mash PH post dough-in.

[Colbizle]

I was doughing in my cali common last night and I took a reading around 10 minutes in which was 5.24. I wanted to bring it up to 5.3~, but then I realized I didn't know how much to add to bring it from 5.24 to 5.3. So quickly in Bru'un water I just went back into the Water Adjustment tab and moved the pickling lime (Ca(OH)2) value until I saw a change in the Mash Acidification tab. I then subtracted the value of what I already added into the mash from my new value, measured that out on the scale, and then I was able to hit my target of 5.35 in the mash ph. (phew!)

So my question is, how the heck do I calculate my needed additions after I have already dough-in and undershoot or overshoot my target Mash PH. I felt like what I did above was pretty "hacky". I was using 10% phosopric acid to lower the PH and Pickling lime to raise it if need be.

I searched the threads and couldn't find this Q/A.

Cheers.

 

[Malt]

What you did was perfectly reasonable and acceptable. No reason to label it a hack.

 

[Colbizle]

What you did was perfectly reasonable and acceptable. No reason to label it a hack.

Fair enough :cross: I guess, I was just wondering if there exists a Mash PH adjustment calculator (for post dough-in) for scenarios such as this so I could make a more accurate adjustment.

 

[Malt]

The adjustment you made is about as accurate as it gets, unless you do a test mash.

You could add acid or alkalinity in very small quantities, stir, test, repeat... though that's subject to it's own set of quandary.

I don't believe a scale or nomograph could be constructed to accurately account for adjustments, though if you're familiar with water calculations and know the DI pH of your malts you might be able to hazard a guess on the fly.

 

[Colbizle]

The adjustment you made is about as accurate as it gets, unless you do a test mash.

You could add acid or alkalinity in very small quantities, stir, test, repeat... though that's subject to it's own set of quandary.

I don't believe a scale or nomograph could be constructed to accurately account for adjustments, though if you're familiar with water calculations and know the DI pH of your malts you might be able to hazard a guess on the fly.

Makes sense. Bru'un water is pretty damn accurate given if you calculate everything correctly so I'm ok with that.

I suppose now I can make those adjustments before hand in my notes so I don't run into the same issue when I make this recipe again. I see now that if you brew the same recipe multiple times, your water additions and mash ph should be pretty inline with subsequent mashes.

Thanks!

 

[mabrungard]

I have to caution brewers on prematurely adjusting mash pH. My last brew produced exactly the same response as the OP's, the early pH measurement was over a tenth lower than what I had targeted. But instead of worrying too much about it, I let the mash ride in the interest of science. I kept measuring pH for another half hour and watched the pH reading creep up to almost exactly the target value. I wish I could explain what transpired, but I can't. All I can say is that don't rely too much on an early pH reading. It could correct itself.

Another important consideration is that a slightly low mash and wort pH is not a terrible thing. Conversely, an overly high pH would be. So if your initial reading is a little low, wait another ten minutes and see if its starting to correct itself.

 

[Colbizle]

I have to caution brewers on prematurely adjusting mash pH. My last brew produced exactly the same response as the OP's, the early pH measurement was over a tenth lower than what I had targeted. But instead of worrying too much about it, I let the mash ride in the interest of science. I kept measuring pH for another half hour and watched the pH reading creep up to almost exactly the target value. I wish I could explain what transpired, but I can't. All I can say is that don't rely too much on an early pH reading. It could correct itself.

Another important consideration is that a slightly low mash and wort pH is not a terrible thing. Conversely, an overly high pH would be. So if your initial reading is a little low, wait another ten minutes and see if its starting to correct itself.

Great food for thought Martin. I was under the impression that you would want to get your Mash PH dialed in before starch conversion (alpha amylase) is over which can occur in less then 30 minutes. What is your opinion on that?

 

[cantrell00]

I have to caution brewers on prematurely adjusting mash pH. My last brew produced exactly the same response as the OP's, the early pH measurement was over a tenth lower than what I had targeted. But instead of worrying too much about it, I let the mash ride in the interest of science. I kept measuring pH for another half hour and watched the pH reading creep up to almost exactly the target value. I wish I could explain what transpired, but I can't. All I can say is that don't rely too much on an early pH reading. It could correct itself.

Another important consideration is that a slightly low mash and wort pH is not a terrible thing. Conversely, an overly high pH would be. So if your initial reading is a little low, wait another ten minutes and see if its starting to correct itself.

This has been my experience as well. I typically don't measure until 30 minutes into the mash... I wouldn't attempt to manipulate anything at that point either.. Just let it ride..

One question for you though... Do you see any reason why a mash (HERMS) recirculation could possibly alter the mash pH results? vs a static rest?

 

[Yooper]

While I agree that 5.24 is fine vs 5.3, I do have a chart on my brewery wall from the bottom of this page (scroll down!): http://braukaiser.com/wiki/index.php?title=Mash_pH_control

It has the amount of acid needed to drop the pH .1 for the common acids and the amount of common items for raising the alkalinity as well.

 

[Colbizle]

While I agree that 5.24 is fine vs 5.3, I do have a chart on my brewery wall from the bottom of this page (scroll down!): http://braukaiser.com/wiki/index.php?title=Mash_pH_control

It has the amount of acid needed to drop the pH .1 for the common acids and the amount of common items for raising the alkalinity as well.

This is a great reference point thanks yoop!

 

[ajdelange]

It is quite possible to calculate the amount of acid or base required for a given adjustment but I echo the comments of others that
1)It takes time for added acids and bases to reach the interior of the grain particles and react so that pH equilibrium is not reached for 20 - 30 minutes (or more) so that waiting to be sure where you are is a good idea.
2)In support of 1), a test mash is the prudent way to go.

In order to compute the required acid addition one needs to know the 'buffering capacity' of the mash. This is nothing more than the number of mEq of protons that are necessary to produce a unit pH change. For example a dry stout mash made with 62.5% Muntons Maris Otter, 25 % Flaked Barley and 12.5% Roast Barley totalling 6.4 kg would have a buffering capacity of -331 mEq/kg-pH at pH 5.60. To shift the pH of this mash down by 0.1 would, thus, require 33.1 mEq of acid.

There are, of course, a couple of catches here:
1)The buffering capacity depends on the pH. At pH 5.7 this example mash has a buffering capactity of -324 mEq/kg pH. That's not much of a change and the error induced because if it is certainly manageable.
2)To calculate the buffering for the mash you have to know what the buffering capacity of each malt and the alkalinity of any bicarbonate (alkalinity) in the mash water is. The buffering of the bicarbonate is easily calculated. The buffering of the malts involves a set of painstaking measurements for each of the malts you intend to use.

WRT 2) it is easier (much easier) to do a test mash than the measurements on each of the malts. Nonetheless a pretty diverse set of approximate (non linearity not accounted for) measurements were made by Kai Troester and I have done the detailed measurements on a handfull of malts. These suggest that the average buffering of malts might be -40 mEq/kg-pH. If we used that number with the example 6.4 kg mash for a 0.1 pH shift we'd get 0.1*64*40 = 25.6 mEq whereas the previous, more precise calculation indicated we'd need 33.1 mEq. That's really not that much of an error in the great scheme of things. Instead of getting the desired 0.1 pH depression we'd expect to get 0.1*25.6/33.1 = 0.077.

Clearly it is indeed possible to prepare a spreadsheet or calculator to do this kind of calculation or I wouldn't be able to throw out these numbers. I don't publicize that I have such a calculator because it requires users to employ the Excel Solver which seems to terrify most people and because without good malt models to put in the results are questionable. I don't have much malt data but do fairly well using Kai's linear approximations where I lack full measurements.

 

[Colbizle]

It is quite possible to calculate the amount of acid or base required for a given adjustment but I echo the comments of others that
1)It takes time for added acids and bases to reach the interior of the grain particles and react so that pH equilibrium is not reached for 20 - 30 minutes (or more) so that waiting to be sure where you are is a good idea.
2)In support of 1), a test mash is the prudent way to go.

In order to compute the required acid addition one needs to know the 'buffering capacity' of the mash. This is nothing more than the number of mEq of protons that are necessary to produce a unit pH change. For example a dry stout mash made with 62.5% Muntons Maris Otter, 25 % Flaked Barley and 12.5% Roast Barley totalling 6.4 kg would have a buffering capacity of -331 mEq/kg-pH at pH 5.60. To shift the pH of this mash down by 0.1 would, thus, require 33.1 mEq of acid.

There are, of course, a couple of catches here:
1)The buffering capacity depends on the pH. At pH 5.7 this example mash has a buffering capactity of -324 mEq/kg pH. That's not much of a change and the error induced because if it is certainly manageable.
2)To calculate the buffering for the mash you have to know what the buffering capacity of each malt and the alkalinity of any bicarbonate (alkalinity) in the mash water is. The buffering of the bicarbonate is easily calculated. The buffering of the malts involves a set of painstaking measurements for each of the malts you intend to use.

WRT 2) it is easier (much easier) to do a test mash than the measurements on each of the malts. Nonetheless a pretty diverse set of approximate (non linearity not accounted for) measurements were made by Kai Troester and I have done the detailed measurements on a handfull of malts. These suggest that the average buffering of malts might be -40 mEq/kg-pH. If we used that number with the example 6.4 kg mash for a 0.1 pH shift we'd get 0/64*40 = 25.6 mEq whereas the previous, more precise calculation indicated we'd need 33.1 mEq. That's really not that much of an error in the great scheme of things. Instead of getting the desired 0.1 pH depression we'd expect to get 0.1*25.6/33.1 = 0.077.

Clearly it is indeed possible to prepare a spreadsheet or calculator to do this kind of calculation or I wouldn't be able to throw out these numbers. I don't publicize that I have such a calculator because it requires users to employ the Excel Solver which seems to terrify most people and becuase without good malt models to put in the results are questionable. I don't have much malt data but do fairly well using Kai's linear approximations where I lack full measurements.

Thanks aj, I apperciate your insight on this.

 

[mabrungard]

There are two ways to mix: move the media or move the liquid. Matt Crispin proved that its very difficult to produce a homogenous mixture by moving the media (aka: stirring). But I have found that recirculating wort in a properly designed mash tun produces a very homogenous mixture in as little as 10 minutes (depends on the flow rate).

That is the great benefit of RIMS and HERMS since they both recirculate wort and produce homogenous conditions in the tun. That applies to both the chemistry and the heating. To me, its a no-brainer.

So the problem with static mashes is that it is a little harder to distribute mineral or acid additions through the mash evenly. This compounded if you add minerals or acids AFTER you have doughed in. This is the main reason why I recommend that brewers add all their mineral and acid additions to the water before adding the grain. With a little mixing in the HLT, you can assure that all the additions are fully dissolved and fully distributed in the water. When you add the grains, you can be assured that those additions are evenly distributed at that point.

 

[ajdelange]

There is no question that thorough mixing is required to get to equilibrium as quickly as possible. Brewers who use decoction mashing will have a pretty good idea of how long it takes to get a good mix as the returned decoction is darker than the rest mash. When the rest mash plus returned decoction is a uniform color, they are well mixed.

But mixing isn't the whole story. These reactions just take time. When I do measurements on the malts I pulverize in a spice grinder. The result is flour. This gets mixed with warm DI water and the amount of sulfuric acid or sodium hydroxide I am testing with. The mixture is stirred continuously for the first 10 minutes or so and frequently thereafter. The pH continues to change, rapidly at first but then more slowly for at least half an hour. At the end of half an hour any additional change is small.

I have also made pure calcium chloride from chalk by suspending the chalk in DI water and adding hydrochloric acid. At first there is, of course, lots of fizzing but after a bit of that one winds up with a milky suspension at pH 4 or so. That suspension contains fine particles of CaCO3 and an excess of HCl. It's pH rises over time as the particles react. Eventually one has a clear appearing solution with increasing pH IOW even when the particles are so small that the solution appears clear the reaction takes measurable time.