Impact of Reiterated Mashing on mash pH

[bonecitybrewco]

Good afternoon,

Having a tough time finding any information on this so going to post it here considering the wealth of information available here and the wonderful people.

I am looking at doing a reiterated mash for my russian imperial stout, (mash half the grains, reheat and use the collected wort to mash the 2nd half of the grains) however am trying to calculate an accurate mash pH for the 2nd half of the grains. Does anyone have any thoughts or experience with this?

Thanks in advance.

 

[ancientmariner52]

Is this a thing? You may be the first to think of it.

 

[bonecitybrewco]

Is this a thing? You may be the first to think of it.

Yep, it's definitely a thing. I have found other people doing it, however, I am not finding anyone who seemed to be concerned about mash pH of the 2nd mash rest.

 

[ancientmariner52]

That's neat, I'll be following this with interest. Maybe do a micromash with a pound or so of grain and see what happens?

 

[bonecitybrewco]

That's neat, I'll be following this with interest. Maybe do a micromash with a pound or so of grain and see what happens?

This may very much turn into a trial and error thing... I am hoping Martin may be able to help.

 

[ajdelange]

Good afternoon,

Having a tough time finding any information on this so going to post it here considering the wealth of information available here and the wonderful people.

I am looking at doing a reiterated mash for my russian imperial stout, (mash half the grains, reheat and use the collected wort to mash the 2nd half of the grains) however am trying to calculate an accurate mash pH for the 2nd half of the grains. Does anyone have any thoughts or experience with this?

Thanks in advance.

Conceptually this is no more difficult than establishing pH for a normal mash. Problem is that few do this using the simple robust process that gives the best result but requires knowledge of malt properties. To estimate mash pH one picks a target pH close to the desired pH and then calculates the proton deficits and surfeits for each mash component at the chosen pH. This means the alkalinity of the water, any acid or base you have added and the deficit or surfeit for each malt. One then adjusts pH until the pH is found for which the sum of the deficits/surfeits is 0. Or one sets the desired pH and adjusts malts, acids and bases until a 0 sum is reached. This is easier and gets you right to your goal.

In the split case you would do the calculation with only the malts to be used in the initial mash. Be sure to adjust acid/base to get the desired pH for this first step.

Collect the first wort and measure its pH. Now calculate the deficit or surfeit of the second grain tranche at the pH you just measured. Add acid or base as required to get a 0 net deficit for this tranche. Add that acid or base to the second mash and you should be there.

 

[bonecitybrewco]

Thanks so much! It's actually rather simple when you lay it out like that. Interesting approach. Time to bust out the pad and paper!

 

[ajdelange]

It is indeed simple. The catch is that you have to have a model for the malts' proton deficits as a function of pH. This requires (for an accurate model) a tedious set of measurements on each malt. Fortunately, a fair approximation (probably at least as good as yoy can get from malt color models) can be had from the DI mash pH assuming the buffering is linear and the same for all malts And there is a small library of actual measured malt models which we can augment by drawing on Kai Troester's pioneering work. The model is

Proton_Deficit = -40*(pH - pHDI) mEq/kg

so that if you have a malt with pHDI = 5.65 and you want mash pH 5.45 the estimated deficit is approximately
-40*(5.45 - 5.65) = 8 mEq/kg

 

[chris000]

double mashing is cool. don't know why so few do it.
from what I understand the OP is only concerned about pH (not enzymes activity) and I assume is using the wort from the first mash for the second.
in case you are going to use the same malt(s) (i.e. ratio base to dark) in the first mash and the second, I doubt you would be all too far off.
in theory, yes you would need to adjust due to diff. conc., but mash pH is always a compromise and the second load shouldn't push you beyond the envelope.