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Old 12-07-2013, 02:15 AM   #21
ajdelange
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Originally Posted by vinpaysdoc View Post
Mashing with 1.25 qt/lb (roughly 3.05 gal) is where I get the 4.9 pH associated with this grain bill. I'm using 3.5 L Maris Otter. The decreased water accounts for a good bit of the difference.
That's a clue. There is so little alkalinity that the volume of water shouldn't make much difference. The water's deficit is about 2 mEq/gal. That's compared to a deficit of 41 mEq for the base malt and surfeit of about equal magnitude for the colored malts. Taking out or adding a gallon of water should shift the pH by 0.01 pH.


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Old 12-07-2013, 03:54 PM   #22
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In looking at the numbers again I am beginning to think I may understand the low pH estimates here. When Kai did his pioneering measurements (upon which I think, but am not certain, Bru'n Water is based) he assumed that buffering is independent of pH. It isn't. Looking at the data set in his paper the average buffering of the whole set is -41 mEq/kg-pH and only one malt shows a buffering capacity over 50. For the malts I measured the buffering is a function of pH at at pH 5.4 is 48 for Pils, 81 for chocolate and 61 for caramel. In the better model the dark malts will be more powerful as acids than Kai's model suggests but, more significantly, the base malt is a more powerful base. Because of the greater pH difference between malt DI pH and dark malt DI pH the base malt dominates and the pH calculates higher.



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Old 12-07-2013, 09:44 PM   #23
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Bru'n Water only uses Kai's grain data to formulate a correlation to the equivalents of acidity created for various grains. The rest of the mash pH prediction is based on the empirical results of myself and a select group of brewers that I trust.

To give a data point with which to check other models; I brewed the Reaper's Mild recipe which is known on this forum. It turns out to be one of the most acidic grists I've ever encountered in brewing. You will notice that it has a lot of crystal malt.

75% Marris Otter 4L,
20% Crystal 60L, and
5% Pale Chocolate 265L.

The mash thickness was 1.4 qts/lb and Ca:16, Mg: 5, and HCO3: 16 ppm.

The observed mash pH was 5.00. Following that reading, lime was added to raise the mash to 59 ppm Ca and the pH to 5.27. The Bru'n Water prediction for the mash without the lime was 5.1 and 5.4 with the lime addition. If anything, Bru'n Water tends to point a brewer to using a little less alkalinity since I am a firm believer that a beer is more likely to be better at a slightly low mash pH than a slightly high pH.

A similar brew was repeated a few months later and the low pH was again duplicated and resolved with a lime addition. I'm hoping AJ's model also duplicates this prediction. I know that the Brewer's Friend model did not match this result and I concluded it was flawed. I'm not sure if Kai subsequently revised his model. If AJ's model does not predict this result, I'm afraid his model is also suspect. The good thing is that most brewing IS NOT performed with such extreme grists and most models tend to agree for more typical mashing conditions. It's the very low pH range where it seems some models may falter.

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Old 12-08-2013, 03:44 PM   #24
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The observed mash pH was 5.00.
I'm sure you saw what you saw but this stretches credibility a bit. It's asking 1/4 of the grist in transitioning 0.3 - 0.4 pH to pull 3 times as much mass 0.6 pH. I'm not saying it can't happen but it certainly is attention getting. Looking at the base malt I measured in detail you would need 251 mEq to move 7.5 kg of that malt (DI pH 5.62 - note that this is actually lower than what is often reported for MO and lower than many other lots of Weyermanns Pils I have worked with) to pH 5. That's equivalent to 2.6mL of 88% lactic acid (at 1.4 qts/lb we're talking 7.9 gal water here). Half a kg of the 600L malt I measured can only supply about 12 of those and 2.5 kg of the 80L caramel I measured can only supply 39. I have no reason to think there is anything unusual about these three malts as the data more or less agree with what Kai found for similar malts with the exception of the fact that they exhibit somewhat higher buffering capacities than his data because of the way he measured buffering. There is also some variation beacuse there is variation in malts. I already have observed that the Weyermanns Pils I measured is atypically low in DI mash pH.

It's interesting to see what sort of a malt might be needed to produce a mash pH of 5.0 at 20% presence with this base malt and 5% chocolate. As noted Kai's method underestimates buffering (the highest buffering he reports is -60 mEq/kg-pH) so I used -90 which is closer to what I observed. Note that acidity is the product of buffering and pH shift so the lower the DI pH and the higher the buffering (magnitude) the more acid the malt is. A malt that makes up 1/5 of the grist with (linear) buffering capacity of -90 mEq/kg-pH would need a DI mash pH of 3.67. The lowest DI pH measured by Kai was 4.48 so you'd need a malt appreciably more acidic that that. The only thing that comes close to meeting these numbers that I know of is Sauermalz (DI pH 3.44 according to Kai).



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Originally Posted by mabrungard View Post
A similar brew was repeated a few months later and the low pH was again duplicated and resolved with a lime addition. I'm hoping AJ's model also duplicates this prediction.
It does match (est 5.1) if I use caramel malt with DI pH of 4.08 and buffering of -90 mEq/pH but of course I have no idea what the numbers for any of the malts you actually used in these brews were. If I were to put together a mash in those proportions using malts for which I do have data I would get a more reasonable pH of around 5.31. If I put this data into Brewer's Friend it comes up with a prediction of 5.41 Note that his estimate for the buffering capacity is -34 whereas the more detailed model gives -56 and that he predicts DI mash pH for the base malt as 5.66 whereas the malt I measured had a DI mash pH of 5.62.


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I know that the Brewer's Friend model did not match this result and I concluded it was flawed.
It doesn't but I'm not sure that is the right conclusion.

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Originally Posted by mabrungard View Post
f AJ's model does not predict this result, I'm afraid his model is also suspect.
All models are suspect. That's why we work so hard to validate and refine them. The model I am using is certainly robust WRT to the underlying science (it uses the chemist's 'proton condition') but it is not robust in the sense that I don't have the data on any of the malts a particular brewer is actually using. And of course this is a new model (proton condition certainly isn't new but application of it to brewing is to me). Surely someone else must have thought of it before I did.


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Originally Posted by mabrungard View Post
The good thing is that most brewing IS NOT performed with such extreme grists and most models tend to agree for more typical mashing conditions. It's the very low pH range where it seems some models may falter.
There is no reason why they should. A purely empirical model may get a bit shaky in regions where the data is thin (e.g. low pH mashes) but if one has a robust model for an acidic malt there is no reason that the use of as much of it as desired can't be used to predict very (relatively) acid mash pH. Unless we are suggesting that activity is increasing faster than hydrogen ion concentration and I don't think we are anywhere near that even at low mash pH.

I forgot to mention the upward drift of mash pH over time. It takes time for water to penetrate the grist and time for the grist to release its solubles into the water. That's why, technically, we should always ask not only about the temperature at which mash pH was measured but when. The time drift is especially noticeable when one of the malts is acidic as is apparently the case here. I wonder if that might be responsible for the low measured pH.
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Old 12-13-2013, 09:57 PM   #25
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The obvious thing for me to do here is a test mash but the pump in my DI water machine was kaput and so couldn't until I put a replacement in today. As noted in my last post the predicted pH for the malts I have data on was 5.31. In the test mash I did I used those three malts in the 75/20/5% ratio but I had 2 mVal alkalinity and 2 mVa each Ca and Mg hardness as well. These raise (RA = 57) the estimated pH to 5.36. Effective water to grist ratio was 1.2 qts/lb. The pH of the test mash measured at 48 °C but corrected to room temperature were 5.46, 5.46 and 5.47 at, respectively, 20, 25 and 30 min and, when the mash was cooled to room temperature and measured at room temperature, 5.46. Hot measurements were made against a hot buffer calibration and room temperature measurements against a room temperature buffer calibration. So I'm low by 0.1 pH which I can't really explain except that it could be aging of the malts (the titrations were done about 9 months ago). I wish I had done this experiment back then. It was hard to measure oout the tiny amounts of salts necessary to to prepare 0.1 L of mash water but as noted above the difference between 57 RA and 0 RA is only 0.05 pH and I wasn't off by that much.Is 0.1 pH as close as we can hope to get in a pH prediction even with careful malt measurement? I fear that may be the case with things like ageing, lot to lot and maltings to maltings variations being the killer. Can't draw too many conclusions from a single experiment, though.

The burning question remains as to how Martin could see pH 4.9 for a similar mash? And more than once. He has to have had a base malt with much lower DI pH and much lower buffering capacity and dark malts with much lower DI pH and much, much higher buffering capacity or both.

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Old 12-15-2013, 04:52 AM   #26
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So I'm low by 0.1 pH which I can't really explain except that it could be aging of the malts...
Actually I can explain it and it isn't aging. It came to me this morning at 3:30AM when the dog decided he had to go out. The malt I used to make the test mash wasn't the malt I measured. I remembered that I had used the rest of the bag I tested in a brew and had opened a new sack with the unused portion being what was in the Vittles Vault from which I grabbed malt for the test mash. First thing this morning I checked the pH of a cold DI water mash with the new Hach meter: 5.92! I don't thing I've ever measured a malt's DI pH that high. Had to go off to a meeting and when I came back I did a hot water DI mash on that malt and got 5.91 (referred to room temp). I'm thinking I have two batches of Weyermann's Pils one that comes in at pH 5.62 and the other at 5.91 (both referred to room temperature). Indeed I do but the high pH one is the floor malted stuff. Not only does it have a much higher DI pH but it's buffering is about 70% of what the pneumatically malted Weyermann Pils shows. Put the right malt model into the spreadsheet and the prediction rises to 5.449. What I observed at mash temperature referred to room temperature yesterday was 5.457, 5.462 and 5.466 (the 3rd decimal place isn't real but I can calculate it and do so that I can see small differences in relative pH) at 20, 25 and 30 minutes respectively and a sample cooled to room temperature measured 5.46.

So the model is definitely vindicated though we can't draw global conclusions from this one test.
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Old 12-15-2013, 04:49 PM   #27
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I can't really explain except that it could be aging of the malts..
AJ, any thoughts on this process as malts are stored? I wonder if environmental moisture impacts DI pH over time with a given batch as well. Theory being that bacteria *might* increase population as grain hydrates in storage. I realize it may be minimal, and I am not suggesting grain that spoils from too much moisture. I routinely freeze bags of base malt to kill any weevils, and I am fairly sure that process introduces at least some amount of moisture in the process.

I am wondering to what extend, compounded through packaging, distribution, storage at LHBS, repackaging (possible grind) may have relative to a given DI pH... could it be accounted for, or would it require a specific test mash before each brew (in which case, I assume we would have a true full recipe, not just a single malt)?
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Old 12-15-2013, 07:48 PM   #28
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In this case, at least, it turned out not to be aging but misidentification. The caramel and chocolate were measured back in March, the floor Pils yesterday. So unless one of the colored malts drifted in one direction and the other in the opposite direction age was not a factor here. I really have no feel for how much aging, within reason, might change DI pH (or buffering) except for the gut feeling that properly stored (Vittles vault, sealed package under N2 etc) it probably isn't much. Now moisture pickup is a different matter. If I measure 50 mEq/kg-pH on a malt that is an 'as is' number. If the moisture content is 2% then the dry basis buffering is 49 mEq/kg-pH and if I try to use the number measured as is on 2% malt with malt with a moisture content of 5% obviously there will be error.

Clearly if one has to do the elaborate measurements required to characterize a malt before each brew there will be little value to this method. There will be value of we find that it is relatively robust WRT malt characteristics. It is encouraging that I only got 0.1 pH error by using a dramatically different base malt in the first estimate I posted for this mash. I hope we will find that if we have, for example, data for a representative 80L caramel malt that will be good enough to represent 80L caramel malt in general. If that does not turn out to be the case then a test mash with the actual grains to be brewed with will be necessary.



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