Roast malt pH - Bru'n Water vs. BrewersFriend

[seven9st_surfer]

I really didn't want to start another BW vs BF thread, but I can't find my answer using search. With only base and crystal malts, the differences are within 0.05 of each other. My problem is whenever I start adding roasted malts to my grain bill, the two start giving me drastically different pH levels. Example using 7g distilled mash water and 1.5g sparge (BIAB with small sparge) and no salt or acid additions for both mashes:

BW:
9.5# Maris Otter
pH: 5.69

BF:
9.5# Maris Otter
pH: 5.65

Difference: 0.04

--------

BW:
9.5# Maris Otter
1# Crystal 120
pH: 5.51

BF:
9.5# Maris Otter
1# Crystal 120
pH: 5.49

Difference: 0.02

--------

BW:
9.5# Maris Otter
1# Crystal 120
1# Chocolate (225L)
pH: 5.27

BF:
9.5# Maris Otter
1# Crystal 120
1# Chocolate (225L)
pH: 5.39

Difference: 0.12

--------

BW:
9.5# Maris Otter
1# Crystal 120
1# Chocolate (225L)
0.5# Black Malt (500L)
pH: 5.14

BF:
9.5# Maris Otter
1# Crystal 120
1# Chocolate (225L)
0.5# Black malt (500L)
pH: 5.35

Difference: 0.21


The more roasted malt in the recipe, the wider the margin becomes, with BW estimating a much lower pH. I've double, triple, and quadruple checked with multiple recipes and made sure that all other variables are the same between the 2 programs. Has anyone else noticed this, or have an explanation? I've always used BF in the past, but started using BW more recently after reading how people tend to find it more accurate. Thanks for any help.

 

[Silver_Is_Money]

For grins, try Brewer's Friend while using these DI mash pH values:

Maris Otter: 5.51
120L Crystal: 4.58
225L Chocolate: 4.45
500L Black: 4.45 (same as above, not a typo)

 

[mabrungard]

DI pH values are not very useful with respect to the roast grains. The pH response can't be extrapolated into a mash pH contribution. The titratable acidity of those roast grains are more informative and useful.

The latest versions of Bru'n Water do include a higher acidity for roast grains. That is based on actual modeling and measurement for hundreds of mashes that include roast grains. The bottom line is that Bru'n Water predicts a lower wort pH when roast grains are in the grist.

 

[seven9st_surfer]

Awesome, thanks for the feedback, guys. I guess I'll go with BW and measure as I go. I don't trust my cheap pH meter any farther than I can throw it, but it's better than nothing.

 

[ajdelange]

DI pH values are not very useful with respect to the roast grains. The pH response can't be extrapolated into a mash pH contribution. The titratable acidity of those roast grains are more informative and useful.

The DI mash pH is indeed very important as it is an integral part of the titratable acidity specification. The titratable acidity of a malt between pHdi and pH (and please note that once cannot talk about titratable acidity or alkalinity without specifying the pH points between which he is specifying it) is:

mEq/kg = a*(pH - pHdi) + b*(pH - pHdi)^2 + b*(pH - pHdi)^3

where a, b, c and pHdi are 4 parameters which describe the particular malt and pH is the pH at which you want to know the acidity. pHdi is the most important of those parameters because if you know it you can get a pretty good estimate of the titratable acidity from mEq/kg = -45.7*(pH - pHdi) though, of course you, will get a better one if you know the actual value of a and better still if you also have the actual values for b and c.

It's clearly pretty simple to get pHdi. While you are at it take another measurement on a separate but otherwise identical test mash to which you have added a few mEq/kg strong alkali. The amount of base added divided by the change in pH is a. To get b and c you clearly have to make multiple measurements and use a curve fitting routine to get the ones that best fit the data.

There has been a fair amount of discussion of this fairly recently though it seems to have died down.

The number a = -45.7 is derived from measurements made by me and others on several malts (n = 39, average 45.7, sd = 14.3). If you are familiar with the ways of error analysis it won't take long to convince yourself that accurate knowledge of pHdi is so much more important than accurate knowledge of a (or the other parameters to the extent that we can set them both to 0).

In summary, pHdi is indeed very useful and one can calculate the contribution to mash pH of dark malts surprisingly well using it and - 45.7 as a WAG at the malts linear buffering term. Of course you may encounter a rogue malt that has a far removed from - 45.7 so it is always best to have at least the correct value for a (it only costs you one extra measurement) and preferrably b and c.

 

[Silver_Is_Money]

BW:
9.5# Maris Otter
1# Crystal 120
1# Chocolate (225L)
0.5# Black Malt (500L)
pH: 5.14

BF:
9.5# Maris Otter
1# Crystal 120
1# Chocolate (225L)
0.5# Black malt (500L)
pH: 5.35

Difference: 0.21

My initial projection for the above when mashed in 7 gallons of straight DI water is a pH of 5.30, but Martin assuredly knows a lot more about these things than I do. Will you be trying this and measuring the pH? I would presume that if you mash in DI, distilled, or RO, you will need to mineralize your sparge water, or add minerals during the boil.

AJ, would you care to calculate a 'projected' mash pH for this grist in 7 gallons of straight DI water.

 

[ajdelange]

I get 5.48 if I specify Crisp MO and 5.60 using Muntons.

The difference is obviously due to the base malts and in fact, mostly to their pHdi's being, respectively, 5.69 for the Crisp and 5.84 for the Muntons. Interestingly enough the shape of the titration curves are nearly identical as a, b and c are all very close. If I use 5.34 as suggested for MO's pHdi in #2 I get 5.30 - very close to what you got. So again it is clear that pHdi is the most important parameter.

 

[seven9st_surfer]

Thanks for all the great responses, guys, I appreciate it. Starting to get a little over my head, but I'm trying to learn.

 

[Silver_Is_Money]

Interesting discussion. Do the enzymes which convert malt starches into fermentable (as well as unfermentable) sugars require the presence of minerals during the mash? Or are minerals (particularly meaning here calcium ions) only required by yeast during fermentation?

 

[ajdelange]

Yes they do but Mother Nature wouldn't send her children out into the harsh, cold world unequipped and so the grains themselves carry enough metals for this function.

 

[Silver_Is_Money]

Yes they do but Mother Nature wouldn't send her children out into the harsh, cold world unequipped and so the grains themselves carry enough metals for this function.

Thanks AJ! So do minerals (again meaning here primarily only Ca++ ions) really only need to be added to the wort sometime prior to (or simultaneous with) pitching the yeast then?

 

[ajdelange]

Strictly speaking they don't need to be added at all as the malt contains enough minerals to make it possible to brew with DI water. Such beer is likely to be found insipid however as the minerals have other beneficial effects in the mash tun (clear runoff, protection of enzymes against heat, oxalate precipitation, mash pH reduction...)

 

[Silver_Is_Money]

So minerals are added mainly to induce (or modify) character. I'm truly learning something here. I had always believed that at the very least, the yeast required their addition. An adage that I had taken to heart was to never go below about 40-50 ppm Ca++ ions. That's apparently for taste, and not for yeast nutrient requirements.

 

[mabrungard]

40 to 50 ppm Ca is useful in most brewing water. 40 ppm Ca in the mash is what I find to be a minimum needed to remove most oxalate from the wort. Ale brewing benefits from at least 50 ppm Ca to aid in yeast floccing. But your brewing water doesn't have to have those suggested minimums. You can brew with less Ca, but the beer does tend to be underflavored or insipid. This is just like leaving salt out of cooking...its still food and its still edible, its just not as tasty.

 

[Silver_Is_Money]

Thanks Martin!

 

[tgmartin000]

Are you using the most recent version of BW? I think it is v2.18? I recently downloaded the new version, after previously using v2.16. I found, compared to my MW-102 pH meter, v2.16 was within 0.1 units of my actual mash pH - usually 0.1 below measured pH.

However, with the new version, it was predicting mash pH about 0.4 below previously measured values. For instance, it predicted a mash pH of about 4.8 for an American stout I had brewed before, at a predicted/measured pH of 5.3/5.4.

I went back to the old version and all has been well. Sounds like the problem isn't as pronounced with light beers.

 

[ajdelange]

It isn't. Their pHdi's and a's are grouped more tightly than those of the colored malts.