Lactic acid in mash not affecting pH of my Belgian Wit? huh?

[kal]

This one's a head scratcher, but then I've never professed to be a chemistry expert:

I'm brewing a Belgian Wit today (recipe from Jamil's Brewing Classic Styles, online here) with the following grist:

46.2% Organic Pils (Weyermann)
42.1% Flaked Wheat [unmalted] (G&P)
9.5% Flaked Oat (G&P)
2.2% Munich II (9L)

Very light colour as expected (~2 SRM).

Using (very soft) Ottawa city water and just adding a touch of Gypsum, Calcium Chloride, and Epsom salt to hit certain minimum I wanted (Ca=50, Mg=10, Cl:SO4 ratio equal and low at 70:70).

Normally with so little salts added and a very light beer like this I end up having to add 1-2 ml of 88% lactic to the mash to get the pH down to around 5.2 (measured relative to mash temp) after mashing in. I add the grain & salts, stir well, and measure pH, then add some lactic about 1 ml at time. Normally with a ~10 gallon batch like this 1 ml takes my pH down 0.1.

However, this time it's just not working.

After adding as much as 6 ml the mash pH basically hasn't budged from 5.6 (relative to mash temp).

I measured pH at multiple times during the mash, including when I:

- Mashed in at 122F, held for 15 mins
- Rest at 154F for 60-90 mins (measured at the start and the end)

While a wit should be 'tart' I don't want to add any more lactic so I've stopped adding. Wort tastes sweet, and while pH is not in the 'ideal' range, conversion still seems to be happening well enough given some hydrometer measurements & conversion calcs I did. I should be reasonably on target of my pre-boil gravity.

I've brewed many wheat beers before that were 60% wheat malt and 40% pils (weizens) and adding lactic to the mash always brought the pH down as expected. This is the first time I've used this amount of flaked wheat and oat (adjuncts) however.

I confirmed that my pH meter's working correctly. Is there something about the low amount of 'regular' malt (pils & munich) doing this?

Any comments appreciated!

Kal

 

[kal]

To answer my own question: I would guess that the buffering of the flaked wheat was keeping the pH constant, 'overriding' the buffering of the wheat.

I knew that the unmalted wheat flakes needed to be mashed with the pils to get the enzymes needed, but didn't figure that there would be so much buffering ability. (?) I figured it would behave like most other standard base malts like 2-row, Pils or MO which I have no problems knocking down in pH with some lactic.

I could have kept adding lactic acid to break this but didn't feel it prudent. Not sure what others do about mash pH when brewing a wit like this. My searches for wit and mash pH are not coming up with anything useful.

For what it's worth, based on my preboil gravity, conversion happened exactly as expected...

Kal

 

[ajdelange]

The first thing I notice in your post is that you are specifying all the pH numbers to 1 decimal place. It is virtually impossible that you can be adding acid to a mixture of grains without the pH changing unless something is, as you have suggested, buffering strongly at the particular pH you would observe without the acid addition. But malts do not have the same sort of titration curve you would expect with a 'buffer' like the ones that you use to calibrate your meter. In a plot of mEq vs pH the strong buffer (like the calibration ones) show two flat portions (at below and above the pH of the buffer) connected by a pretty steep vertical portion. What this means is that you can add a lot of mEq and see only a small change in pH. The 'buffering capacity' of the buffer is high (high slope) of the titration curve. Malt curves are much gentler. The buffering capacity is there but the high slope (high buffering capacity) isn't.

It can take a long time for liquid acid which has been added to a mash to react. Even where the 'mash' is flour and the mix subject to constant stirring it can take more than an hour for equilibrium to be reached but even in those cases you should see a change much faster than that.

I'm going to boldly guess that you are using a pH meter with a precision of 0.1 because that enables me to offer a plausible explanation. Otherwise I am as mystified as you. Guessing that flaked unmalted wheat, on which I have no measurements, behaves much the same as flaked barley, on which I do, and assuming that you are mashing 30 lbs of grain with 10 gal water I'd estimate your mash pH, w/o lactic acid, to be 5.40 (referred to 50 °C). Adding 6 mL of lactic acid to that drops the estimated pH (again at 50 °C) to 5.27 or 0.13 pH. Allowing for errors in my assumptions about the amounts of grains you used and their buffering characteristics it is possible that the actual pH shift was less tha 0.1 and therefore not resolved by your meter.

As always, when pH readings are suspect, it is wise to do the pH meter stability and calibration checks suggested at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

 

[kal]

Thanks for the feedback. The pH meter I use is the Hanna Instruments HI98128:

ATC and has 2 digits after the decimal, but I was rounding here in my posts. pH may have been changing with the addtion of acid but it was a very small change, not what I'm used to seeing (hence the reason for my post).

As always, when pH readings are suspect, it is wise to do the pH meter stability and calibration checks suggested at https://www.homebrewtalk.com/f128/brew-science-forum-introduction-107178/

I don't see any checks suggested in that thread. Did you possibly mean this one?: https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

Thanks,

Kal

 

[ajdelange]

Ooops - grabbed the wrong link:

https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

You should be seeing a change of around 0.1 pH for that much acid addition (assuming the assumptions about volume and grain weight are approximately right). If not then the meter is the first target for suspicion.

The Hanna units are pretty stable but they suffer from taking the calibration measurements sooner than they should so they are often off by a bit. However they should be able to detect the change when acid is added.

Perhaps you should try a test mash in which you process about a pound of grist with a couple of quarts of warm water. You can, obviously, wait for hours to see where things settle out with a test mash without risking anything more than a pound of grain.

 

[kal]

Ooops - grabbed the wrong link:

https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

Thanks! I'll give it a read.

You should be seeing a change of around 0.1 pH for that much acid addition (assuming the assumptions about volume and grain weight are approximately right).

I would have expected even more actually (which is why I was confused).

This was 18.4 pounds of grain (making about 12 gallons of ~5 ABV beer). Normally when I mash in with this sort of light (2 SRM) beer with very limited salts added, I have to use lactic to bring the mash down to the right pH. Normally each 1 ml I add drops the mash pH by 0.1. I've made dozens of beers this way, but this is my first wit with more than 50% adjuncts. Hence my confusion when 6 ml later it had barely budged.

If not then the meter is the first target for suspicion.

I'll recalibrate, but in using 4 and 7 pH samples, it's working correctly.

However they should be able to detect the change when acid is added.

Exactly - I didn't want to side-track this into an accuracy question. Even if the meter's currently 'off', it should still move when acid is added (or so I thought).

Perhaps you should try a test mash in which you process about a pound of grist with a couple of quarts of warm water. You can, obviously, wait for hours to see where things settle out with a test mash without risking anything more than a pound of grain.

Good idea.

Thanks for the input!

Kal

 

[ajdelange]

I would have expected even more actually (which is why I was confused).

This was 18.4 pounds of grain (making about 12 gallons of ~5 ABV beer).
Normally when I mash in with this sort of light (2 SRM) beer with very limited salts added, I have to use lactic to bring the mash down to the right pH. Normally each 1 ml I add drops the mash pH by 0.1.

I've measured 5 base malts and found them to have an average buffering capacity of -41 mEq/kg. Flaked barley has buffering of -36 (all around the DI mash pH's). You have about 8.4 kg of grain and 1 mL of 88% lactic acid is going to give you about 12 mEq of protons to pH's around 5.3. Thus the expected shift would be about -12/(8.4*41)=0.035 pH if the malts were all base malts. This computation is pretty rough but you are seeing times 0.035 (i.e. 0.1) which means that your malts have buffering capacities about 1/3 what I (and Kai Troester) have measured. Something is weird here.

I've made dozens of beers this way, but this is my first wit with more than 50% adjuncts. Hence my confusion when 6 ml later it had barely budged.

AFAIK the adjuncts, since they have similar DI mash pH's and buffering capacities, should not change the picture much. The model I am using is not completely vetted so perhaps I should just say "I don't have an explanation."

 

[kal]

Well I'm not going nuts then! I expected the buffering ability of this grist to be similar to other light grain mashes I've done in the past...

More testing is required! Thanks for the input.

Kal

 

[kal]

Fast forward to today (10 days after brew day) and the beer's almost done fermenting and down to 1.012 (a point or so from FG). Tastes good too - slightly tart as expected.

Looks like conversion still happened. Was concerned that maybe I was reading soluble starch instead of sugar in the wort.

Brewing a repeat beer today (Irish Red Ale) and the pH meter and mash pH were exactly where I expected them to be.

Kal