Chasing pH
 

I'm trying to get a handle on water adjustments and pH control when using RO water as a starting point. The RO water I used gave TDS = 1 with my meter, so it seems quite good. A recent batch of American Pale Ale mash had 12.6 lbs. grain and 16.1 qts water, for a ratio of 1.28 gts/lb. I adjusted the RO water with some gypsum, calcium chloride, and epsom salt to give a composition close to that of the "amber balanced" profile in Bru'n Water. However, I did not add any alkalinity (with bicarbonate or pickling lime). Based on what I've read in the Primer and my own (limited) all grain experience thus far, it seems that in most cases it is necessary to add acid to the mash to reach the desired pH. Given that, why would I want to add any alkalinity to the RO water?

Anyway, my initial mash pH reading after 10 minutes was 5.82. So I added 0.85 ml lactic acid, expecting the pH to drop by about 0.1 unit, based on prior experience. Surprisingly, the pH dropped to 4.82. So I then added 0.5 gram pickling lime, which brought the pH back up to 5.80. A 0.4 ml lactic addition brought it back down to 5.59.

With these wild pH gyrations, it seems like the mash is behaving as if it has very little buffer capacity. This leaves me wondering whether it is desirable to add alkalinity to the RO water to give a more controllable pH adjustment, even though the inital pH will be too high. The adjusted water I used had only 13 ppm alkalinity and -31 RA. There is no indication in the primer about the need for buffering the water or adding alkalinity when making adjustments -- my understanding is that the grain itself has phosphates or other salts which provide buffering. But why did my mash show such wide pH swings? This all leaves me a little confused about the best way to adjust RO water to get the mash pH close to the desired range.

Was your pH meter calibrated and accurate? Those wild swings just aren't really possible.

Yep. Calibrated with pH 4 and 7 buffers, the same day.

Did you mash in, and stir until your arm fell off, and then let it sit for a couple of minutes before checking pH? And then when adding the lactic acid, again stir until your arm fell off and then let it rest before checking pH?

I've noticed it takes a LOT of stirring and about 10 minutes for any readings to stabilize.

Well, I did wait 10 minutes before the initial pH reading, and about 5 minutes after the lactic acid addition. I stirred, but my arm was still pretty well attached! I stirred again before taking the sample for the pH reading. Maybe it wasn't enough. I was concerned with heat loss with excessive stirring and repeated opening of the tun. I would certainly like to hit the target pH with a single acid/base addition, at most, and avoid all this fiddling with it.

You wouldn't unless mash pH went too low which it is unlikely to do in pale and even some quite dark beers.

For RO water to which some calcium salts have been added that is suspiciously high. When confronted with a pH reading that is out of line like this you should immediately check the calibration i.e. put the meter into the buffer solutions. It should read the pH listed for the buffer on the side of the package at for the temperature at which the reading was made. Economy meters are often quite unstable and don't hold calibration for more than a few minutes. Even a high quality meter can be mis calibrated. if the meter doesn't pass the calibration check recalibrate it, measure the mash again and then check the calibration.

If previous experience has shown a pH drop of 0.1 for an addition of that amount of lactic acid then clearly adding that amount of lactic acid again should produce that drop again but it didn't - it produced a drop 10 times normal. Something is very wrong here and the prime suspect is the meter. I would suggest calibrating it and then leaving the electrode in 4 buffer while recording pH readings over the course of perhaps an hour.

I think the problem is that you were chasing erroneous readings, not that the mash pH was (initially) terribly out of whack. It is well to keep in mind, however, that after and acid or alkali addition pH will continue to change over an hour or more. I have seen pale beer pH initially read at as low as 5 in a mash with 2 - 3% sauermalz only to settle in at 5.5 or so after perhaps 20 minutes.

It does in fact have buffering capacity (20 - 45 mEq/pH-kg) but the reactions take time so that it seems at first that it has less than it does. Put an erratic meter into this picture and it is easy to see why you might come to this conclusion.

Alkalinity is equivalent to negative acidity. What I mean here is that alkalinity is the amount of acid which must be added to a sample to reduce its pH from pHa to pHb (with these pH values dependent on the application). If you add 1 mEq of alkalinity it will take one more mEq of acid to make the shift. You get the same effect by adding 1 mEq less acid.


I am not certain but as noted I suspect the meter because of the intially high mash pH because of the precipitous drop and because your wording implies that you have done similar things before without these difficulites. Do the stability check in the pH meter cal instructions in the sticky. The other potential problem is the timing one and a third is, of course, that you slipped with the acid and used more than you intended to somehow.

If your meter passes the stability check then the recommendation would be
1. Add the acid in smaller increments
2. Go slow.

I did in fact keep the meter in the pH 4 buffer solution in between readings (with a quick swish in RO water before taking the mash readings). I use the little sachet buffer packets, which were opened fresh that day. I also cooled the samples down to room temp in an ice water bath before taking readings. I am reasonably confident that my pH readings are correct, but can't entirely rule out a problem with the meter or some sort of sampling error.

What I gather from this discussion is that what I observed is clearly not right or expected, and my question about adding alkalinity to RO water has been answered.

I'm leaning toward inadequate stirring and not enough equilibration time as the most likely explanations.

This still leaves me with the somewhat uncomfortable scenario of a fairly long waiting time between measurements, plus the time to cool down the sample before taking a reading. With a single pH adjustment the 60 minute mash time may be significantly consumed before the correct pH reading is obtained. Then there is the issue of heat loss due to opening and stirring. How to deal with this? In my example, the mash was fully converted in 40 minutes by the iodine test, and I was still fiddling with the pH. It seems as if you pretty much need to know what pH adjustment will work ahead of time. I suppose this come from experience. I'm just trying to get to the point where I have some confidence in making adjustments.

That, in a nutshell, is pretty much the story.

You may find doing a test mash (mash 1 pound of grain with acid addition scaled to that amount) helpful in this regard).

We always talk of a desired mash pH as if it is a static thing. It really isn't. The object of pH control is really a trajectory of pH. You want something like 5.4 - 5.5. for the bulk of the mash duration but you know that you may start out at 5.1 or even 5.0 (if supplemental acids have been used), move up to 5.3- 5.4 in 15 minutes or so and then more or less settle in at around 5.45 - 5.5 after 20 minutes. You then expecto pH to keep decreasing in the hope that it will be 5.0 - 5.3 in the kettle and in the 4's once fermentation gets going.

The 5.82 mash pH was an impossibility in my experience. There is no way that that pH is possible with a water with little alkalinity and a mildly acidic amber grist. Even Kolbach's and AJ's data with regard to RA and pH suggest that the pH is not possible.

A bit of caution needs to be applied with respect to the Kolbach pH predictions in relation to RA. Those predictions are for knockout wort pH which is several tenths above the initial wort pH. Those predictions are valid, unfortunately they are not useful in practice. An initial wort pH prediction is much more valuable to a brewer in practice. Bru'n Water provides an initial wort pH prediction. That is probably the reason that AJ disputed the results of Bru'n Water a while ago. He expected a prediction of 5.75 if you input a mash of distilled water and Pils malt. Since a brewer needs to have a prediction that is valid in the early part of the mash when they can actually do something about it, the early mash pH prediction is more useful. I never understood why there was such a discrepancy between my set of mash pH observations and AJ's and Kolbach's until today. As AJ mentions above, knockout pH is several tenths higher than the initial mash pH. With the latest pH model in Bru'n Water (available in the next release), the initial pH is about 5.55 with a distilled water and Pils mash. I believe that about two tenths difference is probably a valid offset between initial and knockout mash pH. So I'm more satisfied with the Bru'n Water pH predictions now.

OK, back to the OP's malady. With the hardening he did to the RO water and having an amber grist, I would expect that the initial mash pH would be in the 5.2 range since there was insufficient alkalinity in the mash water. Adding that dose of lactic acid would likely drop the mash pH to the 4.5 range (I assume 88% lactic). Clearly, there is something wrong with the pH meter reading in this case. The 0.5 gram addition of lime should only consume half the acid contributed by the original lactic dose. So for the pH to return to near its original value after that lime dose is impossible. The OP has a bad meter that apparently cannot be relied on.

To answer the OP's question on the need for alkalinity, only add the alkalinity needed by the mash and no more. Bru'n Water provides the tool for predicting what that level of alkalinity might be. If you want an even higher level of confidence in mash requirements, you could perform the mini mash AJ mentions. I fully expect that you did need the alkalinity in that amber mash and chasing the mash pH was an unfortunate result of a bad instrument.

Now you've got me worried about the meter, even though I was quite careful with the calibration and re-confirmed with pH 4 and 7 buffers after the mash was done. Does it matter whether there are bits of grain in the sample being measured, or is it necessary to strain it before taking a measurement? I still think inadequate stirring may have been part of my problem.

There is still something I'm unclear about:

This statement seems to be at odds with the primer. For a "baseline" beer, which my APA would conform to, the primer says to add a tsp of CaCl2 to 5 gallons of RO water, and to add some sauermalz (or lactic acid). This implies that without any added alkalinity in the water the pH of this grist would be high. Bru'n Water, on the other hand, predicts a pH of 5.2, indicating that alkalinity, rather than acid, is needed to get to the correct pH. This seems a rather fundamental difference, i.e., whether one would normally expect to need to adjust the pH up or down when using a simple amber mash with RO water.