Mash pH and water numbers don't stack up

[Simonh82]

I finally picked up a decent pH meter, having used the nearly useless pH test strips so far. I brewed my first beer with its assistance last night and despite careful planning my mash pH was way out and I can't make the numbers add up. I wonder if anyone can help me understand what is going on.

The beer was a session rye IPA. I use a BIAB system with 24L of mash water. The malt bill was 2.9kg Maris Otter, 700g of rye malt, 100g Crystal 45L, 50g Special B 200L, 70g, Crystal 15L.

My water had alkalinityof 241ppm as CaCO3, (3.95 meq/L). Using Bru N' Water to target a mash pH of 5.46 I added 0.6g/L 14.4g total of Gypsum and 2.5ml/L 6ml total of 80% lactic acid. As the pH test strips I'd used previously had always suggested a low mash pH i only added 5.25ml of lactic acid initially.

When I took the reading for the mash pH 15 minutes in it was at 5.8. I quickly added about 2ml of lactic acid and this brought it down to 5.72. I then added 1.25ml of phosphoric acid and this brought it down to 5.58.

I don't know why the mash pH stayed so stubbornly high. The only thing I've done differently this time, apart from using the pH meter is that i usually use only phosphoric acid. Does lactic acid degrade over time? I've had the bottle for about 6 months unused.

As an aside I also tested my sparge water. To the 11L of water I had added 6.6g of Gypsum and 2.6ml of lactic acid. This should have got it to 5.5pH but when I tested it was at 6.6,down from 7.6 straight out of the tap. I really don't understand what is going on here.

Any thoughts would be gratefully received.

 

[mabrungard]

I haven't found that lactic acid degrades with time. How sure are you of the tap water alkalinity? It sounds as if the tap water alkalinity is higher than your report indicates.

 

[ajdelange]

I finally picked up a decent pH meter, having used the nearly useless pH test strips so far. I brewed my first beer with its assistance last night and despite careful planning my mash pH was way out and I can't make the numbers add up. I wonder if anyone can help me understand what is going on.

I'll start by noting that if you are new to pH measurement you are going to have erratic readings you can't explain. This is just the way it is with a new instrument. It doesn't do what you want it to until you learn how to play it.

Second, I don't know anything about this meter. There are some good meters in this price range and some that aren't. Most important for accurate readings is electrode stability. There are instructions at https://www.homebrewtalk.com/showthread.php?t=302256 on how to check this and it is important that you do so.

The beer was a session rye IPA. I use a BIAB system with 24L of mash water. The malt bill was 2.9kg Maris Otter, 700g of rye malt, 100g Crystal 45L, 50g Special B 200L, 70g, Crystal 15L.

OK

My water had alkalinityof 241ppm as CaCO3, (3.95 meq/L).

Alkalinity of 241 ppm as CaCO3 corresponds to 4.82 mEq/L. Bru'n water unfortunately asks for alkalinity in terms of bicarbonate which has confused more people than just you. I am assuming your water report says 3.95 mEq/L. This amounts to 197.5 ppm as CaCO3.

Using Bru N' Water to target a mash pH of 5.46 I added 0.6g/L 14.4g total of Gypsum and 2.5ml/L 6ml total of 80% lactic acid. As the pH test strips I'd used previously had always suggested a low mash pH i only added 5.25ml of lactic acid initially.

With 3.95 mEq/L and 24L of water you have a total water alkalinity of 94.8 mEq and will need, in order to get the water to a pH of 5.45, 85.6 mEq of acid to do that. 5.35 mL of 80% lactic is only going to give you 55 mEq so you are shy in acid on the water alone unless the specialty malts (and rye) provide some of this acid.

When I took the reading for the mash pH 15 minutes in it was at 5.8.

I have no data for rye. Modeling it as being fairly acidic (DI pH of 5.38, buffering -30 mEq/kg•pH, I calculate 5.74 as the pH using Munton's Maris Otter which is quite alkaline but 5.61 if I use Crisp MO.

I quickly added about 2ml of lactic acid and this brought it down to 5.72.

That computes to 5.63 for a Munton's like base malt and 5.50 for one more like Crisp.

I then added 1.25ml of phosphoric acid and this brought it down to 5.58.

You don't say what strength but were it 80% we would expect about 5.53 for Muntons and 5.40 for Crisp.

I don't know why the mash pH stayed so stubbornly high. The only thing I've done differently this time, apart from using the pH meter is that i usually use only phosphoric acid.

As you can see from the calculations given here it is entirely possible that your observations are entirely possible depending on the properties of the malts which, as the discussion shows, can be, with respect to the base malts which determine most of the grist's proton deficit, quite variable.

Does lactic acid degrade over time? I've had the bottle for about 6 months unused.

Yes it does but not over 6 months.

As an aside I also tested my sparge water. To the 11L of water I had added 6.6g of Gypsum and 2.6ml of lactic acid. This should have got it to 5.5pH

Assuming the alkalinity is really 3.95 then 2.6 mL should take 11 L of water at 7.6 down to pH 5.97.

...but when I tested it was at 6.6,down from 7.6 straight out of the tap. I really don't understand what is going on here.

But this isn't right either. For it to only go down to 6.6 implies an alkalinity of 8.7 mEq/L and that isn't reasonable.

I'll note that all the lactic acid sold on this side of the pond is 88% but you have stated 80% and I used that in all calculations.

I guess the bottom line here would be that you can't really rely on software unless you have solid data on the malts you are using (and a robust software to put that data into). It is generally best to use software only for ROM planning and then verify with test mashes. This is because of the variations in malt parameters. Add to that the probability of erroneous pH readings from inexperience in taking pH readings (eliminate that one if you are an experienced pH meter user from another context), the possibility of instability from an unverified meter and some lack of certainty in the water alkalinity. One or more of these factors may have contributed to your observations. Keep at it and I promise things will stabilize.

 

[Simonh82]

I haven't found that lactic acid degrades with time. How sure are you of the tap water alkalinity? It sounds as if the tap water alkalinity is higher than your report indicates.

I didn't check the alkalinity before hand as it had been stable for the last three times I'd checked it. I did check it afterwards and this gave a reading of 3.95 meq/L. I was lat back from work and brewing in the evening so just wanted to get on with it.

The original figures I was working with was an alkalinity of 216ppm, this should have given a mash pH of 5.38.

 

[Simonh82]

@ajdelange Thanks for the information about pH meter calibration and the detailed run through of the different variables. I did quite a bit of research before buying the pH meter. It received good reviews from people who seemed to know what they were doing and were using it for field science, not just pot heads testing their hydroponic set ups.

You are right that the alkalinity is 197.5 ppm, I got confused by the bicarbonate figure. This was based on a fish tank alkalinity test I carried out after the event. I have a detailed water report that put my alkalinity at 190ppm and the preceding tests that I had done with the fish tank kit had suggested an alkalinity of 216ppm, so that was what I was using at the time in Bru N' Water.

I just included the rye malt as a base malt. It was sold as having an ECB of 5 which equates to Lovibond of 2.4. The Marris Otter is 7 ECB (3L).

The Lactic acid is 80%, the phosphoric is 75%. The Gypsum also contributes quite a bit to the acidification. If I remove it from the calculations it raises the pH by 0.34.

I've had a bit of a break from brewing recently but I've got a few brews planned so hopefully I can dial things in soon.

 

[ajdelange]

@ajdelange Thanks for the information about pH meter calibration and the detailed run through of the different variables. I did quite a bit of research before buying the pH meter. It received good reviews from people who seemed to know what they were doing and were using it for field science, not just pot heads testing their hydroponic set ups.

It may be a perfectly fine meter but you need to check that. I have never seen discussed in a review (or anywhere) what 'accuracy' means in a pH meter. It means that when you finish the calibration that if you put the electrode back into the buffer it continues to read the buffer pH for some practical length of time. If the buffer pH is 4.01 at a given temperature and the meter continues to read 4.01 or within ±0.01 or 0.02 of that for several hours after that then you have a stable (and thus, accurate) electrode. If it wanders off to 4.08 in 15 minutes it isn't. Part of insuring stability is witholding acceptance of the calibration reading until it is definitely stabilized. Meters that automatically decide when to accept a buffer reading often accept it too soon. The meter may be inherently stable but doesn't appear to be so because the calibration parameters are deduced from a reading that was not at equilibrium. Such a meter is still usable as you can add or subtract a correction from the readings but it is best if the meter lets you decide when to accept a cal reading.

I just included the rye malt as a base malt.

You don't have much choice other than to do that but which base malt? As I discussed last time two maltsters' versions of Maris Otter pale ale malt with nearly the same color have quite different properties. I also mentioned that I have never measured rye nor have any of my correspondents so I do effectively the same thing: pick a malt that I have data for which I think might behave like rye. In either case it's a WAG. Is rye acidic (I'm guessing it is) or unusually alkaline (like wheat)?

It was sold as having an ECB of 5 which equates to Lovibond of 2.4. The Marris Otter is 7 ECB (3L).

Color is not a very good correlate of malt acidity or buffering but is really all you can do unless you want to measure the malt properties yourself. This is a time consuming process and there is no popular software which can use the data. The point being, again, that you really can't rely on software to do much more than give you an idea as to what might happen. The discrepancy you have seen between prediction and actuality is not atypical.

The software can still be a valuable tool. You simply 'fool' it by, for example in your case, telling it that the MO is lighter in color than it actually is. This makes the program think it is more alkaline and will demand that you add more acid. Obviously this takes some care and experience with a particular malt but once you have a working set of deceptions in hand you can have pretty good predictions - enough to see, for example, what the consequences of changing base malt percentage from 80 to 85% might be.

The Gypsum also contributes quite a bit to the acidification. If I remove it from the calculations it raises the pH by 0.34.

You do have a lot of calcium (almost 7 mEq/L) but it is unlikely that the pH shift will be as much as 0.34. That would require each mEq of calcium to release approximately 1/2.9 mEq of protons. Kolbach's number, used by most of the programs, was 1/3.5 but what many spreadsheet creators forget (or ignore) is that Kolbach's findings were for German lager beers at knockout. I have always supposed that in the mash tun about half that many protons would be released and recent measurements suggest that that was probably a good guess with the malts checked having factors of at most 1/7 and some 1/10 or less. Thus the actual pH shift attributable to calcium in your case is probably at most 0.14 and more likely 0.10 or less. That is still appreciable, of course.