When to check mash pH?

[PlinyTheMiddleAged]

First post (long time reader)!

I've been trying to correct problems with my home brew - addressed fermentation temperature, yeast pitch rates, and now water chemistry.

Today I made a Kentucky Breakfast Stout clone using bottled water and a little additional salt (Calcium Chloride and Epsom Salts) to bring the water in line with Bru'n Water's recommended Black Balanced profile. Estimated pH (with no additional acid) was 5.4 - perfect.

I mashed in and checked temperature and pH every 15 minutes from time zero for the duration of the 60 minute mash. I checked temp with a thermapen (checked calibration prior to mash in with ice water and boiling water) and pH with a Hanna pHep model HI 98128 (calibrated last night using 2 point calibration). Here are my pH readings:

0 min - 5.66
15 min - 5.60
30 min -5.54
45 min - 5.48
60 min - 5.46

So, my question is, since the pH varies so much over the course of the mash, what measurement do I target? A pH of 5.66 is way off, but if the 5.46 was important, I got pretty close.

Grain bill (if it matters) was:
13.25 lbs 2 row
12 oz roasted barley (500 L)
12 oz Chocolate (350 L)
8 oz Belgian debittered black (500 L)
8 oz crystal 120
1.5 lbs flaked oats

Mashed with 5.5 gallons of water. Baseline water profile was:
Calcium 20.0 ppm
Magnesium 2.1 ppm
Sodium 20.0 ppm
Iron 0.0 ppm
Bicarbonate 80.0 ppm
Carbonate 0.0 ppm
Sulfate 27.5 ppm
Chloride 3.1 ppm
Nitrate 0.3 ppm
Nitrite 0.0 ppm
Fluoride 0.6 ppm

Added 1.1 grams Epsom Salt and 1.7 gram Calcium Chloride to the 5.5 gallons of mash water prior to mashing in. This brought my targeted profile within spec to:
Calcium target 60.0 ppm - achieved 41.6
Magnesium target 10.0 ppm - achieved 7.3
Sodium target 20.0 ppm - achieved 20.0
Sulfate target 47.0 ppm - achieved 48.1
Chloride target 38.0 ppm - achieved 41.4

So, again, when do I check mash pH to make sure I hit the target of 5.4?

 

[Vigo_Carpathian]

Does that pH meter have temperature compensation? If not, you will get different readings depending on the temperature of the sample.

 

[PlinyTheMiddleAged]

Yes. The meter has auto temperature compensation. However, during the mash, I always removed a few ounces of the wort and cooled it before taking a pH reading. The temperature of the sample was in the 90°-100°F range for all 5 readings.

Thanks!

 

[Vigo_Carpathian]

I usually take a measurement 10 minutes in, and at the end. Typically I'll get a value pretty close to what I started with. The way the readings are trending downward look like mixing may have been an issue. Maybe the mash just needed to be stirred more. Another thing you might wanna do is dough in first at low temps just to get all the grains wet and ready to go. I never do it but it's supposed to result in an extra few points of efficiency. It's weird because with no carbonates and a lot of roasted grains, pH shouldn't be a problem.

 

[VikingChrisColby]

It takes a little while (at least a few minutes) for the starch from the grains to dissolve, and it takes time for the enzymes to convert this starch to sugar. Also, some minerals have a quicker effect on mash pH than others. As such, your mash changes with time and the pH may change from the beginning to the end.
If your mash pH starts high, but finishes in the 5.2–5.6 range (or better yet, in the 5.2–5.4 range), you're fine.

Chris Colby
Editor
beerandwinejournal.com

 

[Tutsbrew]

Does anyone check pH during mashing at all? ...Or should I ask, do very many check it? For me, if the water chem is on target for the grain bill vs. targeted beer style, and we've come to know our mash tun temp characteristics, can't we save money and NOT buy pH testing strips/stuff? Guess I'll keep reading the posts and see what's up. Cheers!

 

[Vigo_Carpathian]

Does anyone check pH during mashing at all? ...Or should I ask, do very many check it? For me, if the water chem is on target for the grain bill vs. targeted beer style, and we've come to know our mash tun temp characteristics, can't we save money and NOT buy pH testing strips/stuff? Guess I'll keep reading the posts and see what's up. Cheers!

I use phosphoric to adjust the pH of my sparge water and test with the meter. I check the mash but mostly out of curiosity because I've never had to adjust it. You can run into astringency issues though it not adjusting the sparge water (especially with fly sparging). If I'm not using much dark malts, I'll throw in a little acidulated malt in the mash for reassurance.

 

[ajdelange]

Estimated pH (with no additional acid) was 5.4 - perfect.

First thing to understand is that accurate pH estimates can only be obtained if you have details of how each of the grist components behaves. Absent that one then has to rely on assumed malt properties based on doing things like assuming that a given malt is more or less like a malt upon which you, or someone else, has made measurements. Doing that with your grist and some data that I have measured and Kai Troester's data on various malts I come up with a mash estimate of 5.40. The fact that the one that you have and mine are very close does not mean that this is the right number but does strengthen the assumption that the actual answer should be close to that.

I mashed in and checked temperature and pH every 15 minutes from time zero for the duration of the 60 minute mash. I checked temp with a thermapen (checked calibration prior to mash in with ice water and boiling water) and pH with a Hanna pHep model HI 98128 (calibrated last night using 2 point calibration).

Have you done the stability check described at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ ? If not you should calibrate your meter just before making the first reading of the day and, if it is not stable, frequently there after, even before each reading if necessary. I have found that the HI 98128 is stable (sample size of 1), in fact very stable if you allow the electrode to equilibrate, but that it is impossible to calibrate properly because it decides when to accept its calibration reading, not you, and it decide that the reading is at equilibrium well before it is. About the best you can do is calibrate, check and adjust subsequent readings by the amount of the error*. Note that the accuracy spec on this meter is 0.05 pH and that is, for the most part, explainable by the calibration problem I mentioned. In any case your unit may perform differently from mine and you need to know how it behaves in order to have confidence in readings from it.

Here are my pH readings:

0 min - 5.66
15 min - 5.60
30 min -5.54
45 min - 5.48
60 min - 5.46

So, my question is, since the pH varies so much over the course of the mash, what measurement do I target? A pH of 5.66 is way off, but if the 5.46 was important, I got pretty close.

It is normal for pH to change rapidly in the first 15 minutes of a mash but usually it drifts upward rather than downward. The changes, -0.06, -0.06, -0.04, -0.02 suggest that thing are coming to equilibrium but you really can't draw too many conclusions unless you are confident that your meter is stable as determined by a stability test. Everything might be just fine here but you want to be confident in that. You can gain confidence in these data by doing a stability check today. If the meter is stable today, it was probably stable the day you brewed.

So, again, when do I check mash pH to make sure I hit the target of 5.4?

Your measurements really answer the question for you. Your pH changed appreciably in the first half hour and then little after that. Thus your mash pH check time should be 20 - 30 minutes into the mash. Note that this is probably too late for you to take remedial action if your pH is off but at least you'll know to do something next time you brew.

Actually, you should do exactly what you did in this brew: check mash pH at several times during the mash so that you will learn what is proper behavior for the beers you brew and how you brew them. In my brewing I expect low initial mash pH and a gradual climb to a certain asymptote. For you a gradual descent may be normal (it depends on whether acids released from one malt are being absorbed by another or conversely). Once you know the curve you will know what to look for and will be able to take corrective action before 20 - 30 minutes.

*What you really should do is calibrate, check the pH in both buffers, determine the errors (don't forget that the buffer pH's are a function of temperature - see the pH Sticky if the package doesn't list this data) and correct subsequent readings with the average of the two. For example if pH 4 buffer reads 4.06 (at a temperature where it's pH is 4) and pH 7 bufffer reads 7.02 (At a temperature at which it is actually at 7) then the errors are +0.06 and + 0.02 and the average is +0.04 so that 0.04 should be subtracted from mash pH readings. The average is being taken because mash pH is about half way between 4 and 7.

 

[PlinyTheMiddleAged]

...Have you done the stability check described at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ ? If not you should calibrate your meter just before making the first reading of the day and, if it is not stable, frequently there after, even before each reading if necessary. I have found that the HI 98128 is stable (sample size of 1), in fact very stable if you allow the electrode to equilibrate, but that it is impossible to calibrate properly because it decides when to accept its calibration reading, not you, and it decide that the reading is at equilibrium well before it is. About the best you can do is calibrate, check and adjust subsequent readings by the amount of the error*. Note that the accuracy spec on this meter is 0.05 pH and that is, for the most part, explainable by the calibration problem I mentioned. In any case your unit may perform differently from mine and you need to know how it behaves in order to have confidence in readings from it.

I did not do the stability check. I simply took the unit out of the box, immersed the probe in the storage solution for an hour or so and then performed the calibration steps using the 4.01 and 7.01 pH buffers.

*What you really should do is calibrate, check the pH in both buffers, determine the errors (don't forget that the buffer pH's are a function of temperature - see the pH Sticky if the package doesn't list this data) and correct subsequent readings with the average of the two. For example if pH 4 buffer reads 4.06 (at a temperature where it's pH is 4) and pH 7 bufffer reads 7.02 (At a temperature at which it is actually at 7) then the errors are +0.06 and + 0.02 and the average is +0.04 so that 0.04 should be subtracted from mash pH readings. The average is being taken because mash pH is about half way between 4 and 7.

I checked the pH readings of the buffers again today. I checked both the 4.01 and 7.01 buffers three times at three hour intervals. At each interval, I measured the buffer pH three times. First interval average results were 4.16 and 7.21; second interval 4.24 and 7.28; third interval 4.20 and 7.29. Overall averages were 4.20 (+0.19 high) and 7.23 (+0.22 high) or using the average of the averages, the meter was reading +0.21 high. It appears that the calibration drifted overnight. I'm not surprised since that was a first use of the meter - I probably rushed the "priming" of the bulb with the storage solution. Next time, I'll make sure the bulb is well primed with the storage solution for at least a day prior to use and I'll calibrate it just prior to use.

And I assume that the pH drifted down on this wort due to the load of roasted malts that I used - as the acids were drawn out of the grain during the mash, the pH dropped. But if I adjust yesterday's readings by the +0.21 offset, my mash pH must have been 5.45, 5.39, 5.33, 5.27, and 5.25 at 0, 15, 30, 45, and 60 min, respectively. I think I was close to the target pH.

Thanks all! Terrific world class help on this forum.