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Old 03-24-2012, 05:13 PM   #1
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Default pH Rises over time?

It's been awhile since I have frequented the brew science forum. In the time since I first came here with high alkalinity issues with my local water supply, I have purchased a basic pH meter and some of the basic ingredients for adjusting the pH of my water down (gypsum, CaCl, and acid malt). I've used the spreadsheets available on this forum and toyed with a mix of my own water and distilled water depending on the style (anywhere from 100% to 70%).

I have been able to consistently get my worts in the 5.2-5.6 pH range. The beers have been noticeably better (especially my lighter beers). But one trend has emerged and I wonder if it is anecdotal, or expected.

I usually take my mash pH at around 5 min into the mash, then every 15 min for the remainder of my mash (60-90 min total depending on style). I have noticed that the pH of the mash tends to rise about .1 on each successive reading, but never more than .2 to .3 over the course of the mash. The precision of my meter is only .1 so the change may be larger than that. But it seems to be fairly consistent.

My assumption is that as the enzymes go to work and the starch to sugar conversion takes place that the pH of the wort will change correspondingly. But that is only an uneducated guess on my part.

Does this sound right or is something else at work?

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Old 03-24-2012, 07:30 PM   #2
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I don't know what the mechanism is but upwardly creeping pH over the course of an hour or more seems to be normal. In a recent attempt to determine the DI mash pH of Weyermann's Pilsner malt I observed the following

Time after dough in------------pH
1.5 min ________________5.40
4.7 min ________________5.45
11.1 min________________5.49
15.6 min________________5.54
26.23 min______________5.58
35.5 min________________5.59

This was done at about 120 °F. In another experiment at room temperature it took over an hour for mash pH to climb from 5.46 to 5.71. So the observation that mash pH rises over time seems valid and 0.2 - 0.3 seems a valid range.

I'm trying to predict mash pH. I need to know DI pH and titratable alkalinity. When do I take my pH measurments?

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Old 03-24-2012, 07:40 PM   #3
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Thanks for the reply aj. That tracks with the beer I am making today (cream ale, currently in the boil). I took readings at 15, 30 and 50 min into a 90 min mash. I get 5.3, 5.4 and 5.5 Although as long as the last reading took to come down from 5.6 to 5.5, it was probably closer to 5.6.

The malt bill was 6.5# 2-row, 2# flaked corn and 1# of flaked rice (with 1# of rice hulls to help with lautering). The mash was 90min at 152F. Going for a light summer ale. My water was 100% store bought "drinking water" (they did not have distilled).

I added 1 tsp each of CaCl and gypsum to the mash and sparge water. With a bill like that and all bottled water, I expected a lower pH. My meter read 4.0 and 7.0 on the dot in the calibration solutions. All measurements were taken at 65F.

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Old 03-25-2012, 03:33 PM   #4
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Quote:
Originally Posted by winvarin View Post
Thanks for the reply aj. That tracks with the beer I am making today (cream ale, currently in the boil). I took readings at 15, 30 and 50 min into a 90 min mash. I get 5.3, 5.4 and 5.5 Although as long as the last reading took to come down from 5.6 to 5.5, it was probably closer to 5.6.

The malt bill was 6.5# 2-row, 2# flaked corn and 1# of flaked rice (with 1# of rice hulls to help with lautering). The mash was 90min at 152F. Going for a light summer ale. My water was 100% store bought "drinking water" (they did not have distilled).
5.6 isn't that surprising for that grain bill, without acid of some sort, in my opinion. I did a tripel yesterday. It was 13.5lbs Weyermann Pilsner, 6 ounces carmel pilsner (This is a ~5-10L crystal, not carapils.), 2 ounces special b, and 2.5 pounds corn sugar (obviously not in the mash). I had my calcium at about 50ppm and my alkalinity at about 53 (so probably a bit above your alkalinity). I added 2.5ml of lactic acid in my mash (6 gallons of water) and ended up with a pH of 5.42.
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Old 03-25-2012, 03:39 PM   #5
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I've only used acid malt for ph adjustment beyond the cacl or gypsum. If you use lactic acid, is it added to the mash water? Or do you stir it directly into the mash once you've taken your first ph reading?

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Old 03-25-2012, 03:56 PM   #6
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I've only used acid malt for ph adjustment beyond the cacl or gypsum. If you use lactic acid, is it added to the mash water? Or do you stir it directly into the mash once you've taken your first ph reading?
I added it to the mash water before I added my grain. I did, however, do a sample mash to get an idea of where my mash pH would be without any acid.

EDIT: P.s. I don't recommend licking your finger if you accidentally get a little lactic acid on it...OMG, sour
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Old 03-25-2012, 04:18 PM   #7
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Is there anything in the conversion from starch to sugar that would account for something like this?

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Old 03-25-2012, 05:42 PM   #8
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Quote:
Originally Posted by winvarin View Post
I've only used acid malt for ph adjustment beyond the cacl or gypsum. If you use lactic acid, is it added to the mash water? Or do you stir it directly into the mash once you've taken your first ph reading?
That would depend on whether it is a standard or corrective addition. IOW if you know, by experience, that a particular recipe takes 10 mL of lactic acid then you can just put it in the mash water and mix it in well. That gives you a leg up and getting it evenly distributed over the mash. If, OTOH, you dough in, wait 10 or 15 minutes and find that your mash pH is too high then you would have to add it incrementally to the mash. Very vigorous stirring is required at that point to get it dispersed evenly.
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Old 03-25-2012, 05:43 PM   #9
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Quote:
Originally Posted by afr0byte View Post
EDIT: P.s. I don't recommend licking your finger if you accidentally get a little lactic acid on it...OMG, sour
I like to chew on a bit of the malt. It is reasonably high kilned and so a bit sweet. That plus the tart makes it pretty tasty (IMO).
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Old 03-25-2012, 05:48 PM   #10
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Quote:
Originally Posted by Hermit View Post
Is there anything in the conversion from starch to sugar that would account for something like this?
No. That's a simple hydrolysis: -C-O-C- + H2O ----> -C-OH + OH-C -
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