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Home Brew Forums > Home Brewing Beer > Brew Science > Unsure about your RA target, do a test mash
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Old 06-24-2009, 04:16 AM   #1
Kaiser
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Default Unsure about your RA target, do a test mash

This may be going to far for most, but last weekend I brewed a recipe that I hadn't brewed in a while and was wondering about the residual alkalinity that I should aim for to get to a pH between 5.4 and 5.5. When I weighed out the grain I also used my gram scale to weigh out a 1oz (30g) version of the grist. I ground that up with a coffee grinder and mixed it with distilled water at the targeted mash thickness and at about 75F. I then tested the pH of that mash and found that it was 5.51.

If I wanted to get to 4.5 I needed to lower the pH by about 0.6 units. And since each ppm alkalinity as CaCO2 changes the pH by about 0.0018 pH I needed to lower the RA by 33 ppm as CaCO3. Distilled water has an RA of 0 and therefore my RA target was -30..-35 ppm as CaCO3.

I did this and low and behold my mash pH ended up at 5.46 (+/- 0.02).

This might be too much geekery for many but I actually liked this idea of determining the RA target. I could have also found an RA that would get me close based on previous beers with a similar grist and then prepared to correct it in the mash but I like the idea of not having to be in a rush during mashing.

I also mashed with cold water for the test mash. It seems that the result was in line with the actual mash but I'm not sure if this will be true for all types of grain. Roasted grains may not "dissolve" properly in cold water and making a hot test mash would have been too much hassle for me.

Kai



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Old 06-24-2009, 01:12 PM   #2
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So, you couldn't sleep last night..
Seriously, this is very good stuff, and I think I'll try this on my next brewing day. I might try to build the receipt in miniature meaning the base grain will be no larger then 1 oz and the balance of the grains being the appropriate % of weights. Then I think I will mash at the proper temperature and take a Ph reading. This could be a great way to determine the Ph before starting the mash and not to have to go through a hurried hassle on brew day.

thanks

tom


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Old 06-24-2009, 04:26 PM   #3
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This is great stuff kaiser. Also, great stuff on your site too!

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Old 06-24-2009, 08:07 PM   #4
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Wouldn't a cold mash affect phytase activity and, therefore, the mash pH? Offhand, I'm not sure of the difference in phytase activity at 75F vs. 140+F, so maybe they're close.
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Old 06-24-2009, 09:20 PM   #5
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Quote:
Originally Posted by menschmaschine View Post
Wouldn't a cold mash affect phytase activity and, therefore, the mash pH? Offhand, I'm not sure of the difference in phytase activity at 75F vs. 140+F, so maybe they're close.
Taken from Kaisers page:


Understanding Mash pH - German Brewing Techniques

Temperature dependency of the pH measurement

The pH of a solution changes with its temperature. This needs to be taken into account when measuring the pH and determining what the pH target is. Some authors cite the pH ranges and targets at the actual reaction temperature (i.e. rest temperature) and others cite the pH values as if measured in a cooled sample. The latter makes sense since it is a good practice to cool a sample before measuring it with a pH meter. It also gives a common reference and allows for giving pH values without the need of giving a temperature as well. Unless otherwise noted, all pH values on this wiki are pH values measured at room temperature (25 C). To make matters even worse, the temperature dependency of the pH is also dependent on the substrate itself. Briggs quotes a difference of 0.35 in pH between a mash pH measured at mash temps and the same liquid measured at room temp. The pH measured at mash temp is lower [Briggs, 2004].
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Old 06-24-2009, 11:21 PM   #6
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humann, that has to do with measuring mash pH (i.e., removing the sample and cooling it prior to taking the pH measurement), not setting mash pH. My question is regarding phytase activity at a 75F mash vs. a "normal" mash.
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Old 06-25-2009, 03:05 PM   #7
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There is a slight pH difference between a 25C mash and a hot mash cooled to 25C. But it seems to be in the order of +/- 0.05 pH units. Good enough for a quick test. Making a hot test mash would have been to much work.

Kai
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Old 06-25-2009, 03:13 PM   #8
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Quote:
Originally Posted by menschmaschine View Post
humann, that has to do with measuring mash pH (i.e., removing the sample and cooling it prior to taking the pH measurement), not setting mash pH. My question is regarding phytase activity at a 75F mash vs. a "normal" mash.
I see, my bad. I have only been looking at water adjustments for about 2 weeks now and trying to plan my next batch with water adjustments. So I am still figuring this stuff out. Thanks.


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