Author Topic: predicting mash pH from beer color and residual alkalinity.  (Read 1666 times)

Offline Kaiser

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predicting mash pH from beer color and residual alkalinity.
« on: February 26, 2010, 11:18:59 AM »
For a while now I have been thinking how to best estimate mash pH or necessary residual alkalinity from beer color, some grist information and mash thickness. I know John Palmer has this in his water spreadsheet and it is a very popular feature.

I like the idea of giving brewers guidance on what water residual alkalinity to shoot for based on a simple beer parameter like color. It makes sense since mash pH and beer color is largely affected by the color of the grains that are used to brew the beer. Using the data from my mash pH experiments I found that it also matters how much of the color comes from roasted malts and how much comes from crystal or base malts. So I knew that I would need a way to incorporate that somehow into a SRM -> mash pH formula. I also noticed that mash thickness can have a strong impact on mash pH, especially when the residual alkalinity is fairly far away from zero. So I decided to look for a formula that can provide a reasonable accurate mash pH prediction based on beer color, percentage of roasted malt, mash thickness and residual alkalinity.

How I found that formula is described here: http://braukaiser.com/wiki/index.php?title=Beer_color%2C_alkalinity_and_mash_pH which is not so much intended for a broad audience of home brewers. It should be seen as a documentation for interested brewers on how the formula or algorithm was developed which is implemented in my water calculation spread sheet (http://braukaiser.com/documents/Kaiser_water_calculator.xls). At the end it also shows 2 tables that can be used to determine the range of water residual alkalinity that works well for a given beer color, mash thickness and roasted malt percentage.

After having all that I’m curious how well the estimation matches actual data that brewers have seen in home brewing. I rarely calculate beer color for my beers but plan to go back through my records and find a few representative examples.

Kai

Offline ndcube

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Re: predicting mash pH from beer color and residual alkalinity.
« Reply #1 on: February 26, 2010, 01:21:56 PM »
What temperature is your target pH values at on your spreadsheet?

I did a beer a few weeks ago:
SRM = 3
RA = -25
9.5lbs grain (all Pils)
5.5 gal mash water
pH was estimated to be 5.2 using the colorpHast strips (5.5 after error correction).

If you assume room temp then the result I got matches my actual reading.

I'm going to do a Baltic Porter Sunday.  I'll compare the results of that with your spreadsheet as well.

Offline denny

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Re: predicting mash pH from beer color and residual alkalinity.
« Reply #2 on: February 26, 2010, 01:26:22 PM »
Once again, great work and great thanks to Kai.

I have a question.....what temp is considered room temp?
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Offline ndcube

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Re: predicting mash pH from beer color and residual alkalinity.
« Reply #3 on: February 26, 2010, 01:45:17 PM »
I have a question.....what temp is considered room temp?

I guess that can be kind of subjective.  68F.... I think.

Offline Kaiser

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Re: predicting mash pH from beer color and residual alkalinity.
« Reply #4 on: February 26, 2010, 01:49:12 PM »
I have a question.....what temp is considered room temp?

I consider 25 C (77 F) room temp for pH measurements even though lab standard is oftentimes 21 C (70 F). This is because the buffers say that they are accurate at 25C. But the difference of a few degree is not going to cause much of an error.

The pH values from the spreadheet are room temp sample values.

Kai

Offline brewbeard

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Re: predicting mash pH from beer color and residual alkalinity.
« Reply #5 on: February 27, 2010, 08:47:44 AM »
Wow, this is great. I'll be using this for my next brew, a traditional Irish Dry Stout (I know, a bit late for the season).

Water Profile from Ward Labs:

Calcium: 53
Magnesium: 10
Sodium: 37
Sulfate: 9
Chloride: 64
Bicarbonate: 165
Alkalinity: 135

Since it is 70% Marris Otter, 20% Flaked Barley, and 10% Roasted Barley, then the roasted percentage should be 100%, correct?

According to the calculator, then I should hit a mash pH of 5.5, which is perfect.

I'll give this a go when I brew it sometime this week. I only have ColorpHast strips, so the mash pH test won't be that accurate (even accounting for the strip error), but it should tell me if I'm in the ballpark.

Offline dean

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Re: predicting mash pH from beer color and residual alkalinity.
« Reply #6 on: February 27, 2010, 10:22:47 AM »
My strips probably aren't real accurate from what I've read in the forums so I just try to get in the ballpark with what your spreadsheet shows Kai.  I try to take into account that I measure at mash temperature so I expect to see around 5.0 up to 5.3 on my strips, so far its been right around 5.0, guessing if its darker or lighter is just a swag but it looks like maybe 5.1'ish usually.  I like using acid malt too... much easier than ml's or cc's of lactic acid.

I have bigger problems with recipe calculators... none of them seem to be able to predict the SRM very accurately imo.  They work and get in the ballpark so thats okay with me.  Then again, I use the free on-line calculators so maybe the others are better?