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predicting mash pH from beer color and residual alkalinity.

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Kaiser:
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

ndcube:
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.

denny:
Once again, great work and great thanks to Kai.

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

ndcube:

--- Quote from: denny on February 26, 2010, 01:26:22 PM ---I have a question.....what temp is considered room temp?

--- End quote ---

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

Kaiser:

--- Quote from: denny on February 26, 2010, 01:26:22 PM ---I have a question.....what temp is considered room temp?

--- End quote ---

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

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