Author Topic: How BeerSmith calculates recipe SRM  (Read 6289 times)

Offline dennydeaton

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How BeerSmith calculates recipe SRM
« on: December 07, 2011, 07:16:29 AM »
Hi,

I've read through the related posts on this forum (and others).  I also saw the related BeerSmith blog from 2008. But still haven't found a clear answer as to how BeerSmith calculates the total SRM for a recipe.  I know it uses Morey's Formula, but I'm unsure of the exact MCU calculation it inputs and how it derives that from the grain data.  I want a better understanding of how this works.

Here is a simple example that I went through and calculated it manually. I also ran the same ingredients through BeerSmith but the results are not matching up.  Could anyone tell me the discrepancy?

volume (post-boil): 7.02
grain1: 5lbs @ 2.0SRM (American 2-row)
grain2: 2lbs @ 23.0SRM (Biscuit Malt)

For reference: SRM = 1.4922 [(MCU) ^ 0.6859]

1.4922 * ((5*2)/volume) ^ 0.6859) = 1.90206086681
1.4922 * ((2*23)/volume) 0.6959) = 5.5204466145

1.90206086681 + 5.5204466145 = 7.42 SRM

Beersmith calculates the same ingredients at 6.4 SRM

Offline BeerSmith

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Re: How BeerSmith calculates recipe SRM
« Reply #1 on: December 07, 2011, 01:43:30 PM »
Hi,
  You need to total the MCU up first - so add 5*2 + 2*23 = 56 and then you apply the equation and you will get about 6.3 if my hand calculator is correct.

Brad
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Offline dennydeaton

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Re: How BeerSmith calculates recipe SRM
« Reply #2 on: December 07, 2011, 02:01:53 PM »
Thank you for the reply.  That was helpful.

I checked the BYOCalc spreadsheet (http://www.byo.com/stories/article/indices/28-computer-brewing/1690-write-your-own-brewing-spreadsheet) as well, which calculated it like I had originally.  I certainly don't doubt your research, but I'm trying to determine which way is correct.

What caused you to compile the (Weight/SRM) for each ingredient and add them up before running them through Morey's Formula?

Offline BeerSmith

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Re: How BeerSmith calculates recipe SRM
« Reply #3 on: December 07, 2011, 04:16:56 PM »
I tell you what - I will contact Dan Morey himself via email and see what he has to say!

Brad
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Offline dennydeaton

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Re: How BeerSmith calculates recipe SRM
« Reply #4 on: December 08, 2011, 08:09:24 AM »
Perfect!  Thanks, Brad.

I've spent more time looking at the numbers and it seems like your method is best, as it is truer the curve-fitting.

Offline BeerSmith

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Re: How BeerSmith calculates recipe SRM
« Reply #5 on: December 08, 2011, 09:44:15 AM »
Hi,
  I got a message back from Dan Morey (author of the Morey equation) and he confirmed that my method is the correct one.  You total up the MCU contributions from the grains before applying the Morey equation.

Brad
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Offline dennydeaton

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Re: How BeerSmith calculates recipe SRM
« Reply #6 on: December 08, 2011, 11:03:32 AM »
Hi Brad,

Great, thanks for the follow-up.