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Old 09-05-2009, 04:57 PM   #1
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Default Predicting attenuation?

Hi all,

Are there formulas for predicting the apparent attenuation of a beer, give the estimated attenuation characteristics of the yeast being used, mash temperature and grain bill? I know that there are other factors that come into play - pitching rates, fermentation temps, etc. - but I'm looking for something just a little more sophisticated than multiplying the OG by the apparent attenuation characteristics stamped on the yeast packet.

This would be useful for setting the mash temp when developing recipes.

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Old 09-05-2009, 11:15 PM   #2
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The info stamped on the yeast is there for a reason. It's pretty much what you should expect. Taking the OG and the yeast's known attenuation is going to tell you what you need so I'm not sure why you feel the need for any other method. You could achieve results besides what the package says but I believe your best bet is to try and figure out how to hit the exact percentage on the package. Work on your process so that it lines up with what the yeast is designed to do. Knowing what you're going to get before you start is what will help you design the right recipe!

Hope this helps.

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Old 09-06-2009, 12:36 AM   #3
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Originally Posted by cvstrat View Post
The info stamped on the yeast is there for a reason. It's pretty much what you should expect. Taking the OG and the yeast's known attenuation is going to tell you what you need so I'm not sure why you feel the need for any other method. You could achieve results besides what the package says but I believe your best bet is to try and figure out how to hit the exact percentage on the package. Work on your process so that it lines up with what the yeast is designed to do. Knowing what you're going to get before you start is what will help you design the right recipe!

Hope this helps.
No, it doesn't help at all.

Clearly the yeast's attenuative properties are a significant factor (I said that in my original post) but there's much more to it than that. A beer that is mashed at 148 dgf is going to finish much drier than a batch that's mashed at 155. Mash a beer at 170 and you'll get almost no attenuation, no matter what's printed on the yeast packet. Similarly, the FG of a wort made entirely of pale malt will be lower than that of a wort with lots of carafoam in it; a wort with lots of corn sugar will finish lower.

Maybe these equations don't exist yet, but we should be able to do better than just using estimated yeast attenuation and OG to predict FG. I suspect that there's an equation or table floating around that at least factors in mash temp.

TD
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Old 09-06-2009, 12:51 AM   #4
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No, it doesn't help at all.
"....thanks, though"? Sounds a bit rude otherwise

If you knew the exact amounts of fully-fermentables and partially-fermentables and the attenuative power of the yeast and the exact temperature you mashed at (minute by minute, unless you held a single temp for the whole time) and exactly how much fermentables you will get at that temperature and how much attenuation you should expect from the yeast at whatever temperature you ferment at and....

Should I go on?
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Old 09-06-2009, 02:48 AM   #5
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Originally Posted by Reno_eNVy_446 View Post
"....thanks, though"? Sounds a bit rude otherwise

If you knew the exact amounts of fully-fermentables and partially-fermentables and the attenuative power of the yeast and the exact temperature you mashed at (minute by minute, unless you held a single temp for the whole time) and exactly how much fermentables you will get at that temperature and how much attenuation you should expect from the yeast at whatever temperature you ferment at and....

Should I go on?
I think that's what the OP is trying to ask, if there is something out there that could take all of these variables into account and spit out an answer. It would be great if one of the programs(Beersmith, promash, Beer tools, etc.) could upgrade to handle this calculation. just a thought.
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Old 09-06-2009, 03:53 AM   #6
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Originally Posted by Reno_eNVy_446 View Post
If you knew the exact amounts of fully-fermentables and partially-fermentables and the attenuative power of the yeast and the exact temperature you mashed at (minute by minute, unless you held a single temp for the whole time) and exactly how much fermentables you will get at that temperature and how much attenuation you should expect from the yeast at whatever temperature you ferment at and....

Should I go on?
You could say the same thing about the formulas we use to estimate OG, bitterness, color, or any other part of the brew process. Just because we don't know every last bit of information about our processes doesn't mean that equations or tables for estimating these processes can't deliver good approximations.

The point is that we do know that mash temps have a significant influence on the FG, and in general what those influences are. We can also do a reasonable job of estimating mash temp, even if it's just the average temp over the duration of the mash. I'm surprised that there aren't formulas available that factor this in.

Does beersmith, promash or any other brewing tool estimate FG? Does varying the mash temp have an effect in these tools?
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Old 09-06-2009, 01:30 PM   #7
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So I found a couple of excellent resource:

and on Kaiser's site (Thanks Kai!):Based on Kai's research we should be able to develop an equation to estimate FG based on OG, yeast attenuative properties and avg. mash temp (assuming a single infusion mash.) Of course this doesn't take into account mash length, grain bill, or anything else, but it should give us a little more accuracy than leaving the temps out.

I'll take a shot at fitting an equation to Kai's data. It's been over 15 years since I did one; hopefully I won't embarrass myself.
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Old 09-06-2009, 05:03 PM   #8
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I was able to fit a rough curve to Kai's experimental data for attenuation vs. avg. mash temp to come up with a correction factor to attenuation for single infusion mashes:

For avg. mash temps (T) in deg C

mf=-.0030*T^2+.3904*T-11.699
Note that mf=~1.0 for a mash temp of 66C, less than 1 for other values. This fits reasonably well with the data in the range 60C to 75C

For avg. mash temps (T) in deg F
mf=-.000926*T^2+.2761*T-19.582
Note that mf=~1.0 for an avg. mash temp of 150.5F, less than 1 for other values. This fits reasonably well with the data in the range 140dgF to 167dgF

This factor can be applied to the standard SG estimate:

SG = (1-mf*AA)*OG

Where AA is the optimal apparent attenuation of the yeast.

Below is the correction factor applied to Kaiser's data. Note that I have taken the optimal apparent attenuation as 90.5%, the average of the two data points at 65.9C
Code:
Batch   temp C   OG    SG    AA%     mf    calc SG
  12     59.9   13.0   2.4   81.5   0.922     2.2
  11     61.9   10.2   1.2   88.2   0.972     1.2
  10     63.3   11.7   1.1   90.6   0.993     1.2
   8     65.9   11.8   1.3   89.0   1.000     1.1 
   9     65.9   11.2   0.9   92.0   1.000     1.1
   7     69.3   14.0   2.1   85.0   0.948     2.0
   2     70.5   13.1   2.6   80.2   0.914     2.3
  15     71.0   16.5   3.8   77.0   0.897     3.1
  13     74.7   15.4   5.0   67.5   0.724     5.3
   6     74.9   13.5   5.0   63.0   0.712     4.8
  14     78.6   16.7   8.9   46.7   0.453     9.9
What do you folks think, am I on to something here?
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Old 09-08-2009, 12:13 AM   #9
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Originally Posted by ToledoDave View Post
Code:
Batch   temp C   OG    SG    AA%     mf    calc SG
  12     59.9   13.0   2.4   81.5   0.922     2.2
  11     61.9   10.2   1.2   88.2   0.972     1.2
  10     63.3   11.7   1.1   90.6   0.993     1.2
   8     65.9   11.8   1.3   89.0   1.000     1.1 
   9     65.9   11.2   0.9   92.0   1.000     1.1
   7     69.3   14.0   2.1   85.0   0.948     2.0
   2     70.5   13.1   2.6   80.2   0.914     2.3
  15     71.0   16.5   3.8   77.0   0.897     3.1
  13     74.7   15.4   5.0   67.5   0.724     5.3
   6     74.9   13.5   5.0   63.0   0.712     4.8
  14     78.6   16.7   8.9   46.7   0.453     9.9
I have been trying for the past 20 minutes to figure out what "mf " stands for. Mash something?
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Old 09-08-2009, 01:12 AM   #10
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I have been trying for the past 20 minutes to figure out what "mf " stands for. Mash something?
Sorry - I was thinking 'mash factor', but it's really just an arbitrary symbol.
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