Author Topic: FG predictions usually high  (Read 5777 times)

David Oldenburg

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FG predictions usually high
« on: May 02, 2005, 05:51:37 PM »
Lately, my beers have been fermenting out much further than Beersmith predicts.  I realize that this isn't an exact science, but how does Beersmith predict this?

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Re: FG predictions usually high
« Reply #1 on: May 02, 2005, 11:58:05 PM »
David,
 The FG is estimated based on the original gravity estimate and also the average attenuation of the yeast you have chosen (from the manufacturer's specs).

 As many have noted this is not perfect because so many other factors affect final gravity (including temperature of fermentation, ingredients and adjuncts used, mashing temperature, etc...).  However, for the moment it is the best formula I have available to me.

 If anyone is aware of a better formula for estimating FG I would be happy to include it.

Cheers!
Brad

« Last Edit: May 02, 2005, 11:58:32 PM by admin »
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Offline doldenburg

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Re: FG predictions usually high
« Reply #2 on: May 03, 2005, 04:02:18 AM »
Does it take into account how much of the OG is from malts like crystal, black, etc. that contribute only unfermentable extract?  If not, you could add that to the formula and probably get slightly more accuracy.

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Re: FG predictions usually high
« Reply #3 on: May 03, 2005, 02:22:42 PM »
No,
 It does not - I do not have any empirical data to back up how much fermentable/unfermentables it adds, or what portion on average is actually fermented.

 If you have some good references, that would be great.

Cheers!
Brad
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Offline bonjour

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Re: FG predictions usually high
« Reply #4 on: May 03, 2005, 04:34:10 PM »
Because I brew really big beers I look at predicting FG.  It is part art and part science.  The science part BeerSmith has down pretty good, the Art, that factors in the many points that Brad mentioned.  The concensus is that there is no info available on predicting FG.  If you brew what I term century brews (OG's >> 1.100) you have to learn what factors impact FG. You do not want a high FG brew.  When you brew monsters you want a highly fermentable, high attenuation beer.

Fred
« Last Edit: May 04, 2005, 02:04:29 AM by bonjour »

Offline Orval

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Re: FG predictions usually high
« Reply #5 on: June 29, 2011, 02:35:52 AM »
No,
  It does not - I do not have any empirical data to back up how much fermentable/unfermentables it adds, or what portion on average is actually fermented.

  If you have some good references, that would be great.

Cheers!
Brad

I have analysed 60 of my brews and have come up with a pretty accurate formula. In most cases the formula predicts the final gravity within 2 SG points.

The formula is:

Est. Apparent attentuation = 0.00825*MAy+0.00817*MTh-0.00684*MTemp+0.000256*MTime-0.00356*%C+0.00553*%S+0.547

MAy = Maximum apparent attenuation of the yeast as given by the manufacturer
MTh = Mash thickness in liters of water per kg of malt+adjucts
MTemp = Mean mash temperature in Deg. Celcius
MTime = Total mash time in minutes
%C = Percentage of crystal or cara malts in the grist (0-30)
%S = Percentage of simple sugars in the grist (0-30)

The mean mash temperature is calculated as the weighted average over the period the mash was over 60 deg. C.

This formula might only work in my brewing setup and implicitly assumes that enough healthy yeast has been added and the fermentation conditions were optimal.

But as I said, this formula predicts my final gravities within 2 gravity points, unless there is something wrong with my yeast(starter) or fermentation.
« Last Edit: June 29, 2011, 06:32:21 AM by Orval »