Author Topic: Final Gravity Estimation  (Read 1783 times)

Offline Phil_M

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Final Gravity Estimation
« on: June 15, 2016, 12:58:59 AM »
Aside from gathering data from prior batches, what is the best way to try and estimate final gravity when planning out a beer?

I know from experience that some of Wyeast's strains are far more attenuative than their fact sheets imply, so simply using their attenuation percentages doesn't work. Clearly mash temps factor into all this as well.

What's driving this question are the two beers I've got fermenting right now. Brewed a 10g batch of best bitter on Sunday, split it into two carboys and pitched Wyeast 1968 in one, 1318 in the other. Right now the 1318 is at 1.014, while the 1968 is at 1.011. I'm hoping they both finish in the mid-upper single digits for FG, and it occurred to me that I don't have any real idea what to expect them to finish at.

Mash was 152 for 90 minutes, final temp was 149, FWIW. 93% MO, 5% Crystal 60L, 2% Chocolate.
Corn is a fine adjunct in beer.

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Offline HoosierBrew

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Re: Final Gravity Estimation
« Reply #1 on: June 15, 2016, 01:19:00 AM »
Wish I had better news, Phil. But IME the only way is to keep good notes for future reference. If you happen to nail the FG you like on a beer, try to repeat everything identically including yeast strain (though differences in yeast viability and other factors can make that tricky at times). If you want to finish a tad higher or lower but like the flavor as is, mashing a tad higher or lower is the way to go. Obviously changes to the grist, ie., more or less crystal or roasted malts play a role as well. Still takes me trial and error. Keep good notes.
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Offline Phil_M

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Re: Final Gravity Estimation
« Reply #2 on: June 15, 2016, 01:30:54 AM »
Wish I had better news, Phil. But IME the only way is to keep good notes for future reference. If you happen to nail the FG you like on a beer, try to repeat everything identically including yeast strain (though differences in yeast viability and other factors can make that tricky at times). If you want to finish a tad higher or lower but like the flavor as is, mashing a tad higher or lower is the way to go. Obviously changes to the grist, ie., more or less crystal or roasted malts play a role as well. Still takes me trial and error. Keep good notes.

That's kinda what I expected to hear. Still, there's got to be something better than the Beersmith guesstimates...

If these beers finish higher than I want I might consider dosing them with some invert syrup later in fermentation...would that work?
Corn is a fine adjunct in beer.

And don't buy stale beer.

Offline HoosierBrew

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Re: Final Gravity Estimation
« Reply #3 on: June 15, 2016, 01:36:44 AM »
Yeah, those software estimates are worthless. Just too many combos of yeast strain, grist, and mash parameters to nail down a perfect FG number. And yeast estimates put out by yeast companies aren't much better, and software uses those estimates as part of its own estimate.
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Offline Erik_Mog

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Re: Final Gravity Estimation
« Reply #4 on: June 15, 2016, 01:49:40 AM »
Yeah, those software estimates are worthless. Just too many combos of yeast strain, grist, and mash parameters to nail down a perfect FG number. And yeast estimates put out by yeast companies aren't much better, and software uses those estimates as part of its own estimate.

And the numbers that the software uses are often nowhere near what the manufacture states.  Case in point, Beersmith says WB-06 has an attenuation of 68% (66%-70%). The spec sheet from Fermentis says 86% max attenuation.  I just used WB-06 in a Hefe, making the mistake of trusting the software, and got 83% apparent attenuation.  If BeerSmith had even close to accurate numbers for the yeast, my Hefe would have been around 4.4% ABV and now it is 5.4%.
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Offline Phil_M

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Re: Final Gravity Estimation
« Reply #5 on: June 15, 2016, 01:56:12 AM »
Yeah, those software estimates are worthless. Just too many combos of yeast strain, grist, and mash parameters to nail down a perfect FG number. And yeast estimates put out by yeast companies aren't much better, and software uses those estimates as part of its own estimate.

Exactly. Maybe we need some sort of home brewer database, with mash temps/times, grain categories (just into base, crystal and roast, like Bru'n water?) etc. Then geek out with the data and estimate some outcomes. Might even be able to revise the attenuation predictions that Wyeast and WL give out.
Corn is a fine adjunct in beer.

And don't buy stale beer.

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Re: Final Gravity Estimation
« Reply #6 on: June 15, 2016, 02:29:48 AM »
Add in the fact that Trappist beers, with large portions of sugar as fermentables, yield mid to high 80s in attenuation and you've got variables galore.

Offline Pricelessbrewing

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Re: Final Gravity Estimation
« Reply #7 on: June 15, 2016, 03:53:11 AM »
Completely agree about everything said so far.

An attenuation database would be interesting, but it could get very complicated as stated before due to variable mash temps and grain bills. You'd have to calculate out the difference in fermentability of the given grain bill, and try to adjust it to a known standard like 100% 2row. Could be difficult/impossible to get right.

IMO the best case is to do a forced fermentation test and try it out yourself. Bonus round: You're making a starter right? Record the og and fg and see what the attenuation is !

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Re: Final Gravity Estimation
« Reply #8 on: June 15, 2016, 04:12:50 AM »
What's worse, I've been gathering data over the past couple years and there are at least two (maybe three, the correlation's weak) yeast phenotypes at play. Not only will two strains likely not attenuate the same wort to the same degree, they may not even exhibit the same *trend* in fermentability as a function of temperature.
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Offline blair.streit

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Re: Final Gravity Estimation
« Reply #9 on: June 15, 2016, 07:54:15 AM »
What's worse, I've been gathering data over the past couple years and there are at least two (maybe three, the correlation's weak) yeast phenotypes at play. Not only will two strains likely not attenuate the same wort to the same degree, they may not even exhibit the same *trend* in fermentability as a function of temperature.
Well that's depressing. It might also contribute to some experiences I've had where ramping temp too early on WLP833 seemed to stall it out around in the mid 60's ADF on grain bill and mash temp combos where I've seen it attenuate in the mid 70's with different temp ramping.

Offline texaswine

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Re: Final Gravity Estimation
« Reply #10 on: June 15, 2016, 10:13:56 AM »
Aside from gathering data from prior batches, what is the best way to try and estimate final gravity when planning out a beer?

I know from experience that some of Wyeast's strains are far more attenuative than their fact sheets imply, so simply using their attenuation percentages doesn't work. Clearly mash temps factor into all this as well.

What's driving this question are the two beers I've got fermenting right now. Brewed a 10g batch of best bitter on Sunday, split it into two carboys and pitched Wyeast 1968 in one, 1318 in the other. Right now the 1318 is at 1.014, while the 1968 is at 1.011. I'm hoping they both finish in the mid-upper single digits for FG, and it occurred to me that I don't have any real idea what to expect them to finish at.

Mash was 152 for 90 minutes, final temp was 149, FWIW. 93% MO, 5% Crystal 60L, 2% Chocolate.
Fast Ferment Test (FFT).

http://braukaiser.com/wiki/index.php?title=Fast_Ferment_Test

Offline Phil_M

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Re: Final Gravity Estimation
« Reply #11 on: June 15, 2016, 10:41:26 AM »
Fast Ferment Test (FFT).

http://braukaiser.com/wiki/index.php?title=Fast_Ferment_Test

While that would have helped me understand where these beers will finish, the goal is to have a rough idea where they'll finish before the beer is brewed. After your recipe is locked in, a fast ferment test (Still can't bring myself to call them FFTs, there's no domain to change...) only really shows you if you screwed up or not. Which at least in my brewing to date the final beer also tells me. It'll help the next batch, but not that initial batch.
Corn is a fine adjunct in beer.

And don't buy stale beer.

Offline pete b

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Re: Final Gravity Estimation
« Reply #12 on: June 15, 2016, 11:12:05 AM »
I don't worry too much about the number any more. I seem to be able to hit the same numbers when doing more or less the same recipe but when I hit a software prediction spot on I don't rejoice because I know the next new recipe I could be just as precise and be 8 points off. Furthermore, a beer with a similar OG that finishes at 1.016 could taste as dry as a beer that finishes at 1.010.
I keep a couple variables the same virtually every time: a healthy pitch of yeast into well aerated wort and a ramp up in temperature after a couple days in primary.
After that I seem to get the best bang for my buck manipulating grist, including sugar. If I make an IPA with no or little crystal (80% pale, 20% Munich for instance) and a little sugar, I know I will be dry and not overly sweet as I like it, even if my FG number isn't what I expected.
It's really about taste and mouthfeel and not the number,assuming nothing is way off. I have had a porter finish in the high 1.020's and not taste under attenuated and porters finish at 1.010 with 1450 that had a nice malty flavor and creamy mouthfeel.
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Offline denny

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Re: Final Gravity Estimation
« Reply #13 on: June 15, 2016, 04:33:26 PM »
Aside from gathering data from prior batches, what is the best way to try and estimate final gravity when planning out a beer?

I know from experience that some of Wyeast's strains are far more attenuative than their fact sheets imply, so simply using their attenuation percentages doesn't work. Clearly mash temps factor into all this as well.

What's driving this question are the two beers I've got fermenting right now. Brewed a 10g batch of best bitter on Sunday, split it into two carboys and pitched Wyeast 1968 in one, 1318 in the other. Right now the 1318 is at 1.014, while the 1968 is at 1.011. I'm hoping they both finish in the mid-upper single digits for FG, and it occurred to me that I don't have any real idea what to expect them to finish at.

Mash was 152 for 90 minutes, final temp was 149, FWIW. 93% MO, 5% Crystal 60L, 2% Chocolate.

Yeast attenuation rating is useful for comparing one yeast to another using a standardized wort, but that's about it.  The attenuation you can expect is based pretty much on the wort you make.  Using the same yeast but different worts, I can get from 65-85% attenuation.
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Offline Pricelessbrewing

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Re: Final Gravity Estimation
« Reply #14 on: June 15, 2016, 08:32:48 PM »
What's worse, I've been gathering data over the past couple years and there are at least two (maybe three, the correlation's weak) yeast phenotypes at play. Not only will two strains likely not attenuate the same wort to the same degree, they may not even exhibit the same *trend* in fermentability as a function of temperature.

This is exactly what I've thought. Ive noticed it with phenolic saison/Belgians and non phenolic saison like strains (hefes included).

Would you be able to send me any data you have?

I wish yeast companies would be able to publish datasets like this, would be fun to look at. Can the strain I'm looking at break down   some dextrins for example?