Question about formulas for estimating final gravity

[slightlyoffbeat]

Hello everyone.

What formula to people use when estimating Final Gravity? I'm interested in finding the most accurate formula available. I understand how to estimate ballpark.

For example, I know that you can get a ballpark estimate using something like:

((1 - (attenuation% * 0.01 )) * GravityPoints)

but my question is this:

1: technically, this calculation won't allow for a FG lower than 1.000. I know that is rare, but it does happen.

2: Does adjuncts like dextrose need to be calculated separately (with a different attenuation %) and then combined after?

3: I've done a ton of reading on adjusting FG from mash temp. I know beersmith has a slope that you can adjust. Anyone have any other methods?

Hopefully others out there like to geek out on formulas and calculations and can point me in the right direction.

Cheers.
Dan

 

[RM-MN]

The accuracy of the formulas doesn't matter much. Once you pitch the yeast, they are in control and they attenuate however much they want to and there is nothing you can do about it. As you mentioned, the formula you cite doesn't allow for gravity to go lower than 1.00 and I've personally had a saison go to 0.997.

 

[theowlman16]

I'm a 30,000 foot brewer. I don't even worry about the thousandths place for gravity.

 

[kwadric]

Much like calculating IBUs, calculating FG is an estimate and often a bad estimate because many factors come into play. I know that this is not technically correct, but when I have beer with simple sugar I assume it is 100% fermentable. So I'd apply the formula you cited but instead of "Gravity Points" I use "Gravity Points not from Simple Sugar."

Here are some links that you might find interesting:

Greg Doss from Wyeast
http://www.homebrewersassociation.o...pdf/2012/1616-04 Attenuation - Gregg Doss.pdf

Woodland
http://www.woodlandbrew.com/2013/01/measured-mash-temperature-effects.html

Kai Trotter
http://braukaiser.com/wiki/index.php?title=Understanding_Attenuation

 

[slightlyoffbeat]

Thanks everyone. I certainly understand that not everyone will be interested in pursuing more accurate formulas, but I enjoy the challenge.

Kwadric, thanks for the links. I have read all of those (great reads), but re-reading them actually lead me to my breakthrough.

The key was apparent vs real attenuation: http://howtobrew.com/book/section-1/yeast/yeast-terminology

When working with something like dextrose, I was using 100% attenuation in my calculations. The calculation actually needs to use the apparent attenuation %, which would be close to 122% (see link above). As soon as I started calculating sugars with 122% and everything else with the average attenuation from the yeast, then my final gravity number started to look more correct. It actually allows the final gravity number to reflect sugars drying out the beer instead of the opposite.

I'm sure I need to study a bit more. There's also mash temperature variables, etc, but at least I am on the right path.

Cheers.

 

[kwadric]

I've implemented the Doss calculation in my home spun recipe calculator. I haven't compared the results versus actual brew log data, but I can see both improvements and flaws when I play around with recipes from Brewing Classic Styles.