Final Gravity - Estimation?

[amcd72]

I have been a lurker for a little bit now. Been taking in lots in info and reading lots of different recipes (getting myself ready for AG).

Got a question about the FG number that sits in the recipe details...
How do you come up with the FG figure before you've brewed? I take it, that there is a way of estimating the FG but I've only ever measured it, after the fact.

It will help me make sense of the recipes that get posted here.

Thanks all.

 

[raven19]

It comes down to the attenuation of the yeast selected, and the mash temp.

At around 66 degrees, attenuation should be as per the yeast attenuation provided by the supplier. Dropping the mash temp will increase the attenuation to a certain degree and thus decrease the FG, increasing the mash temp decreases attenuation and increases FG.

It is not an exact science though, grain bills, yeast health, etc., all come into play also.

 

[pimpsqueak]

As with all recipes it's only an estimate based on the assumed fermentability of your sugars and the attenuation of your yeast.
All my brews have come close to the estimated OG and FG but I have never gotten it to match exactly.

Edit: damn. too slow.

 

[big78sam]

+1 to the above

As far as I understand...
If you have an OG of 1060 and the expected attenuation of the yeast you are using is 75%, your OG should be around 1015

In other words 75% of the sugars (or 75% of the 60 points above 1000) are expected to be converted to alcohol and co2 by the yeast
i.e. FG = 1000 + (60 - (60 x 0.75) = 1000 + 60 - 45 = 1015

There are LOTS of other factors but this gives a ballpark figure.