is it possible to calculate expected final gravity?

[je52rm]

I have an ESB that had an OG of 1.071-1.072 and i used WhiteLabs WLP013 london ale yeast. 17 days later and its holding at 1.015 (for the last three days). The WLP013 is supposed to have 67%-75% attenuation. Is this what i would use to calculate what my expected final gravity will be? If so how can I do that? Thanks!

 

[hopheaded]

If its holding there it might be done fermenting, but you can use beer calculus online (by hopville) to get their estimate on expected fg, given the recipe you input.

 

[Yooper]

It's simple math. If you figure 67% of 71, and 75% of 71, you can expect that your FG will fall between the two figures.

So, for an OG of 1.071, you can expect a FG of between 1.022 (67.5%) and 1.017 (75%). Since you are below that at 1.015, you got an attenuation of 77.7%.

An "average" attenuation is just that. You can plan on it being higher or lower depending on yeast strain, ingredients, and the size of the starter.

 

[jonmohno]

Another reason you can calculate it,but cant always expect it.

 

[je52rm]

It's simple math. If you figure 67% of 71, and 75% of 71, you can expect that your FG will fall between the two figures.

So, for an OG of 1.071, you can expect a FG of between 1.022 (67.5%) and 1.017 (75%). Since you are below that at 1.015, you got an attenuation of 77.7%.

An "average" attenuation is just that. You can plan on it being higher or lower depending on yeast strain, ingredients, and the size of the starter.

Ok cool so is it safe to assume that once you reach full attenuation from the specific yeast strain used that you shouldn't really expect much more from it (under normal circumstances)?

 

[neomantra]

Apparently your mash temperature affects this too, which I think that helps explain why there is a range as opposed to a specific number. In general I find most brewing software really stinks at doing this correctly. In particular if you do all-grain brewing I find my FG is almost always lower than the software predicts.

If you're just trying to figure out if it's "done" then your best bet is to 1) wait until the krausen disappears and then 2) take hydrometer measurements every 3-4 days to ensure your FG is not decreasing any more. Sometimes you hear people say to check more frequently but I find that if you take a new reading on a daily basis then sometimes it's hard to tell if it's still dropping further or not.

 

[Ryush806]

Ok cool so is it safe to assume that once you reach full attenuation from the specific yeast strain used that you shouldn't really expect much more from it (under normal circumstances)?

Correct. However if you're really interested in the fermentability of your wort you can do a forced fermentation test. Basically you pull of a sample of your wort, over-pitch it, and ferment above 80 F for a few days. Then you check the gravity. That gravity is the lowest you can expect your beer to go. If your beer makes it there, it's definitely done. If it gets real close and stops moving you know you had a good fermentation that didn't get stuck.