Predicting your Final Gravity(FG) reading

Hello all, newb here. I am the repetitive story of SWMBO buys Mr. Beer for me as Christmas '08 Gift and here I am completely enraptured by the hobby already. I brewed my first batch on 2/7/09, and just brewed batches 2 and 3 on 2/21/09. I haven't even had my own first HB yet. How's that for patience!!!

My question is this, can you predict or plan what the target FG hydrometer reading should wind up being?

I have read alot about possible stalled fermentation at 1.020 or so and that led to moving from fermentation to bottling too quickly. I just brewed 2 Mr. Beer recipes, May The Schwarz Bier With You, and Amercian Gold Premium ( with some much advised modifications, i.e., DME instead of Booster).

My OG hydrometer readings were: 1.058 for Schwarz Bier and 1.050 for the American Gold.
My first Brew (Canadian Draft) finished finished at (FG) of 1.008+. After starting around 1.029 (OG).

When I take my first readings in a couple of weeks on batches 2 and 3, can I predict or expect a certain reading? How can I find that out? I am only concerned about knowing the difference between a stall and really being done. In the mean time, I will relax, smell the fermenter bin, and have my commercial beer while I wait.

Yes it is possible. When you are doing extracts, it is easy to get very close. All you need is to know a little about your yeast, specifically is apparent attenuation. This is generally show as a percent (ie 75%). You then know your OG and how much it will ferment, leaving you to solve for the predicted FG.

For example if you had a beer that had a OG of 1.050 and the yeast had an average attenuation of 80%, you would expect the FG to be approx 1.010

Just remember that SG depends on volume. Saying that you can predict OG depends on what your final volume is. You can boil an 8 gallon wort with one SG down to a 5 gallon with with a much higher SG. Then, the FG depends on the OG and what the yeast does with the fermentables in there. There are a lot of things going on there.


TL

Parker36 said:

Yes it is possible. When you are doing extracts, it is easy to get very close. All you need is to know a little about your yeast, specifically is apparent attenuation. This is generally show as a percent (ie 75%). You then know your OG and how much it will ferment, leaving you to solve for the predicted FG.

For example if you had a beer that had a OG of 1.050 and the yeast had an average attenuation of 80%, you would expect the FG to be approx 1.010

Click to expand...

OK, so in the case of the American Gold Premium, I used Danstar Nottingham yeast (instead of the Mr. Beer no name yeast). Their technical data doesn't quote an attenuation, just that it is High Attenuation with final near 1.008. But doesn't that depend on other factors in the extract, like hops?
Anyone know the expected attenuation for Nottingham yeast?

Is the equation, OG x Attenuation percent = FG ..... or
(((1 - OG) x Attentuation percent ) + 1 ) = FG?

TexLaw said:

Just remember that SG depends on volume. Saying that you can predict OG depends on what your final volume is. You can boil an 8 gallon wort with one SG down to a 5 gallon with with a much higher SG. Then, the FG depends on the OG and what the yeast does with the fermentables in there. There are a lot of things going on there.


TL

Click to expand...

In my case, these are Mr. Beer recipes, not 5 Gal brewing. I don't have a boil down factor, just 2.2 Gals of water/prehopped LME/DME/Hops.

Using the yeast strain's attenuation rating is not a reliable way to predict the FG because that will depend on the yeast and the fermentability of the wort. Since the Mr. Beer recipes are extract based the kit should be able to specify the FG that you can expect.

Kai

Kaiser said:

Using the yeast strain's attenuation rating is not a reliable way to predict the FG because that will depend on the yeast and the fermentability of the wort. Since the Mr. Beer recipes are extract based the kit should be able to specify the FG that you can expect.

Kai

Click to expand...

I couldn't seem to find the target FG quoted anywhere. It's not a kit per se, but a Mr. Beer Recipe. I bought the additional ingredients after having been given a refill pack, so there was no where to get the FG as far as I could find. Couldn't find it on the web-site for it either.

If your SG is the same over 3 consecutive days it should be ok to bottle. If your SG is suspiciously high (OG=1040 and FG?=1020) I would consider why (figure how much fermentibles you are using and compare to other extract recipes?) to see if maybe it's stalled. Others here with more experience can elaborate for you but I wouldn;t worry much about it. Beer seems to be pretty hard to mess up.

Parker36 said:

Yes it is possible. When you are doing extracts, it is easy to get very close. All you need is to know a little about your yeast, specifically is apparent attenuation. This is generally show as a percent (ie 75%). You then know your OG and how much it will ferment, leaving you to solve for the predicted FG.

For example if you had a beer that had a OG of 1.050 and the yeast had an average attenuation of 80%, you would expect the FG to be approx 1.010

Click to expand...

That's a good rule of thumb.

Just keep in mind that even that's likely to be off, because different worts have very different fermentabilities. If you're doing a Belgian with a lot of sugars in it, it'll ferment a lot more with the same yeast than something that's got no simple sugars and less fermentable grains.

Basically, the yeast will finish where it finishes.