Question about FG

**brewd00d** · 10-28-2010, 02:03 AM

Im now officially fermenting my third beer so far!! But as usual, there will still be things im still learning on the way down this thirsty road.

As stated in on the sheet my beer kit came with, the OG i should be at is around 1.044-1.046. When i took the reading before i pitched the yeast i had exactly 1.044.

My questions is, do most beer kits usually give what the FG is supposed to be or is that something that i determine? I was thinking having a known FG would help me out as the fermentation draws near completion. However, this is why usually people check it a couple times per day until the hydrometer reading stays the same, and THATS the FG?

**ChshreCat** · 10-28-2010, 02:14 AM

Yes, on both counts, actually.

Most kits (and most recipes, for that matter) will give a predicted final gravity. Since brewing isn't an exact science, this is a ballpark figure. So, you want to wait until you get a stable gravity reading before considering it done.

Quote:

However, this is why usually people check it a couple times per day until the hydrometer reading stays the same, and THATS the FG?

Couple times a WEEK would be the max. A couple times a day would be insane. It won't change that quickly unless it's right in the height of fermentation, and then there's no reason to take a gravity reading then. I usually check mine once a week and that's it. Some folks check gravity before pitching yeast and then won't check it again for weeks. Several times a day is DEFINITELY overkill.

wetzie · 10-28-2010, 02:18 AM

I have been taking FG readings once a day for three days usually a week after activity stops. I am usually in the fermentor 3-4 weeks. In extracts the OG is pre-determined if you have a successful boil. My OGs have been very close to expected. My LHBS told to take the OG (1.044 ex) last two digits and divide it by 4. Take that number and at it to the end of 1.0 and you will have your expected FG of 1.011. I am not sure how scientific this but has worked out pretty well so far.
Good Luck

**brewd00d** · 10-28-2010, 04:19 PM

Quote:

Originally Posted by wetzie

I have been taking FG readings once a day for three days usually a week after activity stops. I am usually in the fermentor 3-4 weeks. In extracts the OG is pre-determined if you have a successful boil. My OGs have been very close to expected. My LHBS told to take the OG (1.044 ex) last two digits and divide it by 4. Take that number and at it to the end of 1.0 and you will have your expected FG of 1.011. I am not sure how scientific this but has worked out pretty well so far.
Good Luck

silly me, i meant per week. the kit i got didnt give a "predicted" final grav so i guess ill have to check it when and see when it starts to stabilize.

Frodo · 10-28-2010, 04:26 PM

Quote:

Originally Posted by wetzie

My LHBS told to take the OG (1.044 ex) last two digits and divide it by 4. Take that number and at it to the end of 1.0 and you will have your expected FG of 1.011.

That's pretty simplified but it'd get you in the ballpark. The attenuation of the yeast will factor in there too.

**ChshreCat** · 10-28-2010, 04:31 PM

Quote:

Originally Posted by Frodo

That's pretty simplified but it'd get you in the ballpark. The attenuation of the yeast will factor in there too.

Attenuation of the yeast, temp of mash (if doing a PM or All-grain brew) among other things. You really have to just let the beer ferment out and give it time to make sure it's done. Estimating the FG is still good because if you stabilize at 1.016 and your predicted FG was 1.010, then you need to go back and see if there's a reason for it to finish there or if you just have a stuck ferment.

On the flipside, you can't say "It's hit the FG, time to bottle" because it could go past it. It's just an estimate.

wetzie · 10-28-2010, 07:29 PM

Good point on that it is expected. I missed a FG that was supposed to be 1.015 and mine was 1.020 after four weeks and three consistant readings. Should I have tried to restart it or was it ready. The beer was an extract Porter.

Frodo · 10-28-2010, 07:39 PM

Quote:

Originally Posted by wetzie

Good point on that it is expected. I missed a FG that was supposed to be 1.015 and mine was 1.020 after four weeks and three consistant readings. Should I have tried to restart it or was it ready. The beer was an extract Porter.

Seems like it's pretty common for extract batches to finish a bit higher than expected, FG of 1.020 seems a pretty common theme for extract.

**ChshreCat** · 10-28-2010, 08:03 PM

Yeah, I'd have gently roused it and given it another week just to make sure, but some of my extract heavy PM batches will finish high like that.

**nilo** · 10-28-2010, 08:26 PM

You will find that trying to predict FG with a higher precision is necessary when you want to brew to style, when you add unfermentables like crystal malts, carapills or lactose or mash at specify temperatures.
If you are just brewing a known recipe and needs to determine if it is done fermenting, just take gravity readings.