Finding OG from FG? or FG to low.

I just made a IPA and with an estimated efficiency of 60% (since that is what I usually get not sure how to improve it) I should have a OG of 1.076 and a FG of 1.021. The problem is I just measured the FG and it was 1.012.

Now my main concern is that means my efficiency is only 40%. I did not have a hydrometer at the time I made this so I didn't get an accurate OG is there a way to back calculate OG from FG.

Here is the recipe http://hopville.com/recipe/1280963/american-ipa-recipes/ipa-test and here is my procedure.

I heated up 2 gallons of water to 170 degrees and poured it into my mash tun (a plastic 5 gallon bucket) and waited till it cooled down to 165 and then added the grains (all double milled 6lbs of 2-row, 11oz of special B, and 6oz of Crystal 60L). The temp dropped to 150-152 (lower then I wanted) so I lidded up the bucket and wrapped two towels around it to insulate it. 30 min later it had dropped to 145 so I heated up another quart of water to 165 added it in and raised it back up to 150-152 or so. Mashed for another 40 min. I then heated up a gallon of sparge water to 170 and sparged the grains to make 3 gallons total. I boiled this and added the hops as normal and ended up with about 1.9 gallons what i was shooting for since I was only doing a 2 gallon batch.

Now I was really shooting for a good Double IPA of about 7.5%ABV but this FG reading of only 1.012 means I might possibly have a much lower beer. So is it possible for the yeast I used (US-05) to have gone nuts and consumed that much sugar dropping my FG that low or is it more likely my efficiency is super low like 40% like I fear? Would the lower mash temps mean that I released a lot of fermentables so it just finished dry and I do have a much stronger beer of 8.4% (as per brewers friend ABV calculator based on the projected OG from Hopville) Since I didn't have a hydro at the time I finished making this I do not know what the OG was, I know that is a valuable piece of info and on my last few beers I have been using it so I know my OG and FG.

Thanks for you help.

It could very well be that the low mash temps gave you more fermentables than the recipe is designed for, hence the lower FG...there is really no way to back calculate because of the variables

You seem to have the math wrong.

With an OG of 1.071 and a FG of 1.012 you get a 7.7% ABV.

The lower the FG in relation to the OG the highher the ABV. The formula is ( OG- FG) X 131.25.

If your mash temp was low then you get a lower FG. US-05 does attenuate well so without actually having your OG you could have a 7.7 ish brew.

beergolf said:

You seem to have the math wrong.

With an OG of 1.071 and a FG of 1.012 you get a 7.7% ABV.

The lower the FG in relation to the OG the highher the ABV. The formula is ( OG- FG) X 131.25.

If your mash temp was low then you get a lower FG. US-05 does attenuate well so without actually having your OG you could have a 7.7 ish brew.

Click to expand...

Or it could mean his OG was only about 1.050...With AG the efficiency variable makes it near impossible to back calculate....it would be straight forward with extract and a known volume

Thanks for the help.
Beer golf the only problem is I don't know if my OG is 1.071 using hopville the only way I could get a FG of 1.012 is to have a OG of 1.051 or close to it. I am assuming the program on that website is designed on a average attenuation of the selected yeast so on average a FG of what I got should mean I have an OG of what they predict. Does this sound right? Thanks.

Yes, the OG is pretty close to 4X the OG unless there are corn sugar or other adjuncts to consider.

Hopville is wrong with projecting your probable FG. FG is far more than a function of a percentage of OG. It's a combination of ingredients, mash temperature, yeast strain, yeast health and so on.

You can easily get a FG of 1.012 with 1.071 for an OG, or 1.050 for that matter. You simply can't extrapolate backwards from the FG to guess an OG. The only way to know your OG is to measure it before fermentation starts.

Thanks guys that helps a ton. I guess I will find out when I drink it in a few weeks if it taste like 7.7 or less no big deal if it is off just wanted to know my efficiency more then any thing else.

I just got Beersmith 2 and they said that the estimated FG would be 1.013 so at 1.012 I am pretty darn close I will probably defer to Beersmith from now on.

Ply318ci said:

I just got Beersmith 2 and they said that the estimated FG would be 1.013 so at 1.012 I am pretty darn close I will probably defer to Beersmith from now on.

Click to expand...

It's a good program, but I've noticed that they tend to just give you an average attenuation and not a probable FG.

For example, if you have 8 pounds of grain, 2 pounds of corn sugar, and mash at 149 and use nottingham yeast, I would expect a FG of something like 1.005 or so. If you have 8 pounds of two row, and 2 pounds of crystal and mash at 158, even using the same yest, I would expect a FG of something more like 1.018-1.020. Add a pound of lactose, and I'd expect 1.027.

But Beersmith might give you the same projected FG of of 1.010 for all of those examples, if the OG is 1.045. Which is incorrect, of course. I don't think any good software actually predicts FG accurately. It comes more from experience and knowledge of fermentability of ingredients. I wouldn't rely on predicted FG from ANY software.

You can determine your OG after fermentation if you take both a refractometer and a hydrometer reading. Then just punch them into this calculator:
http://www.brewheads.com/refract-getog.php

This is most commonly used to find the OG of a commercial brew for cloning purposes, but it will work here as well.

The physics behind it are a bit hazy to me, but the basic idea is that the hydrometer measures density only, while the refractometer measures the index of refraction (n) of the liquid. 'n' is a function of both density AND alcohol content. With density known (from the hydrometer) %alcohol can be found with the refractometer measurement. With % alcohol and hydrometer FG, you can back-track to OG.

Ok so I bottled this tonight and I tasted a uncarbed sample and it tasted like around 8.4% alcohol this is based on a estimated OG of 1.076 and a measured FG of 1.012. I believe that my mashing around 148 must have released a ton of fermentable sugar and I used a almost a full package of US-05 so I think the yeast went nuts. Now my question is this uncarbed sample was sweet very sweet and almost no hop aroma or flavor or real bitterness I used .75oz of chinook .75oz of centennial and 1.75oz of simcoe. I used the chinook as the main bittering at 45 min (I screwed up my timing and did a full hour boil but didn't add the hops till the 45 min mark) and then from the 30 min mark till flame out I added the centennial and the simcoe in a continuous hopping method adding about .1oz of the centennial every five min and .2oz of the simcoe every five min (or about that much since I had some left over). Now I was going to dry hop with the rest of the hops about .2oz of centennial and .4oz of simcoe but used them for another brew. Now will my beer get more hoppy in flavor aroma and bitterness or did i screw up by having to much crystal and special b (5% and 10%) or am i tasting the bottling sugar (48 grams dissolved over heat in .5 cup of water) Will this flavor change over time as it is now it taste more like a barley wine then a IPA which is fine i just want to know where i went wrong so that next time i can make a IPA Also this is only a 1.8 gallon batch thanks.

Any ideas at all thanks.