Measuring ABV after bottling

[Dennis]

Let me preface this by saying, I did measure my gravity OG and FG, but am concerned these measurements were off.

About 3 weeks ago I brewed what was supposed to be an Imperial IPA. I did a back to back brew. My intent was to brew both 5 gal batches in my small mashtun which has a rather high 80% efficiency. But after the first batch took an incredible amount of time to fly sparge, I decided I would use my larger MLT which has a lower efficiency.

The details, measured OG: 15 brix, FG 9.5-10 Brix. Around 5%

5 gal batch
69% - 11lbs - OiO Pale Malt
19% - 3lbs - Simpsons Maris Otter
6% - 1 lb - Carapils
12 oz - Pale Belgian Candy Sugar - 30min of boil
2% - Caramel Malts 60L

Mashed with most of the water needed and fly sparged the last 2 gal to rinse grains and get my boil vol.

90min boil. pH was fine. I only used my refractometer and it showed 15brix.

Fermented with 2L starter of WLP001.

So I the beer has carb'd up and just trying a sample and I can say it is boozy. Not that it tastes boozy, but I got half way through a bottle and I got an Imperial Stout sized buzz. Very warming. There's no way this beer is 5%. Based on the typical attenuation of WLP001, this would tell me the beer is closer to 1.080 OG

Does anyone have a method of measuring the ABV after the beer has been bottled, giving you have the FG?

Thanks

 

[Tombstone0]

You can measure your FG after bottling just make sure to get as much co2 out of suspension as possible before taking the measurement.
Did you use your refractometer to take your final gravity? If so you need to correct the measurement. Alcohol throws off the measurements made by a refractometer. There are calculators to correct for it online and in most brewing software

 

[Yooper]

Does anyone have a method of measuring the ABV after the beer has been bottled, giving you have the FG?

Thanks

If you plug the OG and FG into correction software, that should get your close. Remember that refractometers read the refraction of light in a sugar solution, and alcohol skews the reading, so a reading after fermentation starts will always be incorrect.

If you use the correction software, it's not 100% accurate, but it's often close enough: http://seanterrill.com/2012/01/06/refractometer-calculator/

The best way to determine your ABV is to use a hydrometer at bottling. Without a hydrometer reading, a refractometer reading will give a guess.

in your case, I would say that your OG reading is way off, though. That amount of grain seems like if you had a decent efficiency you would be much higher than 15 brix.

 

[Dennis]

Yeah, I've used the correction tools. I know the refractometer reading isn't exact after fermentation, but when bottling, the sample I took was from the last bit of the fermenter and was full of hop crud. So I let it settle out and just used the refractometer. The FG is not my concern. As you say, my OG is probably way off. I gathered that much.

I'm trying to find a way to determine the OG or ABV when all you have is the FG. I know it's probably a lost cause and it's really the first time I've had this problem.