Bottle Conditioning and ABV

[Brews and Blues]

I know there are a lot of variables, but what effect if any does bottle conditioning have on the beer's ABV?
To make a long story short, the ABV of my cream ale came out slightly lower than expected. I believe I know the reasons why, so I don't need to delve into that. But, will the specific gravity of the beer be lower after 2 weeks in the bottle with the priming sugar? I have read that the reason the FG is taken BEFORE bottle conditioning is because the hydrometer can give mixed reading after the beer is carbonated. But, I have been using a refractometer, so can i take a FG of carbonated beer with that to find the exact ABV?

 

[bucketnative]

Typically, bottle conditioning will increase the ABV. You end up adding approximately 1 gp (0.001 sg) for each 0.5 vol of CO2. This usually ends up being about 4 gp (0.004 sg) added, and all of that will be converted to alcohol and CO2 during conditioning. Using the rule of thumb that ABV = (OG-FG) * 131, you can see that the ABV will go up by about 0.5 % ABV.

Refractometers, are nice, but I think that many people around here will tell you that the absolute measure will be a hydrometer. @balrog posted some data the other day, where he basically shows that, even with the correction factors, the refractometer to hydrometer relationship was not perfect.

Measure your SG prior to adding priming sugar to determine you pre-bottling ABV. Then you can determine the increase in gravity caused by adding sugar. Assume that will ferment 100 %, and you will have an estimation of your ABV.

 

[Brews and Blues]

Typically, bottle conditioning will increase the ABV. You end up adding approximately 1 gp (0.001 sg) for each 0.5 vol of CO2. This usually ends up being about 4 gp (0.004 sg) added, and all of that will be converted to alcohol and CO2 during conditioning. Using the rule of thumb that ABV = (OG-FG) * 131, you can see that the ABV will go up by about 0.5 % ABV.

Refractometers, are nice, but I think that many people around here will tell you that the absolute measure will be a hydrometer. @balrog posted some data the other day, where he basically shows that, even with the correction factors, the refractometer to hydrometer relationship was not perfect.

Measure your SG prior to adding priming sugar to determine you pre-bottling ABV. Then you can determine the increase in gravity caused by adding sugar. Assume that will ferment 100 %, and you will have an estimation of your ABV.

Thanks! I actually had someone on this board recommend the refractometer. I loved it for how little beer that I needed for the measurement. Hopefully it is somewhat accurate.
If I'm thinking about this correctly, it really shouldn't matter what I use or if the refractometer is a little off, as long as I am consistent. If the refractometer reading is x amount higher than the hydrometer reading on the OG, then it should be x amount higher on the FG as well. So the difference between the two will be the same if I use a hydrometer, making the ABV formula come out the same.

 

[balrog]

Not necessarily by same % since the two tools are measuring different things -- one measuring density, the other is measuring index of light refraction through liquid. Basically you have to make up known samples to see what the differences are, and as that is *WAY* more than this lazy brewer wants to do, I just measure SG with two different hydrometers (occasionally tested for 1.000 with water) and consider them to be correct.

 

[bucketnative]

If I'm thinking about this correctly, it really shouldn't matter what I use or if the refractometer is a little off, as long as I am consistent. If the refractometer reading is x amount higher than the hydrometer reading on the OG, then it should be x amount higher on the FG as well. So the difference between the two will be the same if I use a hydrometer, making the ABV formula come out the same.

No, that is not correct. The refractometer is intended to be used on solutions of sugar in water (fruit juice or wort). The refractometer should be accurate for unfermented wort.

Once you get alcohol in the mix, it has an effect on the refractive index of the solution. The refractometer will not read accurately once fermentation has started. There are correction calculators for this on the web, but the data that I saw yesterday suggested that the relationship between refractometer and hydrometer is not necessarily linear... meaning that there are things other than alcohol that may affect the refractive index of the beer. See @balrog chart here: https://www.homebrewtalk.com/forum/threads/first-time-this-has-happened.674492/#post-8769253

 

[balrog]

Be careful with that data; I'm no certified National Bureau of Standards. I've been know to take measurements while drinking.

 

[Brews and Blues]

No, that is not correct. The refractometer is intended to be used on solutions of sugar in water (fruit juice or wort). The refractometer should be accurate for unfermented wort.

Once you get alcohol in the mix, it has an effect on the refractive index of the solution. The refractometer will not read accurately once fermentation has started. There are correction calculators for this on the web, but the data that I saw yesterday suggested that the relationship between refractometer and hydrometer is not necessarily linear... meaning that there are things other than alcohol that may affect the refractive index of the beer. See @balrog chart here: https://www.homebrewtalk.com/forum/threads/first-time-this-has-happened.674492/#post-8769253

Well then maybe my ABV isn't low at all. I guess I will have no idea since I have used a refractometer. I can probably check the FG with a hydrometer now and hope the carbonation doesn't mess with it too badly.

 

[bucketnative]

Well then maybe my ABV isn't low at all. I guess I will have no idea since I have used a refractometer. I can probably check the FG with a hydrometer now and hope the carbonation doesn't mess with it too badly.

Shake your sample and let the CO2 come out of solution as the beer warms up. Do that until the sample is flat, then measure.