calculating abv

[ebbz]

Is it a good idea or even feasable to take a specific gravity reading after the bottles have conditioned for a while after it goes a little flat to get better FG?

[John Sand]

You can. You can let it sit and warm to remove the carbonation, or pour it back and forth between glasses, or shake it in a bigger container. Once it is flat you can take the final gravity.

[Pudge]

Eh, no real need as long as you took a reading prior to bottling. Minimal change at best. Enjoy the beer and think about your next brew session instead

[RickBeer]

For what purpose?

[ScrewyBrewer]

Is it a good idea or even feasable to take a specific gravity reading after the bottles have conditioned for a while after it goes a little flat to get better FG?

The term FG, or Final Gravity, is just that, the 'final' gravity that the beer will ever reach. The best thing to do, when bottle priming your beer, is to only bottle it after the beer has fermented out completely.

Hydrometer readings, taken over the course of two days, that show no change in gravity, indicate the the fermentation has completed. At this point adding priming sugar, capping and carbonating the beer at room temperature will produce the best results.

[Kealia]

IIRC, the addition of priming sugar added something minimal like 0.01% or 0.10% to the final product.
So taking the reading at the time of bottling/kegging gets you the number within a minimal difference.

[ebbz]

Thanks for the replies, all. I was just looking for a more accurate ABV. I thought I remembered reading that the priming sugar can add as much as a half a percent to the final product. Sounds like an experiment in the works.

[RickBeer]

Nope. Maybe 0.1%.

[bpgreen]

I've seen estimates varying from .01% to .5%.

If you dissolve the sugar in some volume of water for batch priming, it also changes things.

If I had more time and energy, I could calculate the effect of priming sugar, but it has never meant enough to me to try to figure it out.

RDWHAHB.

[Pudge]

If you really want to know, I'd say just don't cap the last bottle. Cover it with a piece of aluminum foil and let it sit at room temp for a few days. The priming sugar should ferment out very quick and most of the CO2 will simply dissipate.

[ebbz]

If you really want to know, I'd say just don't cap the last bottle. Cover it with a piece of aluminum foil and let it sit at room temp for a few days. The priming sugar should ferment out very quick and most of the CO2 will simply dissipate.

That is a great idea, thanks. Being part scientist, that should quell my inner curiosity. I was mostly just interested in the experiment more so than being able to adding a higher ABV to the label.

[RickBeer]

You can do the same thing with any receipe planner, such as QBrew. I in fact did this some years ago because I was curious.

Example:

I have a recipe in there now which returns an OG of 1.59 and an FG of 1.015, for an ABV of 5.7% for 5 gallons, which is 640 ounces. I then change it to 644 ounces, accounting for 4 ounces of water, so I put in 5.03 gallons (won't let me put in .00125). No change in anything. Now, I put in cane sugar, I would use say 130 grams or .2866 pounds, so I put in .287. Recipe now reads OG of 1.061, FG of 1.015, and an ABV of 5.9%. So in short you will add perhaps 0.1 to 0.2 to the ABV.

[ebbz]

So, did you assume a FG of 1.015 after the priming sugar fermented because that is what was read after the primary finished or did you take another SG reading afterwards?

[RickBeer]

That's what the program shows, it assumes a final gravity. Adding that small amount of sugar should not affect FG, it will affect OG, and that's where the tiny uptick in ABV comes from.

I've never measured my beer in the bottle with a hydrometer. My reason to measure ABV is solely so I know if I have a session beer, a normal beer, or a "watch out" beer.

[mashani]

So, did you assume a FG of 1.015 after the priming sugar fermented because that is what was read after the primary finished or did you take another SG reading afterwards?

So ebbz... the trick here is that sugar will ferment out 100%, where say if you were to prime with malt (IE to keep it Reinheitsgebot) might ferment out 70% to 80%.

So both will increase your effective OG (the amount of sugar your batch has as a total) if you add it late into the fermentation.

But only extra malt will affect your final gravity, because some of it will not ferment out. So if you were to prime with malt it will actually possibly increase your FG ever so slightly. Whether you notice or not, probably not. But you still can't really calculate the ABV from the FG.

Both will increase the ABV, but you can't calculate it by checking your FG a second time after you add that little bit of sugar... the FG will remain pretty much the same after it ferments out. Because it ferments out 100%. So in either case, you have to calculate it by increasing your OG and then comparing it to the FG.

So the only way to really "guess" is to slightly increase your OG by how much sugar you added, IE add 5oz of sugar or whatever to your brewing software as if it was part of your batch.

Why anyone really would want to bother with that, I don't know, but that's how you can do it.