Working out ABV with multiple sugar additions

I really suck at this maths stuff (I normally just get ballpark figures using online calculators), so can someone help here?

Making this year's batch of ginger wine (about 20L). I used about half actual white grape must this time, bought from the local vineyards for a bargain price, rather than using raisins or whatever - figured it CAN'T do any harm! The rest of the bill is sugar. But my calculations are off because of this little experiment - I have gone from 1082 OG all the way to dry, or as near 1000 as makes no odds, which I didn't think would happen. Fermentation is still going strong, so I am happy to keep adding sugar until the yeasties give up, not bothered about a high ABV, and if I go overboard a bit with the sugar it doesn't matter as I plan to "backsweeten" anyway.

But how do I work out my ABV from multiple additions of sugar like this?

E.g. I have gone from

1082 -> 1000

I then add, say 1kg of sugar to take it back up to around 1012. Then, (for example), it ferments back down to 1002 (or maybe it ferments dry again and I add MORE sugar).

How do I work out ABV from that, and is it even possible without getting a bit more involved with the volume, specific gravity of water/sugar etc?

I wouldn't even care that much about ABV, but I part of the batch is for friends, and they will want to know what they are drinking

Tell them its 14.5%. They will never know otherwise.

The math is pretty straight forward.

Sugar adds 46 points per pound per gallon. If we convert to your vastly superior metric units, that's:
(3.78541 L/gal) => 46 * 3.78541 = 174.13 points per pound per liter, and then
(20L batch) => 174.13 / 20 = 8.71 points per pound per 20L, and then
(2.20462 lb/kilo) => 8.71 * 2.20462 = 19.19 points per kilo per 20L.

So, for every kilo of sugar you add, figure you can add ~19 points to your effective starting gravity. Then, figure out your final gravity, and calculate your ABV by whatever formula you usually use.

MalFet said:

The math is pretty straight forward.

Sugar adds 46 points per pound per gallon. If we convert to your vastly superior metric units, that's:
(3.78541 L/gal) => 46 * 3.78541 = 174.13 points per pound per liter, and then
(20L batch) => 174.13 / 20 = 8.71 points per pound per 20L, and then
(2.20462 lb/kilo) => 8.71 * 2.20462 = 19.19 points per kilo per 20L.

So, for every kilo of sugar you add, figure you can add ~19 points to your effective starting gravity. Then, figure out your final gravity, and calculate your ABV by whatever formula you usually use.

Click to expand...

THANKS! OK, so there was a bit of math(s), especially due to my reckless use of metric units . But that makes sense - I guess my main problem is I don't have an exact volume measurement, but I'll guesstimate, like I said, a ballpark figure is fine. Your calculation tallies with the hydrometer - I added 1kg sugar, and although it is hard to get it all dissolved, the hydro is indeed showing about 1.016-1.018, presumably another 0.002 can be added for undissolved sugar, and that's perfect - thanks!

(I still hate maths though... My mind just goes a blank when I see any kind of formulas!)