Original Gravity and sugar levels

[AussieLondon84]

I got 1052 OG from my ginger beer using 3 kilograms (6.6 pounds) inverted using lemon juice.
So, I know ginger has no fermentable sugars, so could I potentially wait 3 days, then make a sugar syrup with 2 kilograms more sugar from boiling to reduce to a liquidy syrup, and add it to the fermenter (uses champagne yeast)?

Also, how would I work out FG when I am adding in more sugar part way through fermentation?

Less importantly, but thought I should mention, I am also partly curious if molasses (I didn't use much will be treated as a sugar for the hyrdo reading, aka, increasing liquid density)?

 

[clibit]

I don't see why you couldn't add more sugar during fermentation. It's a valid technique in making strong beers, to enable the yeast to multiply in a weaker wort.

You's work out final gravity in the same way, with a hydrometer. To work out what the sugar adds to the gravity, you could take hydrometer readings before and after the addition. Or work it out using brewing software.

Molasses are a form of sugar.

 

[AussieLondon84]

I don't see why you couldn't add more sugar during fermentation. It's a valid technique in making strong beers, to enable the yeast to multiply in a weaker wort.

You's work out final gravity in the same way, with a hydrometer. To work out what the sugar adds to the gravity, you could take hydrometer readings before and after the addition. Or work it out using brewing software.

Molasses are a form of sugar.

Thanks for the advice mate.
I will do exactly that, I want to try to get to 15% if I can and lightly carb it as a sort of ginger sparkling wine, I am estimating this will need 6 kilos of sugar though, as 3 kilos only got me 1052 which can only yield maximum 5.2% I think.
So adding an extra 6 kilos of sugar (added to the original 3kg at pitching, to make 9kg total) should get to 15% (unless my calculations are mistaken)?