Fermentable Sugar, e.g. Maple Syrup
I brewed a Maple Stout before Christmas in which I racked the beer to a secondary fermentation vessel where I added 550g of Maple Syrup. I let it sit at 12ºC for 4 days before racking to keg. The schedule was as so:
Day 0, O.G. = 1.067 Day 10, S.G. = 1.015, transfer to secondary, S.G. = ? Day 14, F.G. = 1.017, transfer to keg
I didn't think to take a gravity reading after mixing the beer with the Maple Stout (doh), but even if I did, is that how the ABV would be calculated? Adding the 6.83% of 1.067-1.015 and X% of 1.0xx-1.017. E.g. 1.020-1.017 is 0.39% so 6.83% + 0.39% = 7.22%?
As Christmas was around the corner I just labelled it up as 7.2% and let it be, but for future brews I want to be able to know the exact ABV.
Any sort of sugar or syrup would be the same as whatever method is described for above, but fruit I imagine would be more difficult.
How would one make the calculations if adding fruit? For example, using the same gravity readings above for Day 0 and Day 10 of 1.067 to 1.015, how would you work out the ABV if adding 500g of Mango and 500g Apricot into the secondary fermentation? Or any other fruit for that matter. How do the breweries do it?