I've been experimenting with adding spices and sugar to my rums. The problem I'm running into is that after I add the sugar (simple syrup or cane spirit caramel) the ABV reading on my alcohol hydrometer drops significantly. Obviously the small amount of water in the syrup would lower the ABV, and I've read that sugar lowers the ABV as well, but I don't think by the amount I'm reading on my hydrometer. My question is, how do you determine the correct ABV of the rum after back sweetening? What are the alternatives to using a hydrometer?