My girlfriend and I have been experimenting with making different flavors of chocolate truffles. One difficulty with this is that different flavorings have different amounts of sugar, meaning we need to adjust the amount of other sweetening in the truffle to keep it from being overly sweet or bitter (usually by changing the ratio of unsweetened to semisweet chocolate). Obviously getting the sweetness exactly right is going to take some experimentation, but we'd like to be able to start by making the total amount of sugar in each truffle the same, no matter what flavor it is.
We can figure out approximately how sweet most flavorings are are by using their "Nutrition Facts" labels. Unfortunately, alcoholic drinks don't come with these labels, which means we need a different strategy for liqueur-flavored truffles. Neither of us drinks very much alcohol, so we don't have a very good intuition for which potential flavors might be sweeter. Googling gives several sites with widely varying numbers, and I don't know which ones to trust. For example, this site claims an ounce of Kahlua has 11.2 g of sugar, while this site claims it's 15 g.
Is there a good way to determine how much sugar is in a given liqueur? Ideally, I would like either a pointer to a reliable source, or a simple experiment I could do myself to determine sugar content.