My main worry is if it does have sugar, that it will be a little tricky to calculate the carbonation level and how much more sugar you'll need to reach appropriate levels. Most extracts I've seen are pretty well sugar free, which for this, is a good thing.
The label should list the amount of sugar (if any) per serving ... Should be straight forward to figure out the total amount of sugar in the the amount of extract you want to use, then deduct that amount from your priming sugar...
The label should list the amount of sugar (if any) per serving ... Should be straight forward to figure out the total amount of sugar in the the amount of extract you want to use, then deduct that amount from your priming sugar...
Then again, I'm probably overthinking this, as the change in volume would be negligible from extract. At first I had been thinking about using juice to carbonate, which can make things a little more tricky.