For my Welch's, I drink it tart. But, you can sweeten. The first thing- DON'T just add extra sugar. It will ferment out and you'll have tart rocket fuel! The thing to do is to make it as the recipe calls for, and let it finish. When it's completely done, then add 2/3 tsp potassium sorbate and 5 campden tablets (for a 5 gallon batch). Rack, and then sweeten to your desired taste. Table sugar is fine. I mix up about 2 cups of sugar in about 3/4 cups water, boil until dissolved and add it to taste. Check the s.g. and wait a week. Check the s.g. again. If it's the same, bottle it.