The directions say to carbonate only water, and then add flavorings to it. I've always used it that way. I typically fill the remainder of the jug up with fruit juice (say, cranberry or cherry cider, something tart), AFTER I have carbonated the water. (However, I don't know why you couldn't just carbonate other things directly, such as apple cider -- to make sparkling apple cider.) I presume they don't recommend it because of the cleaning issue. The apple cider would get on (and perhaps up inside?) the CO2 spout, where it would be hard to clean. ??? Perhaps there is a health issue there. I don't know. Other than that possibility, I cannot think of any reason why it wouldn't work excellently.