I know this is very old, but for anyone who uses the forums like I do for research purposes - I just wanted to correct some of the misinformation above (no offense intended). Pectin is pH dependent, as mentioned above, but the high acid (low pH) is what sets the gel. Depending on the type of pectin used, pH range is around 3.2-3.5. Not setting? Try increasing your acid (or your pectin, or your solids, or some combination thereof).