I rarely use commercial pectin in my jams, relying instead on the natural pectin of the fruit (plus I like a looser set). But there are times when a little boost is helpful if I’m preserving low-pectin fruits, making a larger batch, or wanting to reduce cooking time. That’s when I reach for my perpetual stash of lemon seeds. Lemons and other citrus fruits are rich in pectin, which thickens jams.