Jam is simply a cooked mixture of fruit and sugar. It is distinct from what we in America call jelly, since jelly is a thickened mixture of sugar and fruit juice only. Most jams start out as a roughly 50-50 mixture of sugar and fruit by weight. By the time they’re cooked, however, that proportion changes to roughly 65% sugar. Some food cynics out there question whether jams really have to be that sweet, and the answer is yes, they do, at least if they’re going to have any sort of shelf life in the pantry. Slightly less sugary versions of some preserves have been developed over recent years that are still safe for eating. When I find such a recipe I like to use it since though the preserve is still very sweet tasting, it lets more real fruit flavor shine through.