It’s often the kind of confection the French call a “pâte de fruits”. These are more tart and more firmly gelled than a jelly you’d spread on toast. The gelling agent is pectin, a protein extracted from fruit, not gelatin (pâte de fruits recipes for home cooks often use gelatine because it’s easier, but the pros always use pectin). The pectin gives it its characteristic mouth feel. The tartness usually comes from added citric acid.
Here’s a typical recipe (makes one hell of a lot of pâte de fruits):
1000 g raspberry puree
1140 g sugar
200 g corn syrup
15 g citric acid diluted in 15 g. water (or 15 g. lemon juice)
20 g powdered pectin
–>Mix about 100 g. of sugar with the pectin. Whisk them together really well.
–>Heat the puree to 120 degrees. F.
–>Add the pectin/sugar mixture while whisking vigorously. Bring to a boil and let boil one minute.
–>Add the corn syrup and the rest of the sugar. Cook to 223 degrees, F.
–>Stir in the citric acid/water mixture or the lemon juice. Cook one more minute.