"Jam refers to a product made of whole fruit cut into pieces or crushed, then heated with water and sugar until it reaches "jelling" or "setting" ...
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point, achieved through the action of natural or added pectin, then sealed in containers.
Pectin is mainly D-galacturonic acid connected by α (1–4) glycosidic linkages. The side chains of pectin may contain small amounts of other sugars such as L-fructose, D-glucose, D-mannose, and D-xylose. In jams, pectin thickens the final product via cross-linking of the large polymer chains." - (en.wikipedia.org 03.08.2021)