Wine contains very little natural pectin, the substance responsible for making jam set. A wine-based jam made with regular granulated sugar and no added pectin will remain liquid no matter how long it is boiled. The solution is to use jam sugar (which contains added pectin) or to stir in liquid pectin after dissolving the sugar. Lemon juice also assists setting by releasing natural pectin from the fruit and increasing acidity, which helps pectin bonds form. Reduce the wine with spices before adding sugar — this concentrates flavour and cooks off harsh alcohol. Test for set on a cold plate: the jam is ready when a small spoonful wrinkles when pushed. A properly set wine jam holds its shape in a biscuit window and spreads cleanly without running.