Crystallising Jam

Our answer

Nigella's Chilli Jam (from NIGELLA CHRISTMAS) should keep for up to a year, if stored in a cool, dry place away from direct light. Opened jars should be kept in the fridge and used within one month. If the crystals are forming on the top of an opened jar then it is probably caused by the jar not being sealed tightly and some evaporation ocurring.

However if the crystallisation is ocurring in unopened jars then it is most likely that some of the sugar was not quite completely dissolved before the chopped peppers were added and the mixture was boiled. Sugar likes to be in crystal form and over time any very small crystals of undissolved sugar will start to draw molecules of sugar towards them, re-forming crystals. When making the jam you need to make absolutely sure that the sugar is completely dissolved, with absolutely no traces of crystals. Sometimes this can take much longer than expected. For the jars that have crystallised, it is possible to re-warm the jam and dissolve the crystals before using. When you open a jar, decant the mixture into a saucepan and warm very gently, until the crystals have dissolved completely, but do not let the jam boil. Cool slightly and transfer to a clean jar then cover, refrigerate and use within 1-2 weeks.