There are various ways of checking if your jam is set, the most reliable is using a digital thermometer as it takes the guesswork out of the process and ensures you don’t overcook the jam and preserve all the fruity flavours. Another test is to put a saucer in the freezer when you start your jam making. When you think the jam has set, remove it from the heat and spoon a teaspoonful onto the chilled saucer. Leave a minute, then push the jam with your finger, if it wrinkles the jam is ready, if not return to the heat and boil for a further 5 mins before retesting.