The cold plate test
This test is a way to check that jams and jellies have the right consistency. Before you start cooking, place a small plate in the freezer. After the suggested cooking time, remove the pan from the heat to stop cooking and spoon about 1 tsp of jam on the cold plate. Return the plate to the freezer and let cool for 1 to 2 minutes. The jam should thicken. If not, continue cooking and repeat the cold plate test every few minutes.