Fruit freshness affects how the finished product sets. I would only make jam using fresh seasonal fruit. It has to be fresh and firm. When possible, use slightly under ripe fruit when pectin levels will be at the highest.
Always use a wide saucepan if you are lucky enough to have a preserving pan like the Kilner® Preserving Pan 8 Litre, that’s perfect. Never have the fruit more than half full in the pan.
I find preserving or granulated sugars are best. Granulated sugar is best for high-pectin fruits like citrus fruits and apples. Preserving sugar will help set low pectin fruits such as strawberries. I sometimes buy the pectin sugar which is very good when a fruit does not have a lot of pectin in it. Always make sure the sugar is completely dissolved before bringing to a boil. If not, the result will be grainy.
Skim any scum that rises to the surface, only when setting point is reached. If you keep skimming it off from the start, you’ll finish with no jam at all. Instead, wait until you have a set jam, then remove from the heat and stir in a small lump of butter. This will dissolve the scum almost instantly.
Temperature is everything in jam making, so it helps to have a sugar thermometer, the Kilner® Thermometer and Lid Lifter is the perfect tool for this. If the jam is not quite thick enough just keep boiling. If not set, continue to cook, checking every 5 minutes and do not overcook. To test if it’s set, place a small saucer into the fridge for 10 minutes and place a spoonful of the hot jam onto the plate and return to the fridge for a few minutes. Push the edges of the jam with your index finger – if it's set it'll be all wrinkly and crinkly.
Make sure your jars are well sterilised. I always wash mine in a water bath and let them dry out. It is important that you only sterilise your jars, bottles and lids or seals a short time before you are ready to fill them to ensure they remain warm for the filling process. For more information on sterilising your jars click here.
As an optional extra, I like to cover the surface of the jam in the jar with a wax disc. This helps prevent mould forming during storage. Seal the jar with a tight-fitting lid or cellophane disc secured with an elastic band. Always check your jars are sealed correctly. Store in a cool, preferably dark place. Only store in the refrigerator once opened.