Sterilisation
Efficient sterilisation is the key to successful jam making. You need to ensure you eliminate all food-spoiling yeasts and moulds that are present in your ingredients and in the jars you will fill.
Fruit that is cooked with sugar to the correct temperature and clean glass jars that have been heated to 110°C are going to preserve your jam for at least 12 months.
To sterilise your jars, wash them in warm soapy water and rinse thoroughly. Place them, open-side up, on a baking tray and put in an oven preheated to 110°C and leave for 30 minutes. To sterilise lids, clips or rubber seals, place in a pan of water over high heat, bring to the boil and boil for 5 minutes, then turn off heat and leave to rest.
I advise you to begin the sterilisation process when setting point is reached. You can always turn your oven off and leave the jars resting in the warm oven before using them – just don’t allow them to become cold. Hot jam should always go into warm jars and be sealed with warm lids so that a seal is formed inside as the warmth pushes the air out.
You can also turn your jars upside down to help push out the air but be careful with high-pectin fruit as they will set quickly and you’ll have levitating jam.