To sterilise glass jars and lids, place heatproof glass jars in an oven preheated to 180°C until warm to the touch, about 10 minutes. Remove from oven and place on a clean tea towel until completely cooled. While the jars are in the oven, place the lids in a pot of boiling water and boil until clean, about 2 minutes. Using a slotted spoon, remove the lids from the water and place on a tea towel until dry. Your jars and lids are now sterilised and ready to use.