While the apple butter is cooking, wash six or seven jam jars and lids in hot soapy water. Rinse them well and place them on a baking tray. Heat the oven to 100°C and slide the tray in for 30 minutes, or until the jars are completely dry. Once the apple butter is done, spoon it into the hot, clean jars and seal them tightly with the lids. Store in a cool, dark cupboard; the preserve should keep for a year.