When making jam, always use fruit that's in peak condition ... How to sterilise jam jars: wash in soapy water, rinse well and then place into a cool oven - 130C/250F/Gas ½ - for 15-20 minutes.
If making raspberry jam, it's crucial to use sterilised jars to store it. To clean the jars, preheat the oven to 140C/120C Fan/Gas 1. Wash the jars well in warm soapy water then rinse thoroughly ...
Using a potato masher ... ladle it into clean half-pint jars or other air-tight containers. Allow to cool, then store in the refrigerator for up to a month. Make jam with whatever is in season!