Wash and drain the fruit, then mash, crush or liquidise and place in a large saucepan.
Add the Sure-Set and heat stirring until it is dissolved, then bring to the boil and boil vigorously for 4 minutes. (See 'Adding Sure-Set' for details on boiling and timing).
Pot and cover in the usual way; label and date. (See 'Potting and covering' for details).