Speaking of her blackberry jam, Barb says, "I use the open kettle method. What's four hours out of a day?" The safest, and most laborious, home canning method involves packing the jam filled jars in a pressure cooker and effectively autoclaving them. The easiest, and most dangerous method, is open kettle where you cook the jam in a pot, pour the hot jam into canning jars and slap on a lid.