Prepare your jars, start your lids to simmering and bring your canning pot to a boil.
In a large pot, combine blueberries, blackberries and sugar. Stir well, set the heat to medium and bring to a simmer. Pour in lemon juice and add lemon zest; stir well, increase the heat to high and bring to a boil.
Reduce heat slightly and cook for 30 minutes or until it starts to thicken, stirring often.
Add pectin, stir very well and bring the heat back to high; boil for 5 minutes or until thickened, stirring frequently. To know if it’s ready, dip a metal spoon in an ice water bowl, dry it off and scoop up some jam. Let it cool off to room temperature. If it sets up, it’s ready otherwise cook a little longer. Keep in mind that as the jam cools and sets up, it will get thicker.
Remove from the heat, fill the prepared jars, wipe rims, apply lids and screw bands, and process in a boiling water bath for 10 minutes.
Remove from water and allow jars to completely cool on a wire rack. Makes 7 jars of 250ml.