4 cups of fresh, ripe boysenberries
4 cups of granulated sugar
The berries don't require any additional pectin as they are naturally high in it.
Clean the boysenberries thoroughly in cool water and then crush them slightly. Put them through a food mill or place them in a fine mesh sieve and crush them gently with your hands by pressing against the bottom. Do not puree the berries, as this can cause a change in acidity, resulting in a weak jam. Place the crushed berries into a large saucepan and turn the heat to medium-high. Bring to a boil and then reduce the heat to medium-low. Add the granulated sugar to the berries, stirring constantly until it is completely dissolved. Increase the heat to medium-high and boil for another five minutes, stirring often, or until the gelling point is reached.
Check for the gelling point by removing the saucepan from the heat. Dip out a small amount of the boiling liquid and place it on a small saucer. Place the saucer in the freezer and wait two to three minutes. Remove the saucer and check the liquid for gelling. If it has gelled, the jam is ready, but if it is still liquid, more cooking time is needed. Try boiling for another five minutes, then check it again.
Processing and Storage
Once the gelling point is achieved, skim off any foam on the surface of the boysenberry jam liquid. Pour immediately into the hot, sterilized jars, leaving about 5mm of space at the top of each. Secure the lids in place tightly and prepare a hot water bath for processing. Bring enough water to a boil in a large stockpot to cover at least 2-3 cm over the top of the jars. Lower the jars into the boiling water with metal tongs, then cover the pot. Boil the jam jars gently for about five minutes.
Use the metal tongs to remove the jars from the boiling water, and place them on clean towels to cool. Allow them to sit undisturbed for at least 12 hours. Disturbing them before this time can result in a weak jam by breaking the gel. As the boysenberry jam cools, the jar lids will begin to pop. This indicates that the jar has sealed properly. If a jar fails to seal, it should be stored in the refrigerator for no longer than 90 days.
Label each jar with the contents and date. Store sealed jars in a cool, dry place until ready for consumption. Sealed jars of boysenberry jam will keep for up to one year, although it is better to consume the jam within a few months. As a rule, the shorter the storage time, the more flavour the jam will have.
Use a large, non-reactive saucepan, large stockpot with lid, metal tongs and three 240ml (1/2 pint)-pint glass jars with clean lids to prepare the jam. Do not use larger jars, as this can result in a weaker gel due to excess heat during the cooling process. Sterilize the jars in boiling water for 10 to 15 minutes before using, and make sure they are still hot when pouring the jam.