Before beginning, make sure you have all the ingredients and equipment (canner, jars, lids, utensils, etc.) ready to go. Wash jars and lids in soapy hot water. Fill a water canner half full of water. Bring this to a low simmer. Fill jars with water and put on an elevated rack in canner , while water is simmering, to keep jars warm. (Or you can set jars on dish towel on a cookie sheet and keep in oven at 250 degrees for 20 minutes for same effect). At the same time, I start a teapot with water going, (so I will have boiling water for the jar lids later on).
Put flat jar lids in small bowl and set aside. In a large bowl, measure out the exact amount of sugar needed. Set aside.
Crush the berries one cup at a time (it is very easy if you use a potato masher). Put the finely crushed berries (6 cups total) into a large stock pot. Stir the box of Pectin into the berries. Bring this mixture to a full rolling boil on high heat, stirring constantly (a rolling boil is when it is boiling hard, it won't stop bubbling even when stirred). Once berries are at full rolling boil stage, stir in all of the sugar quickly (all at once). Stir well to combine.
Plan ahead... The amount of berries needed is 6 cups CRUSHED berries. Make sure you have a couple cups of extra boysenberries before beginning, to ensure you have the correct amount necessary for this jam!
Boysenberry Jam https://www.thegratefulgirlcooks.com/boysenberry-jam/