Sterilize the jars and lids by boiling them in water for 10 minutes. Keep them hot until ready to use.
Prepare the Fruit:
In a large pot, combine the raspberries and chopped peaches. Mash them slightly with a potato masher to release their juices and break them down a bit.
Add Lemon Juice and Pectin:
Stir in the lemon juice and powdered fruit pectin.
Bring to a Boil:
Place the pot over medium-high heat and bring the mixture to a full rolling boil, stirring constantly.
Add Sugar:
Add the granulated sugar all at once and stir to dissolve. Return the mixture to a full rolling boil and boil for exactly 1 minute, stirring constantly.
Skim Foam:
Remove the pot from heat and skim off any foam that may have formed on the surface.
Fill the Jars:
Carefully ladle the hot jam into the prepared jars, leaving about 1/4 inch of headspace at the top. Wipe the rims of the jars with a clean, damp cloth to ensure a good seal.
Seal the Jars:
Place the lids on the jars and screw on the bands until fingertip tight.
Process the Jars:
Process the jars in a boiling water bath for 10 minutes to ensure they are properly sealed.
Cool and Check Seals:
Remove the jars from the water bath and let them cool completely on a towel or wire rack. You should hear a popping sound as the jars seal.
Once cooled, check the seals by pressing the center of each lid. If it doesn’t pop back, the jar is sealed. If any jars did not seal properly, refrigerate and use those first.
Store the Jam:
Store the sealed jars in a cool, dark place for up to 1 year. Once opened, refrigerate and use within a few weeks.