3lbsplums, sliced and pits removed (leave skins on) (1360 grams)
5cupsgranulated sugar(1000 grams)
½cupbottled lemon juice(120 ml)
Zest of 1 orange
Combine the raspberries, sliced plums, sugar, lemon juice, and orange zest in a large heavy-bottomed pot. Place over medium high heat and stir frequently as the sugar dissolves and the fruit begins to release its juices.
Continue to cook, stirring frequently as the jam simmers and thickens. Skim any foam off of the surface with a spoon.
(Optional) While the jam is simmering, remove plum skins with a spoon. It is slightly tedious but I prefer the texture of the jam without the skins.
(Optional) If you prefer fewer raspberry seeds, simply place a mesh strainer over the pot. Ladle ⅓-½ of the mixture into the strainer and push it through with a spatula back into the pot. Discard raspberry seeds.
Once the jam is reduced and thickened (see tip above), remove from heat and ladle jam into sterilized jars. Top with a lid and screw on with a ring.
Process jars in a water bath for 10 minutes (15 minutes for 5,000+ ft elevation). Remove from water bath and let cool. Check that lids have sealed by pressing down into the center of each one. It should not move.
Store jam in a cool dry place like a pantry and consume within 1 year.
Note: I used a variety of plums in this jam. Use whatever you have available at your grocery store or farmer's market.