These two late summer/early fall treats make for the most amazing flavor when combined. The sweetness of the blackberry combined with the tartness of the plum are exceptionally balanced in jam!
- Prepare the boiling water canner before starting to cook your jam. (Fill the canner/stockpot at least half full of enough clean, warm water so the level will be at least 1" over the top of the filled jars once they're added).
- Wash, pit and chop plums w/ skins.
- Wash and crush blackberries w/ potato masher.
- Place plums and crushed blackberries in large pot.
- Add pectin a little at a time to plums and berries, stirring constantly.
- Heat on high stirring constantly until mixture comes to a FULL boil.
- Add sugar ALL at once, stirring.
- Bring mixture back to a full hard boil, stirring constantly.
- Use potato masher to carefully further crush plums and berries in pot.
- Boil for 5 minutes.
- Skim off foam, if present.
- Place in sterilized, hot jars, leaving 1/4" headspace.
- Wipe edges of jars with clean cloth, place lids and screw on bands fingertip-tight.
- Process in a boiling water bath for ten minutes at sea level (over 1000 feet, add one minute of processing for each 1000 feet in altitude).
- Remove from water and place jars on a cloth-protected counter or cooling rack to cool undisturbed for 24 hours.
- Remove rings from sealed jars and store; put any unsealed jars in the refrigerator and use first.
Turned out beautifully, what a lovely way to use some of my excess summer produce. I used jam sugar so left out pectin but otherwise made as directed.