25grams(4 teaspoons) powdered unsweetened apple pectin
15grams(1 tablespoon) fresh lemon juice or ½ teaspoon citric acid powder
Instructions
Make a puree of wild plums by heating them on a baking sheet in an oven until hot, (325 F) for 15 minutes. You can also freeze very ripe plums, thaw and mush them around in a bowl.
Cool the plums until you can handle them, then mash them in a bowl, adding a cup or so of water to help release the puree. If you have really nice, large wild plums, you may not need all of the water, if your plums are small, you may need more.
Mush this puree through a collander over a bowl to catch the skins and stones, then reserve the puree that passes through the holes. Allow the puree to cool, then measure out what you need.
Mix the sugar and pectin, then puree with cool plum puree in a blender. Transfer the mixture to a stove and cook on medium, and then high heat, whisking occasionally until it comes to a rapid boil. Cook until the mixture hits 220 F on the thermometer.
Beat in the lemon juice, transfer to pint jars and can in a water bath for 10 minutes or the recommended time for the jars you're using.