Steam plums (pitted or not) with 1 cm of water in a pot with the lid closed until they are soft and juice comes out. Let cool down a little (approx. 50 - 80 ° C). Pass through a coarse (salad) sieve to separate from stones and shells.
Mix the plum jam with the rest of the ingredients and simmer over a very low heat for about 30 - 45 minutes (do not boil bubbly!). Stir occasionally to more often, otherwise the thick sauce will bake. Then fill into clean, sterilized screw-top jars.
Due to the high content of vinegar, salt and sugar, the preserve lasts longer than normal jam. The sauce tastes really delicious for around 2 - 3 years, after which it loses a bit of whistle and sharpness. If opened, it will keep for 2 - 4 months without refrigeration.