In New Zealand it is still plum season in the Oratia orchards! But is it so hot that plums don't last long after picking, so I had about 1 kg that was far too ripe and soft for eating. I washed and then put the plums in a pot with a little water and boiled them, then I strain them to discard stones and leftover skin and tasted the paste. I usually add 50-60% of sugar (I don't like the 1kg fruit for 1kg sugar ratio they do in NZ), but this paste was already sweet! So I added just 2 tbsp of brown sugar and a pinch of citric acid (as a preservative) and, fearing that the jam wouldn't set, 1/3 tsp of agar agar. If I were to keep this jam longer maybe I would have added more sugar, but I only made 5 small jars and two are gone already!