A process used to keep morsels firm in strawberry jam can be applied to other fruit such as apricots and plums. We applied it to Victoria plums in Southfields last September.
The process is simple. Instead of cooking the jam right away, the mix of fruit, sugar and lemon juice is heated several times and left to cool down for sugar to penetrate the fruit. Jam is then cooked as usual and the result is firmer morsels, slightly chewy.
An other step can be taken when a lot of liquid has come out of the fruit before the final cooking. Fruit is put aside and juice is reduced over a slow heat. Fruit is then added back and the jam cooked. Very useful for fruit containing a lot of water and little pectin, typically strawberries.
We applied both principles to the victoria plum jam we made last September: the mix of stoned plums cut in two, sugar and half a lemon juice per kilo of fruit was heated up to boiling point and then left to cool down. Same operation a day later. On the third day, we reduced the juice over a strong heat for twenty minutes or so before adding the plum morsels and cooking the jam for about ten minutes.
The jam was made with fruit given by a friend who has a plum-tree in his Raynes Park allotment.