The setting of jam depends on its pectin content, and some types of fruit have a higher pectin content than others, so that they are good ‘mixers’ with other fruits. Cooking apples, blackcurrants, damsons, gooseberries, plums, quinces and redcurrants are all high in pectin, and preserves made with them always set well. Fresh apricots, early blackberries, greengages and loganberries have a lower pectin content.
Fruit and vegetables which are low in pectin include late blackberries, cherries, elderberries, marrows, medlars, pears, rhubarb, strawberries and tomatoes, and these need mixing with high-pectin fruit, or juice made from such fruit, while acid will help to release the pectin.
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