I've made a batch of plum jam which is not very firm. Can I re-boil the jam until it becomes the right consistency or are there any other tips, please?
Runny jam is sometimes caused by the chemical make up of the fruit, or getting the pectin too hot. You may be able to "force" it to thicken by cooking it again and bring it to a good boil. When the sugar gets hot enough it will thicken when it cools. It is the same concept as when making candy. As the sugar gets hotter it eventually reaches the hard crack stage. You don't want it to reach the hard crack stage, but you can refer to a candy thermometer for the desired temperature. This has worked for me on occasion.
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