What is important to achieve a quality jam which sets ?

* Full flavoured fruit, which is just ripe, not over ripe
* A balanced reliable recipe, including enough sugar so that 60% of the finished product is sugar
* Gentle cooking of the fruit until soft, particularly important if the fruit has skins
* Granulated cane sugar that has been warmed in an oven and is stirred frequently until dissolved
* Enough heat to achieve a genuine rolling boil
* Not over boiling, many recipes only require 5-10 minutes boiling
* Testing for a set as soon as possible, using a thermometer 104.5℃, or the wrinkle test, or the flake test, my favourite
* Allowing the finished jam to stand for 5~10minutes, skimming off any scum, potting-up, sealing and leaving to set undisturbed.