I've been making Damson Jam. I'm sharing the method I use to make my jam, I've used this method for about 4 years now and it usually works very well.
Recipe from Delia Smith.
1.3 kg fruit to 1kg of preserving sugar.
Pick out any stalks - there weren't many as weed done most of that when we froze the fruit back in the summer.
Simmer the fruit in 15fl oz of water till soft.
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At this point I de-stone the jam. My hubby likes the stones left in, but I don't. So we compromise and take out most, leaving a few in and a few whole fruit. this can take quite some time!
While I'm doing this the oven goes on at 180. and the sugar goes in a heat proof bowl to warm.
When done - fruit and sugar in the pan, stir lightly and leave on a low heat until the sugar has dissolved.
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Then boil rapidly for 10 minutes. turn off the heat and check for set. put a little on a cold plate and allow to cool, if it wrinkles when pushed with your finger it's done. If not, boil for another 5 mins and test again. do this until the wrinkle check works (usually takes 15 mins boiling for me.)
Let settle for a few minutes and then pour into warmed, sterilised jars - put on lid and allow to cool completely.
store in fridge once opened - makes a great gift.