I made 12lb plum jam last weekned and am about to make some ore tomorrow.
This year's batch was better than last years's (my first attempt).
I'm using Victoria (I tihnk) plums from the garden - they're red skinned with yellow flesh and lovely and sweet.
I stoned but did not skin my plums first. Uisng 2.7kg (6lb), I put them on to simmer for half an hour with 900ml water, together with a few crushed stoned and a stick of cinnamon. Nex time I'll put in slighlty less sugar just to expreiment.
I actually simmered them for slighlty more that half an hour, as the plums weren't quite really soft.
Then I put in 2.7kg granulated sugar - all the recipes I have read have said that using caster sugar can casue probelms.
Once it had dissolved, I then put up the gas burner to bring it up to the boil. I actually ended up squeezing half a lemon in to it, as it seemed to be taking such a long time to get to setting point. I ended up giving up on the thermometer and using the wrinkle tst - althigh I think that last year, when I didn't have the thermometer, I ended up over cooking it, as dh has commented that last year's batch is darker than this year's.
This year I also invested in a preserving pan from Lakeland Plastic - althoguh I am sure it is not essentail!
I did stir (with a long handled wooden spoon) regualrly, but not continuously.
I've also tried making pear jam for the firs time this year - it is very tasty, even if it hasn't set properly (didn't use the wrinkle test, althugh I did use 3 lemons to encourage setting but suspect it wasn't fully up to temperature as I was slightly missuing the temomenter - made this badge before the plum jam)