This weekend we found an enormous blackberry patch, completely by chance. About 500g came home in a bag, just a small picking but we will try to go back for more soon.
Since wild blackberries tend to be very pippy jelly seemed to be a better idea than jam. 400g went into a pan with a little water to be boiled and mashed, then left to drip through a jelly bag overnight. I had a flash of inspiration and realised I could hang a jelly bag from the extractor fan knob. Oh, and the missing 100g of berries were eaten :)
The juice in the bowl measured just over half a pint, so it was mixed with the juice of a lemon and 8oz jam sugar (the stuff with pectin already added in) and boiled vigorously for 4 minutes. A small test on a chilled plate showed it had reached setting point so it was poured into jars.
400g of berries gave about two and a third small jars of jelly.
The part jar has already been eaten!