This is the Blackberry & Apple syrup I made a few days ago. It contains about a pound of blackberries, a large cooking apple and a couple of small eating apples (leave those out next time - they don't mush down as quickly as cooking apples, and as a result you overboil the blackberries, which destroys the flavour). Cook and strain as for jelly, but then heat the juice with sugar (8-12 oz per pint of juice) for as short a time as possible (bring to the boil and simmer until the sugar is thoroughly dissolved), then put into sterilized bottles.
Finding suitable bottles was the hardest part. You need glass bottles with metal tops - most bottles have plastic caps nowadays. Only the more expensive drinks have metal tops. This was a lovely bottle but I just couldn't get the label off, no matter how I tried. The label seems to be made of plastic, not paper - God knows what it's stuck on with.