Take the berries off the stalks using a fork then swill em in water and drain.
Into the jam pan and slightly over-cover with water. May wish to slap in juice of a lemon or two or a glug or two of PLJ. Up to a boil, simmer for about five minutes and get stuck in with a potato masher and a really mean attitude.
Cool the gunge down and process through the jelly bag, being really, really careful not to spill any wayward drops anywhere that doesnt look good with purple blotches.
I then poured into (thoroughly washed) plastic milk containers and store in the fridge.
Either make as jam with c1lb sugar to pint of juice but you will need to add pectin too (one sachet per two pints seems about right).
I instead usually churn out a batch of crab apple and strain that also overnight, aiming for about five pints of that to four pints of the elderberry.
Mix the two juices and then add your sugar - broadly same c1lb per pint of the mix - but you should be OK for pectin at least for a gentle set.
A breathtakingly good jelly when it works out perfectly and pretty good even when it doesn't. I even get 'reminders' at this time of year from people who have had my elderberry and crabble in years past to get busy and not to forget them. As luck would have it, making one 4pint brew of pure elderberry plus a six pinter elderberry and crabble has been keeping me out of mischief for much of the last week, with the latest lot just cooling!
The pure elderberry is extra faffing and the added pectin but is magnificent in taste, smell and appearance (pretty well gleaming jet black in the jars, it is so thick).