Elderberry & Apple Jelly

After cooking the fruit yesterday evening, and straining for 24 hours, I had a pan full of elderberry and apple juice this evening. I think, in future, I might cook and strain them separately: I think the elderberry would have yielded more without the almost mucilaginous apple pulp. However, 450g of sugar per 600ml of juice, brought to the boil until it reaches 104°C, as normal. This one was quite exuberant, and almost boiled over several times, but we got there in the end. There was quite a lot of foam, which I managed to contain to one jar, which will be hidden away for us to eat on our own. The rest look rather presentable, with a dark, rich jelly.