Finally got time to make the crab apple jelly. I got about 800mls of juice from 4kgs of crab apples which wasn't very much so I'm not sure if next time I need more water. Anyway, ended up with 3 1/2 small jars of nice pink jelly. Unfortunately though there was quite a lot of scum (froth?) on top and though I tried to scoop it off before putting the jelly into the jars, it still managed to permeate the jelly so it's not crystal clear. However, it tastes just fine.