Rusty Hinge writes

till very soft, then strain through a fine cloth or use a fruit
press to extract juice,
Would a juicer do this?

No. You need to cook the whole apple including pips, or you might not
get enough pectin.

That's not a problem, since you don't strain or juice until after
cooking, so you already have picked up the pectin.


If you can get hold of any sort of quince, one or two of the Japanese
types or one oblongata will add a delicate flavour to the jelly.

You don't need that for crab apple jelly as they have a fine enough
flavour on their own - indeed, I'm not sure the aromatic flavour of the
quince would go that well with the sharpness of the crab. But quince is
an excellent idea for adding to jam made from dessert or cooking apples.

--
Kay