Had a good long chat with Davy yesterday and picked up some tips.
1. Juice apples when fresh. You will get more juice. Don't wait for them to age, as the structure of the apple changes.
2. To reduce (concentrate) apple juice freeze it, don't boil it. You will get a toffee apple flavour from boiling.
3. Back sweeten with concentrated apple juice (see point 2) for the best flavour. Other methods not recommended if can be avoided.
4. pH of juice has to be right to keep aldehydes low. pH can only be effectively adjusted by blending.