A good pie apple has to be able to hold its shape when cooked, give off some juice so that the pie won’t be dry, and have good flavour. The apples should also be very aromatic, and should be tart, so that sugar can be added to the pie, though some good pie apples have enough of their own sweetness that you will want to cut back on added sugar when using them. Ideally, a good pie apple is also slow to brown, to give you a little time to finish slicing them all and then arrange them in the pie dish.
Most pie apples aren’t actually for home use — they’re for commercial bakers. Some of the best pie apples in North America, such as Winesap and Northern Spy, aren’t often seen in supermarkets, though Northern Spy is used a lot by makers of frozen pies.
Rarely is an all-purpose apple also good for apple pies — Bramley is one exception. One of the more prevalent apples in Canada that is used for pies, the all-purpose McIntosh, makes truly indifferent, mushy pies (but the McIntosh does cook down into okay applesauce and apple butter.)