Peel (optional, but recommended for best texture), core, and slice into wedges or pieces. Immediately treat with anti-browning solution: dissolve ½ teaspoon ascorbic acid in 3 tablespoons water and sprinkle over slices, or toss with lemon juice (1 tablespoon per quart of slices). Drain well.
For pies and baking: flash freeze treated slices on parchment-lined sheet pans until solid, then transfer to freezer bags. You can measure out a pie's worth of slices per bag for convenience. Some bakers prefer to toss slices with sugar and spices before freezing so the filling is ready to pour directly into a crust.
For applesauce or purée: cook apples down into sauce, cool completely, and freeze in measured portions (cups or pints) in rigid containers or flat-packed bags.
8 to 12 months for treated slices. 6 to 8 months for applesauce.
For pies and baking: use directly from frozen. Arrange frozen slices in the pie shell or baking dish — the filling will take slightly longer to bubble but the results are excellent. For sauces and smoothies: thaw in the refrigerator or use frozen.