Blanch whole peaches for 30 to 60 seconds to loosen skins, then transfer to ice water. Slip off skins, halve, remove pits, and slice. Immediately treat with an anti-browning solution: dissolve ¼ teaspoon ascorbic acid (vitamin C powder) in 1 quart of cold water and dip slices briefly, or toss slices with lemon juice (1 tablespoon per quart of fruit).
For best quality (desserts and eating): use the sugar pack method. Toss treated peach slices with ⅔ cup sugar per quart of fruit. Let stand 10 to 15 minutes until juices flow. Pack into rigid containers with ½ inch headspace.
For cooking, baking, and smoothies: flash freeze treated slices on parchment-lined sheet pans until solid, then transfer to freezer bags.
For a syrup pack (best color and texture retention): prepare a medium syrup (3 cups sugar in 4 cups water, cooled). Place treated peach slices in rigid containers, cover with cold syrup, keep fruit submerged with a crumpled piece of parchment, and leave ½ inch headspace.
8 to 12 months.
Thaw in the refrigerator for best texture. Serve while still slightly frozen for the best consistency — fully thawed peaches are softer than fresh. For pies and cobblers, use frozen or partially thawed.