Wash, peel, core, and slice apples. I recommend slices at least 1/2 inch thick. Thinner slices are more prone to turning to mush
To keep apples from browning as you peel, place slices in a bath of lemon or citric acid water using 1 teaspoon of citric acid or 3 tablespoons of lemon juice for every quart of water
Drain apples, and pack apple slices into sterilized quart jars, pressing them down to fit as many as possible, leaving half an inch of headspace
Fit with lids and rings
Place jars in a water bath canner, which has the rack inserted to protect jars from direct heat
Make sure there jars are neither touching each other, or the sides of the kettle.
Place a second rack on top of jars, and weight down with a large, clean, brick or rock.
Gently fill kettle with water, to 2” above jar tops.
Place lid on canner
Bring kettle to a rolling boil, and continue boiling for 20 minutes.
Let kettle cool completely if possible before opening and removing jars to avoid breaking glass.