Chop the cabbage. Start by quartering and coring the head of red cabbage. Then, place the quarters into a large food processor fitted with an S-blade and pulse quickly until the cabbage is chopped into confetti-sized pieces. Transfer to a large colander.

Rinse the cabbage. Rinse the shredded cabbage thoroughly under cold water. Shake the colander vigorously to remove excess water, ensuring it isn’t soggy.

Season the cabbage. Move the drained cabbage into a large mixing bowl. Sprinkle the sumac and Kosher salt and massage the mixture well with your hands. Allow this to sit for 15 minutes to deepen the flavors.

Pickle the cabbage. Combine the vinegar and water in the bowl, mixing well. Transfer the cabbage mixture (including the liquid) to a large half-gallon mason jar or a couple of smaller jars. Pack the vegetables tightly to ensure they are submerged in the liquid and seal with a lid. Refrigerate for at least 3 hours before serving. The pickles will maintain their deliciousness for up to 4 weeks if stored properly.