Peel 1 pound golden or red beets, then cut into matchsticks. Toss with 1 1/2 teaspoons kosher salt; set aside until they release their liquid, about 15 minutes. Rinse, drain and pat dry; transfer to a glass bowl. Bring 1 cup cider vinegar, 1 cup water, 1/2 cup sugar, 1 halved serrano chile (seeded, if desired), 4 strips grapefruit zest, 1 1/2 teaspoons peppercorns and 1/4 teaspoon salt to a boil in a small saucepan. Pour over the beets. Let cool, then cover and refrigerate at least 1 day and up to 10 days.
TIP: Use these pickled beets as you would sauerkraut-on top of a sandwich, burger or hot dog.