Rinse 1 pound (about 3 cups) kumquats. On 1 side, slit each lengthwise to the center. Put in a 3 1/2- to 4-cup jar with 2 to 3 tablespoons drained large capers. Add 1/4 cup kosher salt.
Cover airtight and freeze at least 8 hours. Place jar upside down in the refrigerator and let stand 24 hours. Use, or chill up to 1 month, turning jar over every 2 or 3 days to keep salt distributed.
Nutritional analysis per kumquat.