Step 1: Prepare the watermelon rind. Carefully trim all the red flesh from the watermelon rind. Using a vegetable peeler, remove the tough, dark green outer skin, leaving only the pale green and white part. Cut the cleaned rind into 1-inch pieces, cubes, or strips.
Step 2: Brine the rind. Place the cut rind pieces into a large bowl. Sprinkle with kosher salt and toss to coat evenly. Cover the bowl and let it sit at room temperature for at least 4 hours, or preferably overnight (up to 12 hours). This step helps draw out excess water and ensures a crisp texture.
Step 3: Rinse and drain. After brining, drain the rind in a colander and rinse thoroughly under cold running water to remove all excess salt. Squeeze gently to remove as much water as possible. Set aside.
Step 4: Prepare the pickling brine. In a large non-reactive pot (stainless steel or enamel), combine 4 cups of water, apple cider vinegar, granulated sugar, whole cloves, mustard seeds, and cinnamon sticks. Bring the mixture to a boil over medium-high heat, stirring until the sugar is completely dissolved. Reduce the heat and let it simmer for 5 minutes to infuse the flavors.
Step 5: Cook the rind. Add the rinsed and drained watermelon rind to the simmering brine. Bring the mixture back to a gentle simmer and cook for 10-15 minutes, or until the rind becomes translucent and tender-crisp. Be careful not to overcook; the rind should still have a slight bite.
Step 6: Pack the jars. Carefully transfer the hot watermelon rind pieces into clean, sterilized pint jars, leaving about ½ inch of headspace. Pour the hot pickling brine over the rind, ensuring the rind is completely submerged. Distribute the spices evenly among the jars.
Step 7: Seal and cool. Tap the jars gently to release any air bubbles. If necessary, add more brine to maintain headspace. Wipe the rims clean, place lids, and screw on bands until fingertip tight. Allow the jars to cool completely at room temperature. As they cool, the lids should ‘pop’ indicating a seal.
Step 8: Chill and enjoy. Once cooled, store the sealed jars of pickled watermelon rind in the refrigerator. For best flavor development, allow them to mellow for at least a week before opening. They will keep well in the refrigerator for several months.