Step 1: Prepare the watermelon rind. Using a sharp knife or vegetable peeler, carefully remove all the dark green outer skin and any remaining pink flesh from the watermelon rind. Cut the white rind into 1-inch pieces.
Step 2: Brine the rind. In a large non-reactive bowl, combine the cut watermelon rind with the pickling salt. Toss well to coat. Add enough cold water to cover the rind completely. Place a plate on top to keep the rind submerged and let it stand at room temperature for 2-3 hours. This step helps draw out excess water and firm up the rind.
Step 3: Rinse and drain. After brining, drain the watermelon rind in a colander and rinse thoroughly under cold running water for several minutes to remove excess salt. Drain well and set aside.
Step 4: Prepare the pickling liquid. In a large non-reactive pot or Dutch oven, combine white vinegar, water, granulated sugar, mustard seeds, celery seeds, red pepper flakes, dried chili peppers (if using), cinnamon stick, whole cloves, and turmeric (if using). Bring the mixture to a boil over medium-high heat, stirring until the sugar dissolves completely.
Step 5: Cook the rind. Add the rinsed and drained watermelon rind to the boiling pickling liquid. Reduce the heat to medium-low and simmer gently for 20-25 minutes, or until the rind becomes translucent and tender-crisp. Do not overcook, or it will lose its desirable crunch.
Step 6: Pack into jars. Carefully ladle the hot watermelon rind and pickling liquid into clean, sterilized pint jars, leaving about 1/2 inch headspace. Ensure spices are distributed evenly among the jars. Remove any air bubbles with a clean utensil.
Step 7: Seal and store. Wipe the rims of the jars clean, center the lids, and apply the bands until fingertip tight. If you plan to can them for shelf stability, process in a boiling water canner for 10 minutes. Otherwise, allow them to cool to room temperature, then refrigerate.
Step 8: Chill and enjoy. For best flavor, allow the pickled watermelon rind to chill in the refrigerator for at least 24-48 hours before serving. They will keep well in the refrigerator for several weeks.