Save those watermelon rinds from their usual fate on the compost or garbage heap! Instead, ferment them into a healthy treat to enjoy for months. Make fermented watermelons by combining the white inner rind of the already-eaten watermelon with salt and water. Leave the mixture at room temperature for one to two days and it ferments on its own into a slightly soured pickled watermelon. This natural fermentation process, called lacto-fermentation, uses bacteria present in the environment to break down sugars in the watermelon rind, while the salt acts as a preservative and helps to control the fermentation process.
Prepare the watermelon by removing all of the pink inner flesh, using a spoon. Use a knife to remove the outer green skin, leaving just the inner white rind. Cut the remaining rind into 1-inch pieces.
Mix a brine using 2 tablespoons of salt and 1 quart of water and stir until the salt is completely dissolved. Pack the watermelon rinds into the jar with the brine, ensuring the watermelon rinds are covered by at least 1 inch of brine. Add any spices you are using to the jar.
Cover the jar with a kitchen towel and secure the towel with a canning ring. Leave the jar on your counter for one to three days to ferment; the process should be done at room temperature, ideally between 60 and 70 degrees Fahrenheit.
Place the jar in your refrigerator, where your fermented watermelon rinds will keep for two to three months.