Prepare your stone fruit: Wash the fruit thoroughly and remove the pits. You can choose to leave the fruit whole or slice them into halves or quarters, depending on your preference.
Make the brine: Dissolve the salt in water.
Place the stone fruit into a clean Mason jar, making sure to leave some space at the top. If you're using spices, you can also add them to the jar. Pour the brine over the plums, ensuring they are completely submerged. (Create more brine if needed to cover the ingredients)Leave about an inch of head space at the top. If you happen to have too much fruit in the jar, you can just simply remove some. Use a weight to keep the fruit under the brine. Secure with a fermentation lid or a swing top lid sealed loosely with a rubber band. If the jar is secured tightly, be sure to burp the jar (open the jar) daily to release the gas.
Allow the fruit to ferment at room temperature, away from direct sunlight, for about 3-7 days. Taste them periodically.
When ready. Remove the counterweight and store it the refrigerator to stop the fermentation process. If stored in the brine, the fruit should last up to 2 months.