Umeboshi is a traditional Japanese pickle made from pickled plums. It has a unique sour and salty taste that is both refreshing and addictive. To make Umeboshi, start by washing and drying the plums. Cut them in half and remove the pits. Sprinkle the plums with salt and let them sit for a few hours to draw out excess moisture. Rinse the plums and pack them tightly into a jar. Add red shiso leaves for color and flavor. Let the jar sit at room temperature for a few weeks to ferment. The longer you let it ferment, the stronger the flavor will be. Umeboshi is commonly enjoyed with rice or used as a filling in onigiri (rice balls).