Remove calyx of the fruits with a toothpick or skewer.
Wash fruits in baking soda and water scrubbing the skin to get off any residual dirt. Dry fruits with a dish towel and then let air dry completely.
Sterilize a large jar, mason jar or pickling jar, by boiling for 10 minutes. Remove jar and let air dry. Put jar lid in the residual hot water for 1 minute.
You can further sterilize jar by rubbing 20% proof alcohol like vodka with paper towel, or you can skip this step.
Layer bottom of jar with sugar, then add a layer of ume, keep alternating between the two until the jar is filled. Make sure last layer is sugar. You want the ume to be sandwiched by the sugar so mold doesn't grow.
Let ferment in a dark place like pantry/cabinet/closet for 3 months~100 days. When time is up, remove the fruits from the syrup and enjoy as is or you can not remove the fruits and let it ferment for 1 whole year! Make sure to write the date on top of jar if you are forgetful like me.