After salting the ripe Koshu plums from Yamanashi Prefecture, they are dried in the sun in the traditional way, left in barrels for at least three months, and then soaked in kelp liquid. The umami flavor of the kelp softens the acidity of the plums and makes them easy to eat. It is not too sweet and has a taste that goes well with rice. After salting the ripe Koshu plums from Yamanashi Prefecture, they are dried in the sun in the traditional way, left in barrels for at least three months, and then soaked in kelp liquid. The umami flavor of the kelp softens the acidity of the plums and makes them easy to eat. It is not too sweet and has a taste that goes well with rice.