umeboshi
Japanese ume fruit cured in salt and dried, often coloured with red shiso: intensely sour, very salty, soft.
Umeboshi are the fruit of the Japanese ume tree, a close relative of apricot and plum, cured in salt, dried in the sun and often coloured with red shiso. They taste sharply sour and strongly salty with a fruity undertone; the flesh is soft and wrinkled and surrounds a hard stone that is removed before mashing or chopping. Because they are so intense, they are used in small amounts, for instance as a filling for rice balls, alongside rice, in dressings or as a seasoning paste. They are sold in Asian grocery stores, many organic and health food shops, and online, either whole or as a ready-made purée.
Substitute:
There is no truly equivalent substitute, because the combination of sharp acidity, salt and ume aroma does not occur elsewhere. Umeboshi paste replaces whole fruit without compromise; ume vinegar provides salt and acidity in dressings and rice, but not the flesh. Preserved lemon or lemon juice with salt gives acidity and salt, but tastes of citrus rather than ume.