If you have bought some kiwi fruit to make this recipe and they are not yet ripe, leave them for a day or so in a bowl along with the apples and they will ripen more quickly.
Trivia
‘Umeboshi’ sauce is a typical condiment of Japanese cuisine made from plums. "Ume" actually means plums in Japanese. Is obtained by macerating the plums in salt, then adding a natural dye derived from an aromatic plant called ‘shiso’.