The small fruit ( Prunus mume) is similar to apricots but is commonly called in English as the plum. The fruits are preserved and turned into condiments and drinks throughout East Asia (e.g., the traditional Chinese plum sauce is usually made of the same fruit). You can buy an amazing range of umeshu from https://www.tokusen.store/en/.
As Shizo Tsuji notes in the pages of his famous cookbook Ume does not typically develop well, and it can be a bit sour, falling off branches during the moist rainy season. This is why the green fruits are sold in Japanese markets in a non-ripe state, so that cooks can make use of the fruits.
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The green ume season is from late May until June. When the fruit begins to turn yellow ume is great for making umeboshi and pickling. The Japanese are particular about the season in order to make the most efficient use of the ingredients.
RECIPE
Japanese Plum Wine- Umeshu
Ingredients
2 pounds green, unripen ume
1 1/2 lbs Chinese rock sugar White or yellow
Around 1.75 Liters of shochu or vodka
Method
If you'd like ume, soak it for between 2 and 4 hours. Drain and then make use of a toothpick or skewer to get rid of the dark stem pieces and any other lingering funny bits off the belly button of every fruit.
The sugar and the ume are placed in two clean (sterilize them, if would like) 2 – to 3-quart containers. Then add the liquor. Close the bottle and store it in a cool, dark location for three months at the most. Strain to serve and store. The fruit is said to be edible.