Prunus spp., harvested before ordinary eating ripeness
“Unripe plum” covers many species and cultivars at a firm green stage. It is not one standardized ingredient: an immature European plum, Japanese plum, and native American plum can differ substantially in skin bitterness, acid, aroma, and the way the flesh holds the stone.1
Plums are climacteric fruits, so ethylene is closely involved in ripening. Firmness falls as cell walls change, sugar becomes more apparent against declining acidity, and skin and flesh pigments develop according to the cultivar.2
Maine orchards can grow European, Japanese, hybrid, and native-derived plums, but winter hardiness and bloom time differ among them. Several American-hybrid types were selected specifically for colder climates.1
Green skin does not always mean unripe: greengage plums remain greenish at full ripeness. A developmental description therefore needs more than color—firmness, seed development, aroma, and cultivar all matter.
Plums, peaches, and cherries are Prunus stone fruits. Slightly underripe plums can contribute more natural pectin than overripe fruit; some plum types are naturally high-pectin even at ordinary ripeness.3
European plums, Prunus domestica, tend toward meaty, semifreestone flesh and include prune plums and greengages. Asian plums, P. salicina, are commonly larger, rounder, clingstone, and melting. Their aroma is a variable mixture that can include almond-like benzaldehyde, floral linalool, peach-like lactones, and spicy methyl cinnamate.4
Footnotes
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University of Maine Cooperative Extension, “Types of Fruit Trees,” accessed July 17, 2026. ↩ ↩2
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U.S. Department of Agriculture Agricultural Research Service, “Effects of a Peach Antisense ACC Oxidase Gene on Plum Fruit Quality,” 2005. ↩
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University of Minnesota Extension, “Preserving Food at Home: Fruit Spreads,” accessed July 17, 2026. ↩
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Harold McGee, On Food and Cooking: The Science and Lore of the Kitchen, rev. ed. (Scribner, 2004), PDF p. 374. ↩