Plums

Plums: freshness and ripeness guide

Plums are climacteric stone fruit: picked firm and mature, they keep softening, juicing up, and developing aroma off the tree, but they gain little additional sweetness, so the sugar is largely set at harvest and colour is the best guide to a sweet plum. For black plums that will be ready later in the week, choose fruit with a deep, even purple-to-black skin and no green or pale patches near the stem, firm with just the first hint of give, and free of bruises, cuts, or soft spots. A dusty, silvery-white film on the skin — the "bloom" — is a natural waxy coating and a sign of fresh, lightly handled fruit, not residue to avoid. Ripen plums on the counter at room temperature over a few days; to speed things up, hold them in a loosely closed paper bag, optionally with a banana or apple, whose ethylene hastens softening, and check daily.

A plum ready to eat now yields to gentle pressure — press with the whole hand rather than a fingertip, which bruises the flesh — and is softest and most fragrant at the blossom end opposite the stem, giving off a sweet, slightly tart smell. It should feel heavy for its size, with taut, smooth skin. Because plums gain little sugar after picking, the fruit that is fully coloured and aromatic at purchase is the one that will taste best. Once a plum is ripe the refrigerator becomes useful: chilled, ripe plums hold for up to a week, and letting them warm toward room temperature before eating restores their full aroma.

A plum is past its window when the skin shrivels and wrinkles deeply, juice weeps or leaks, or the flesh turns brown and mushy, and any mould, sour or fermented smell, or seeping soft spot means it should be discarded rather than salvaged; light surface wrinkling alone is only water loss, and such a plum is still fine to eat or cook. The key cold-weather caution is chilling injury: plums sold here are imported and arrive firm, and refrigerating them before they ripen leaves the fruit to soften into a dry, woolly, or mealy texture, often browning internally instead of turning sweet and juicy — so ripen at room temperature first and chill only once ripe. In an Edmonton winter the same cold injures fruit left in a freezing vehicle, so carry plums indoors promptly rather than leaving them in an unheated car or garage.

Sources:

• UC Davis Postharvest Research and Extension Center — Plum and Fresh Prune: recommendations for maintaining postharvest quality (climacteric ripening, optimal handling, and chilling injury / internal breakdown in cold-stored fruit). https://postharvest.ucdavis.edu/produce-facts-sheets/plum-and-fresh-prune
• Purdue University Extension — Plums: selecting firm, well-coloured, unblemished fruit and ripening at room temperature before refrigerating. https://www.extension.purdue.edu/county/fulton/_docs/plums.pdf
• University of Minnesota Extension (Real Life Good Food) — Plums: judging ripeness by give and aroma, room-temperature ripening, and refrigerating only once ripe. https://reallifegoodfood.umn.edu/fruits/plums