Plums are small, round stone fruits with juicy, sweet-tart flesh and smooth skin that ranges in color from deep purple to red to yellow. Fresh plums are available from May to late October. And though some varieties are grown specifically to be dried into prunes, most plums are meant to be eaten out-of-hand eating or used in both sweet and savory cooking.
A plum is a plum is a plum. Or so it would seem, given that most stores label them simply red, black, purple, or yellow. But, in reality, there are at least 200 varieties. Once harvested, plums don’t store well and must be shipped and sold within 10 days. So growers produce several varieties that ripen on a staggered schedule from mid-May through October to ensure constant supply. What this means is that the red or purple plums you saw on your last market visit are probably not the same varieties you’ll find on your next.
Pluots or apricots made a good substitutes.
Choosing plums for baking: Go for firm-ripe plums. The ideal plum for baking is neither supersoft nor rock hard but somewhere in between. Take a plum and squeeze it gently in the palm of your hand. It should smell fragrant and feel firm yet springy. These plums are easy to slice, and during baking they become tender without losing their shape or releasing too much juice. If you can find only very firm plums, let them ripen in a paper bag at room temperature for a couple of days. For eating, choose firm plums that give slightly to light pressure. Avoid fruit with cracks, blemishes, or soft spots. Don't be put off by the slivery-gray film that coats plums—it's natural.
Underripe plums should be stored at room temperature until they soften slightly. Otherwise, refrigerate ripe plums in a plastic bag for up to 4 days.