Choosing plums for baking
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. I tried dozens of kinds of plums and found that the variety doesn’t matter much. The fruit’s ripeness, however, matters quite a bit.
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 the shortcakes, however, you can get away with using underripe plums because the caramelization softens and sweetens the fruit.