Call out the drupes! I was excited to see stone fruit as the topic of Tigress’s September Can Jam. Stone fruits are botanically known as drupes (from a Greek word for olive) because the real seed is protected by a stone-like shell, which is in turn surrounded by the fruit and an outer skin, the parts that we eat. I’ve been cooking with the drupes — cherries, apricots, peaches, plums and nectarines all summer (the apricot-nectarine jam was especially good) — and decided to try my hand at plum jam and plum sauce for the Can Jam.
While there are freestone plums, most of the varieties that I have recently found interesting are clingstone. When I made sorbet and the first version of this jam with tiny sugarplums, I discovered that I could microwave them briefly and use a knife and fork to separate the flesh from the seed. The jam was very tasty but a textural disaster since the sugarplums had such a high ratio of skin to flesh. So this time, I used fleshier plums – red all the way through – and cut the flesh off. Since I wanted to use the inner kernels, the real seeds, I needed to crack the hard shells, which I konked with a hammer, since a nutcracker wouldn’t work on those slippery shells. Luckily, the pungent brown skin slipped right off. Otherwise, you’d have to parboil the kernels.
The other trick was to simmer the plums in water to soften and almost dissolve the skins before adding the sugar to make jam. This mostly worked, but I ended up fishing out some hardened ropes of skin before jarring the jam. Next time, I’ll cut the pieces smaller, or puree the plums, skins and all, before cooking.
Now for the tonka bean. A couple of months ago, my peripatetic pals visited a certain spice market in Paris that I like very much and brought me a little pouch of tonka beans, among other goodies. I hadn’t cooked with tonka beans before so I’ve been experimenting with them, grating them like nutmeg and adding them to rice custard and fruit sauces. They seem to have an affinity for plums, so 1 grated one bean into the jam.
Tonka beans are black, wrinkly lozenge-shaped seeds that come from a South American tree. Mine measured ¾-1 inch long. They have an exotic aroma, vaguely like vanilla, chestnuts, and almonds, but also a deep spiciness not unlike cinnamon. While used extensively elsewhere in the world, tonka beans are frowned upon in the U.S. because they contain the anti-coagulant coumarin, which can be toxic in large doses (but is used medicinally to treat stroke survivors). Grating a little in jam can do no harm, however, and there appear to be plenty of recipes as well as sources for obtaining them.
The result was a rich tasting plum jam with an enticing hint of perfumed beans.
Plum Jam with Tonka Bean
16 plums (1 lb 12 oz before pitting, 1 ½ lb and 4 c cut in ½ inch pieces)
¾ c water
3 c sugar
1 tonka bean, finely grated
Place the cut plums in a wide saucepan and add water. Bring to a boil, reduce to a simmer and cook for about 20 minutes, or until the skin and flesh are very soft. Add the sugar, stirring to dissolve, bring to a boil and cook until the gel point is reached, testing it on a cold plate. Stir in the grated tonka bean.
Ladle into hot jars prepared for water bath canning, and process for 10 minutes after the water returns to a boil. Turn off the heat, remove the lid from the canner and let sit for 5 minutes before removing the jars to sit undisturbed until cool.
Makes about four 8-oz jars.