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Prune Sauce
Place half a pound of prunes in a saucepan, with a little water, and boil them until they are soft; then remove the stones from the fruit, break them up small in a mortar, and put them in with the fruit, adding a thin strip of lemon-peel, and the strained juice of one lemon, together with sugar to the taste, add a small quality of powdered cinnamon, and one and half wineglassfuls of port wine; let the sauce simmer at the edge of the fire for a few minutes, then rub it through a coarse wire sieve, and serve.
This is a nineteenth-century fruit sauce for roast game, venison or pork, but one line in it puts the whole thing out of bounds: the prune stones are cracked, pounded in a mortar and simmered with the fruit.
- The stones are the problemPrune and plum kernels contain amygdalin, a cyanogenic glycoside. Crushing the kernel and wetting it lets the fruit's own enzymes break it down, releasing hydrogen cyanide along with benzaldehyde, the bitter-almond note that made pounded kernels attractive as a flavouring in the first place.
- The quantity is not trivialHalf a pound of prunes carries roughly two dozen stones. Pounded and simmered, the kernels from that many fruit can put a meaningful quantity of cyanide into a single sauceboat, and straining through a sieve at the end removes the solids but not what has dissolved into the liquid.
- Simmering does not fix it"A few minutes" at the edge of the fire cannot be relied on to drive off the hydrogen cyanide, and gentle heat in the first stage actually favours the enzymatic release. It is the same reason bitter almonds are effectively unavailable at retail in the United States while sweet almonds are not.
- Cooked whole fruit is a different caseWhole stone fruit stewed with the pits intact is not the same hazard: the intact kernel coat keeps the glycoside and the enzyme largely out of contact with the cooking liquid. It is the deliberate crushing that makes this recipe unsafe.
- If you want the dishA prune sauce with port, lemon and cinnamon is a sound idea and worth cooking. Use a current recipe that leaves the stones out altogether.
- On the archaic measuresFor reading the text: a wineglassful of the period is usually reckoned at about two fluid ounces, so "one and a half wineglassfuls" is roughly three fluid ounces, a little over a third of a cup. "The edge of the fire" means the cooler part of the range — a bare simmer.
Sweet-sour fruit sauces for meat are older than the gravies that displaced them, and prunes had a particular hold on European cookery because dried plums travelled and kept when fresh fruit did not; French prunes were traded into northern Europe from the later Middle Ages onward. The instruction to crack and pound the stones belongs to a long tradition of using kernels as a flavouring — the same impulse behind noyau, ratafia and the bitter-almond note in old macaroons and puddings — and some cookbooks went on recommending it into the twentieth century, although the presence of prussic acid in bitter kernels had been known since the early nineteenth century. If the source is Oscar Tschirky's Waldorf cook book of 1896, it is largely a record of what a great American hotel of the period cooked, and sauces of this kind were served with game.