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Plum Marmalade
Stone and peel some ripe plums and lay them in a deep dish and cover them thickly with caster-sugar, place in a cool spot and leave until the following morning. Put them in a preserving-pan with one pound of crushed loaf sugar for every pound of the fruit used, weighting them after they have been stoned, and boil until they are reduced to a pulp; crack some of the stones and boil the kernels in the marmalade, then turn the marmalade into jars and leave it until quite cold. Cover over with paper, and tie down tightly.
A plain Edwardian plum preserve, sound in its sugar ratio but built on two practices that no current preserving guide will endorse: an unmeasured quantity of cracked plum kernels boiled into the fruit, and a paper-and-string closure in place of a sealed jar.
- The kernels are the problemPlum stones enclose a kernel containing amygdalin, which releases hydrogen cyanide when the kernel is crushed and wetted — the same chemistry that makes bitter almonds dangerous. "Crack some of the stones" gives no count, no weight and no relation to batch size, so the dose is entirely unknown. Boiling drives off some of the released gas but does not reliably clear it from a thick, sugary pulp.
- Why cooks did it anywayThe kernels were prized for a faint almond bitterness that flatters plums, and the same trick appears in old damson cheese and apricot jam recipes. Presumably the dose stayed small relative to a large batch, but that is not a margin any modern recipe should rely on, and current preserving guidance omits the step entirely.
- The sealPaper tied down over the jar mouth was the standard Victorian and Edwardian closure, relying on the high sugar concentration of the preserve rather than on an airtight seal. It is not a hermetic seal, and mould on a preserve is no longer treated as something to scrape off. Use a current tested jam recipe with proper jars and processing if you want plum preserve on the shelf.
- Caster and loaf sugarCaster sugar is superfine granulated. Loaf sugar was refined sugar sold in a hard cone and broken up with nippers, then crushed — ordinary granulated sugar will stand in for it. The weighed sugar is a pound to each pound of stoned fruit, on top of the unmeasured caster sugar used for the overnight layering.
- "Marmalade" hereThe older, broader sense of 'marmalade' — any fruit boiled down to a thick pulp rather than specifically a citrus preserve — was still current in recipes of this kind. The instruction to boil 'until they are reduced to a pulp' describes something closer to a stiff plum cheese than a loose jam.
- Preserving-panA wide, shallow, unlined copper or brass pan with sloping sides, designed to evaporate water fast over a large surface. A wide heavy stainless pan is the equivalent; a deep stockpot is not, and will stew the fruit rather than concentrate it.
- The overnight sugaringLayering the peeled, stoned fruit with sugar and leaving it cold overnight draws out juice by osmosis so the pan starts with syrup rather than dry fruit. This is the one step worth carrying into any modern plum preserve.
Oscar Tschirky's book, published under the name of the Waldorf's maitre d'hotel, gathers a large collection of turn-of-the-century recipes, and its preserving chapter reads as English domestic practice transplanted: caster sugar, loaf sugar, a preserving-pan and a paper cover would all have read as unremarkable in a London kitchen of the 1890s. Plums were cheap and abundant in late summer in the northeastern United States, and their pectin and acid made them relatively easy to set without added pectin, which was not commercially available until well into the twentieth century. The kernel trick is old and widely distributed — cooks across Europe added a few cracked stones to plum, damson and apricot preserves for an almond note, the same taste that made ratafia and noyau flavourings popular. Its disappearance from print over the twentieth century tracks the growing understanding of what amygdalin does.