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Greengage Jam
Choose greengages which are not over-ripe; weigh them, and allow three-quarters of a pound of sugar to every pound of fruit. Remove the stones and skins, and strew over the plums half of the sugar, pounded and sifted. Let them stand for five or six hours. Put them into a preserving-pan, and let them simmer until reduced to pulp; add the remainder of the sugar, and boil until a little of the syrup poured upon a plate feels thick and firm. The jam must be well boiled, as plum jams are apt to ferment. A few minutes before the jam is taken from the fire add a quarter of the kernels, blanched and sliced. Put the jam into jars; put oiled paper over them, and cover the tops of the jars with thin paper, dipped in gum. Probable cost, 8d. per pound. Sufficient, a pint and a half of fruit for one pound of jam.
A straightforward high-sugar plum preserve, written when greengages were a garden staple and jam was sealed with paper rather than lids. Two things need attention: the kernels and the covering.
- The kernelsGreengage stones, like other plum and apricot kernels, contain amygdalin and release hydrogen cyanide when crushed or chewed. The quantity here is small and the practice was ordinary in Victorian preserving, but there is no reason to include them; leave them out, and if you want that faint almond note use a drop of almond extract instead.
- Sugar ratioThree-quarters of a pound of sugar per pound of fruit is about 340 g per 450 g. That is on the low side for long keeping by sugar alone, and the recipe does insist on a hard boil because, as it puts it, plum jams are apt to ferment.
- Skinning the fruitRemoving the skins is optional by modern taste, and the skins can be left on, since they carry pectin and colour. If you do want them off, slit and blanch the halved gages for 30 seconds and slip the skins away.
- The plate test, in numbersSyrup that "feels thick and firm" on a cold plate is setting point, roughly 220F / 105C on a sugar thermometer. Chill two saucers in the freezer first and take the pan off the heat while you test.
- Preserving-panThis means a wide, shallow, heavy pan with plenty of surface for evaporation, not a deep stockpot. Fill it no more than a third; boiling jam climbs.
- "Apt to ferment"What the book calls fermentation is yeast and mould growth in an under-boiled, under-sealed jar. Modern practice covers this with hot sterilised jars, a proper two-piece or lacquered lid, and a 10-minute water-bath process, rather than the oiled paper and gummed paper discs described here.
- MacerationThe five or six hours with half the sugar draws out juice before the fruit is simmered down to pulp. Do it in a covered bowl in the fridge if the kitchen is warm.
- Yield"A pint and a half of fruit for one pound of jam" is a rough volumetric guide: about 2 lb / 900 g of stoned gages takes 1 1/2 lb / 680 g sugar. Expect somewhere between two and three 340 g jars, depending how hard you boil it. Ignore the "8d. per pound" costing entirely.
The greengage is a green-skinned dessert plum, Prunus domestica subsp. italica, and its English name is generally traced to the Gage family of Suffolk, who are said to have grown it in the early eighteenth century after the fruit arrived from France, where it is still the reine-claude. It ripens briefly in late summer and bruises easily, which is why cookery books of Cassell's period give so much space to preserving it, though it was a well-known dessert plum too. The instruction to add a few blanched kernels belongs to an older tradition that treated plum and apricot stones as a free flavouring, the same impulse behind ratafia and noyau; commercial almond essence made the habit unnecessary, and later understanding of the kernels' cyanogenic content made it undesirable.