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Plum Jam
The directions for making various kinds of plum jam are given under the name of the plum itself. There are so many varieties of this fruit, and these differ so much in quality and sweetness, that hardly any general recipe can be given. Nevertheless, as there are numerous occasions, especially in towns, where fruit is bought without its distinctive name being known, the following instructions are given, as they will answer for most kinds of the fruit. It must be remembered that when the plums are very hard and sour a large proportion of sugar will be required. Divide the plums, and take out the stones; or, if preferred, merely gash them with a silver knife, and remove the stones as they rise in the pan. Spread the plums out on large dishes, sprinkle over them three pounds of sugar to every four pounds of fruit, and let them remain for twenty-four hours. Put them into a preserving-pan, and bring them gently to a boil, stirring them with a wooden spoon to keep them from burning. Carefully remove the scum as it rises, afterwards boil the plums quickly for a quarter of an hour. If liked, a few of the stones can be cracked, and the kernels peeled and added to the jam two or three minutes before the jam is taken from the fire. When the jam sets and the plums are tender, the preparation is sufficiently boiled.
A general-purpose plum jam from a book that otherwise sorts its preserves by variety. The method is sound and still works; the points below cover the vessels, the ratio and the one optional step worth skipping.
- The kernelsPlum, damson and apricot kernels contain amygdalin, which releases hydrogen cyanide when the kernel is crushed or chewed. The Victorian habit of adding a few for their almond flavour is best left in the past; leave them out, and use a drop of almond extract if you want that note.
- Sugar ratioThree pounds of sugar to four of fruit is 75 per cent by weight, on the low side for a long-keeping jam. Expect a softer set and a shorter shelf life than a 1:1 preserve, and refrigerate after opening. Very sour or hard plums, as the book says, will take more.
- The preserving-panThis meant a wide, shallow, heavy pan — traditionally unlined brass or copper — whose broad surface drives off water fast. A wide heavy-based stainless pan does the same job. A tall stockpot does not; the jam will stew rather than reduce.
- The silver knifeSilver was specified because iron and steel blades of the period reacted with fruit acids and discoloured the flesh. Modern stainless steel is fine.
- The 24-hour macerationNot idleness. Standing the fruit in sugar draws out juice, dissolves the sugar before heating and helps the plum halves keep their shape rather than collapsing. Cover and leave in a cool place, or the refrigerator in warm weather.
- Judging the setA quarter of an hour at a rolling boil is a guide, not a rule; time depends on the width of your pan and the ripeness of the fruit. Plums are reasonably high in pectin, particularly when slightly underripe. Test at 220F/105C on a sugar thermometer, or with the cold-saucer wrinkle test.
- SkimmingScum is trapped air and protein, not spoilage. Skim it while the jam comes gently to the boil, before the fast boil starts; a very small knob of butter stirred in at the end disperses whatever remains.
- Jars and yieldFour pounds of fruit with three of sugar gives roughly five to six pounds of jam, so about five or six 1 lb jars, less if the plums are stoned before weighing. Fill hot jars with hot jam to within a quarter-inch of the rim and seal at once, or process the filled jars in a boiling-water bath by current guidance.
The book declines to give a single plum jam recipe because in the nineteenth century plums were sold by name and treated as distinct preserves, with directions given under the name of the plum itself. What this page records is the effect of the towns on cookery — a household buying fruit from a barrow or a market stall often had no idea what variety was in the basket, and needed a method that would answer for whatever turned up. British sugar duties were finally repealed in 1874, and cheaper refined sugar made home jam-making more widely affordable. The kernel trick, adding a few peeled stones for an almond flavour, is an old preserving habit shared with apricot and cherry work, and is one of the few Victorian practices that later food-safety knowledge has firmly overturned.