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Strawberry and Raspberry Jam
Carefully pick over the strawberries and half the quantity of raspberries; put the fruit into a preserving-pan and boil it for quarter of an hour. Skim the fruit and mix with it some coarsely-crushed loaf sugar, using three-fourths of a pound of sugar to every pound of fruit. Boil the mixture for an hour, or until it coats the spoon, stirring it constantly and skimming as often as required. Fill some jam pots with the jam and leave it until cold. Cover the jars with paper the inner side of which has been brushed over with the white of egg. Keep the jam in a dry store-cupboard.
A plain two-fruit jam in the English style, written when sugar came in cones and a paper lid counted as a seal. Two things need attention: the long boil and the covering.
- The seal is the problemPaper brushed with egg white glued down over a cooled jar is not an airtight seal and will not keep jam safely at room temperature. Either treat this as a refrigerator jam and use it within a few weeks, or follow current water-bath canning directions for sterilised jars, hot fill and a measured processing time.
- Loaf sugarLoaf sugar was refined sugar sold in a hard cone and broken up with nippers, which is why the recipe says "coarsely-crushed." Ordinary granulated sugar is the direct replacement, weight for weight.
- Preserving-panA wide, shallow, heavy nonreactive pan — stainless or enamelled. Wide matters more than deep, since evaporation is what sets the jam. Unlined copper or aluminium will react with the fruit acid.
- Fruit proportionsTwo parts strawberries to one part raspberries by weight. The raspberries are doing real work here: they bring more pectin and noticeably more acid than strawberries, which set poorly alone.
- The hour-long boilAn hour of hard boiling after the sugar goes in, on top of the initial quarter hour, will darken the fruit and push it toward caramel. Modern practice combines fruit and sugar early and boils hard for roughly 10 to 25 minutes for this quantity. Judge by the set, not the clock.
- "Coats the spoon"The reliable version of that test is 220F (105C) on a thermometer, or a spoonful chilled on a cold saucer that wrinkles when pushed with a finger. Start testing well before the hour is up.
- SkimmingThe foam is harmless but cloudy. A small knob of butter stirred in near the end collapses most of it and saves repeated skimming.
- YieldThe original gives none. Three pounds of fruit takes two and a quarter pounds of sugar at the recipe's ratio; how many half-pint jars that fills depends on how far the jam is boiled down.
Jam-making of this kind belongs to the English preserving tradition that ran straight through American hotel kitchens in Oscar Tschirky's day — the Waldorf opened in 1893, and a recipe like this one reads as a kitchen standard rather than a novelty. The strawberry-raspberry pairing is practical rather than decorative: strawberries are low in pectin and set badly on their own, and cooks are often said to have propped them up with a more acidic, pectin-rich fruit, a habit predating commercial liquid pectin, which reached American home cooks in the 1910s. The instruction to cover the pots with paper brushed with egg white is older still; the egg white dries to a stiff glaze that grips the rim, and generations of housekeeping manuals recommended it before glass-and-metal canning closures became cheap and common.