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Raspberry and Cherry Jam
Put eight pounds of raspberries into a preserving-pan with four pounds of stoned cherries and boil them for fifteen minutes. Remove the scum, if any has gathered, and add nine pounds of sugar. Boil again for about an hour or until the jam hangs from the spoon, skim it again, pour it into pots, cover them when cold, and they will be ready for use.
A hotel-scale preserve: twelve pounds of fruit to nine of sugar, which will fill a domestic stockpot to the brim. The one thing to change is the hour of boiling.
- Scale it down firstAs written this yields roughly 13-14 lb of jam, which will fill a great many half-pint jars. A quarter batch (2 lb raspberries, 1 lb stoned cherries, 2 lb 4 oz sugar) behaves far better in a home pan.
- The preserving-panA preserving-pan is wide, shallow and unlined copper or heavy brass, chosen for fast evaporation rather than depth. Use the widest heavy-bottomed non-reactive pot you own; a tall stockpot traps steam and lengthens the boiling considerably, which is how jam overcooks.
- An hour is too longModern practice cooks jam to a temperature, not a clock. Set point is 220F (105C) at sea level, or the wrinkle test on a chilled saucer. With this much sugar and fruit that will likely arrive well short of an hour, and boiling past it dulls the raspberry flavour and darkens the colour.
- "Hangs from the spoon"The sheet test: lift a cold metal spoon from the pan and the last of the jam should slide off in a single sheet rather than two separate drips. It is a reliable indicator, but a thermometer is quicker and less dependent on the spoon.
- Pectin balanceCherries are low in pectin; raspberries carry more, and plenty of acid with it, so the two together set better than cherries would alone. If your cherries are very ripe, the juice of a lemon added with the sugar will help the set without being tasted.
- Stoning the cherriesSour cherries (Morello, Montmorency) suit this better than sweet varieties, though the recipe does not say which. Pit them over the pan so the juice is not lost; a hand pitter handles a pound in a few minutes.
- SkimmingSkim after the fruit's first boil and again off the heat at the end, when the foam gathers and firms. A small knob of butter stirred in at the finish disperses most of the scum, though it slightly shortens keeping time.
- Sealing'Cover them when cold' refers to the old wax-and-paper style of cover, which is no longer considered a sound seal. Either process filled half-pint jars in a boiling water bath for 10 minutes following current tested directions, or skip the canning and keep the jam in the refrigerator.
Oscar Tschirky's 1896 book collects the working repertoire of a large hotel kitchen, and it includes a preserving chapter. Batches of eight and four pounds are institutional quantities. Mixing two fruits in one pot is a common approach, and the pairing here is practical rather than sentimental: cherries alone set poorly, so they are carried by raspberries, which bring a useful measure of pectin and acid. The nine pounds of sugar against twelve of fruit sits near the traditional three-quarters ratio that was understood, long before the chemistry was described, to be the point at which a preserve keeps.