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Jams
Jams are usually made with small fruits or with chopped large fruits. Cook slowly with an equal weight of sugar until thick; put into sterilized tumblers or small jars and seal.
This is a method rather than a recipe: equal weights of fruit and sugar, cooked down, potted hot. The proportions still work, but the sealing instructions predate modern canning practice.
- Equal weights, not volumes"An equal weight of sugar" means you weigh the prepared fruit after hulling, pitting or chopping, then match it gram for gram. A pound of fruit with a pound of sugar gives roughly two to two and a half cups of finished jam.
- TumblersA tumbler is a straight-sided drinking glass, once the standard jam container, sealed with a disc of melted paraffin poured on top. Paraffin seals are no longer recommended because they shrink and crack, letting mould in. Use standard canning jars with two-piece lids.
- Sealing"Put into sterilized tumblers or small jars and seal" is open-kettle canning, which relies on the heat of the jam alone. Current practice is to fill hot jars to a quarter inch of the rim and process them in a boiling water bath for ten minutes, which drives out air and makes a reliable seal far more likely.
- Cook slowly, but not too longModern jam-making generally uses a steady boil in a wide, heavy pan rather than a long simmer, though the original says only to cook slowly. Prolonged boiling degrades the fruit's natural pectin and darkens the sugar; small-fruit jams often reach setting point within fifteen to twenty-five minutes of hard boiling.
- Judging "until thick"The original gives no test. Setting point is 220F at sea level, about 8F above the boiling point of water where you live. Failing a thermometer, a spoonful chilled on a cold saucer should wrinkle when pushed with a finger.
- Which fruits this suitsThe original names no fruits, only "small fruits or chopped large fruits". Currants, gooseberries and plums carry enough acid and pectin to set on their own; strawberries (acidic but low in pectin), sweet cherries and peaches are more likely to stay syrupy unless you add lemon juice or combine them with a high-pectin fruit.
- Scum and skimmingFoam rises as the fruit boils; skim it off near the end or stir in a small knob of butter to disperse it. Left in, it sets as a cloudy layer at the top of the jar.
Jam in the sense used here — fruit crushed or chopped and boiled with its own weight of sugar — became a household staple largely after refined sugar got cheap in the nineteenth century; earlier fruit preserves were closer to confectionery, expensive enough to be served as a sweetmeat rather than spread on bread. The equal-weight rule is not arbitrary: sugar at roughly 60 percent of the finished weight binds enough water that mould and yeast cannot easily grow, which is why these preserves kept in a cool larder. The tumblers it mentions were the ordinary glasses of the period, sealed with paraffin wax, a practice that persisted in American kitchens well into the mid-twentieth century before agricultural extension services steered home canners toward processed jars.