Interactive lesson

Jam and slatko, step by step

Interactive lesson: pectin, sugar and acid, cooking a small batch, setting point, jelly, slatko and the water bath for the jars.

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The whole lesson as text

1. Pectin, sugar and acid

For jam to set, it needs three things in the right balance.

Three things for a set — Pectin from the fruit, enough sugar and enough acid. Without enough acid, jam won't set even with plenty of sugar.
Fruit rich in pectin — Quinces, sharp apples, blackcurrants, redcurrants and gooseberries have plenty of pectin and acid. They are good for mixing with other fruit.
Fruit low in pectin — Strawberries, sweet cherries, peaches, pears and figs have little pectin and acid. They need lemon and pectin, or a mixture with apple.
Lemon per kilogram — For 1 kg of low-acid fruit, add 30 mL (2 tablespoons) of bottled lemon juice or 2 g of citric acid. With figs and pears it is for safety too.

Why: Pectin is the natural “glue” in fruit, sugar binds water, and acid lets the pectin chains join into a network. When one is missing, you get syrup instead of jam, or rubber instead of a soft jelly.

Most of the pectin is in the peel, the cores and in fruit that is not quite ripe. A little underripe fruit in the pan helps.
Sugar is also the main preservative in jam: at 60–65 %, moulds grow with difficulty.

2. Equipment and preparing the fruit

Jam is cooked in small batches, in a wide pan.

A wide pan — A stainless steel or sound enamel pan (a preserving pan), 6–8 L for 2 kg of fruit. No more than 2 kg (4½ lb) of fruit per batch.
Don't double it — Bigger batches set badly. In a tall pan the jam cooks for a long time and darkens.
Tools within reach — Kitchen scales, a sugar thermometer up to 120 °C (250 °F), a wooden spoon and a slotted spoon for skimming the froth.
Wash, prepare, weigh — Wash strawberries with their hulls on and only then hull them, otherwise they soak up water. Dice large fruit and weigh the prepared fruit.

Why: In a wide pan with 1–2 kg of fruit the water evaporates quickly and the jam sets in 10–20 minutes. In a big pan with 6 kg of fruit, cooking takes two or three times as long, the pectin breaks down and the jam darkens.

Don't double a jam recipe. Better to cook three batches one after another.
For raspberry and blackberry jam with fewer seeds, sieve half the fruit.