Jam and Preserves Calculator

Sugar, lemon juice and cooking time for jam, marmalade and fruit paste from the weight of your fruit.

Plan your jam

Fruit

Weight of prepared fruit

Weigh the fruit after washing, hulling, peeling and stoning.

Sweetness

Enter a fruit weight greater than zero.

ml lemon juice · % sugar compared with the fruit weight

All figures are approximate. Taste, fruit ripeness and your pan change the result.

A jam thermometer reads 104–105 °C (219–221 °F).
Wrinkle test: chill a saucer in the freezer, put a teaspoon of jam on it and wait a minute. Push it with a finger. If the surface wrinkles, it is set.
Take the pan off the heat while you test, so the jam does not overcook.
If it is still runny, boil for 3–5 minutes more and test again.
Skim the foam and let the jam rest for 5 minutes before you fill the jars.

Wash jars and lids, then sterilise them: boil for 10 minutes, or heat the jars in an oven at 120 °C for 15 minutes.
Fill hot jam into hot jars, leaving about 5 mm at the top. Wipe the rims and close the lids.
For long storage, process the closed jars in a boiling water bath for 10 minutes.
When cool, the lid should not flex. Store the jars in a cool, dark place.
Refrigerate opened jars and use them within about a month.
Low-sugar jam keeps for a shorter time. Store it in the fridge.

Sugar helps jam set and keep. Cutting it a lot gives a softer jam with a shorter shelf life.
Use a wide pan so the water evaporates quickly, and stir often near the end to prevent sticking.
Underripe fruit has more pectin. A mix of ripe and slightly underripe fruit sets best.
Label each jar with the fruit and the date.

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