Updated October 2026

How to Make Jam, Jelly and Marmalade That Keeps

Cook to the set, fill hot jars, and give them 5 minutes in boiling water. That last step is the one most Australian recipe books leave out.

Jam keeps in the cupboard because of its sugar and a good seal. Cook the fruit and sugar to about 104.5°C (or until it wrinkles on a cold saucer), fill it hot into sterilised jars with 6 mm of headspace, put the lids on and boil the filled jars for 5 minutes. That short boil is the USDA's tested step for every jam, jelly and marmalade, and it stops moulds that land on the jam while you fill. Pouring hot jam into hot jars and simply screwing on the lids is the traditional Australian way, but it has never been tested.

What makes jam set

Pectin, acid and sugar have to be in balance. Apples, crab apples, gooseberries, quinces and many plums carry enough pectin to set alone. Strawberries, cherries and blueberries carry little, so they need lemon juice and added pectin, or jam setting sugar, which has pectin blended through it. With citrus, the pectin sits in the white pith under the skin, which is why marmalade sets so readily. For jelly made without added pectin, USDA suggests a quarter of the fruit be slightly underripe, since ripe fruit has less pectin.

Sugar is part of the preserving. USDA's advice is plain: do not cut the sugar in a traditional recipe, because too little stops the set and lets yeasts and moulds grow. If you want less sugar, use a recipe written for a reduced-sugar pectin and follow its processing time, which is longer.

Finding the setting point

• Thermometer: about 104.5°C at sea level, which is 4.5°C above the boiling point of water. Drop it about 1°C for every 300 m you live above sea level, so Toowoomba or Canberra cooks set closer to 102.5°C. Check your thermometer in boiling water first.
• Cold saucer: take the pan off the heat, drop a spoonful on a saucer from the freezer and give it a minute. If it wrinkles when pushed, it is ready.
• Spoon test: lift a cold metal spoon out of the boiling jam. Single drops mean keep going. When two drops run together and slide off in a sheet, it has set.

Jars, lids and the 5 minute boil

1. Sterilise the jars by boiling them, right side up and covered with water, for 10 minutes (add a minute for every 300 m above sea level). If you skip this, process the filled jars for 10 minutes instead of 5.
2. Fill hot, leaving 6 mm of space at the top. Wipe the rims with a clean damp cloth.
3. Lid them. USDA's times are for jars with two-piece self-sealing lids. Lug lids from bought jars are common here but were not part of that testing, so new Mason-type lids are the safer choice.
4. Boil the filled jars covered by 2.5 cm of water: 5 minutes up to 300 m, 10 minutes from 301 to 1,800 m.
5. Cool and check. Leave the jars 12 to 24 hours, then press each lid. A lid that flexes has not sealed: keep that jar in the fridge and eat it first.

Wax discs and paraffin seals are no longer recommended, and turning jars upside down is not a substitute for processing them.

Low-sugar, fridge and freezer jams

Jams set with gelatin and sweetened with sugar substitutes are fridge jams: USDA says eat them within a month. Uncooked berry jam made with pectin keeps 3 weeks in the fridge or up to a year in the freezer. Any of these left on the bench will ferment or go mouldy quickly.

Marmalade

Seville oranges come into greengrocers around July and make the classic bitter marmalade, but lemons, limes, cumquats and grapefruit all work. Simmer the shredded peel in water until soft (about 30 minutes) before the sugar goes in; sugar toughens peel that is still firm. Keep some white pith with the peel, because that is where the pectin is, then boil hard to the set and process like jam.

Which fruit, when

Strawberries and early stone fruit start in spring in Queensland and peak in late spring and summer down south. Apricots and plums run through summer, figs and quinces arrive in autumn, and citrus carries marmalade through winter. Grow your own and the strawberry guide is the place to start.

When something goes wrong

• Runny jam: short on pectin or acid, or not cooked to the set. USDA's advice is to remake soft jam in small batches with added pectin, cooking only one batch at a time.
• Rubbery jam: cooked too long or too much pectin. Next time test sooner.
• Crystals: sugar that did not dissolve before the hard boil. Stir until the sugar has gone before you turn the heat up.
• Mould: throw the whole jar out. USDA warns that moulds on jam can carry mycotoxins, so scraping the top off is not safe.

Sources we checked (October 2026): USDA Complete Guide to Home Canning (2015) and So Easy to Preserve (University of Georgia, 6th ed.) through the National Center for Home Food Preservation: General Information on Canning Jams, Jellies and Marmalades, Berry Jams without Pectin, Berry Jam (Uncooked), Citrus Marmalade, Testing Jelly without Added Pectin, Sterilization of Empty Jars; Food Standards Australia New Zealand, Clostridium botulinum.

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