How To

How to sterilise and seal glass jars

Love the idea of making your own jam and chutneys for loved ones? Check out our step-by-step guide to storing homemade jams, marmalades, and preserves the hygienic way.

Jams, marmalades and preserves should be added to sterilised jars and sealed while still hot. Your glass storage jars must be without chips or cracks. Just before use, they need to be sterilised and dried, using clean hands. Hygiene is important so use clean tea-towels when holding or moving the jars.

To sterilise jars

  • Place the cleaned jars on their sides in a large boiler or saucepan; cover with cold water.

  • Cover the pan and bring to the boil over high heat; boil for 20 minutes.

  • Carefully remove jars from water; drain.

  • Stand, top-side up, on a wooden board. The heat from the jars will cause any remaining water to evaporate quickly.

  • Stand the clean jars, top-side up, on a wooden board placed in a cold oven (do not allow the jars to touch); heat oven temperature to very slow (120°C/100°C fan-forced), then leave the jars in the oven for 30 minutes.

passionfruit andtomatojam

Try this sweet but savoury passionfruit and tomato jam recipe.

To seal jars

As soon as the preserves are spooned or poured into the sterilised jars or bottles, they must be correctly sealed to prevent deterioration. Fill the hot dry jars right to the top – preserves shrink slightly on cooling and a full jar means less trapped condensation. Seal the jars while still hot. This rule applies to all jams, jellies, pickles and chutneys.

Which lid do I use?

  • Metal lids are not suitable unless they have a protective plastic insert or liner to prevent corrosion.

  • Plastic screw-top lids give a good seal (plastic snap-on lids are not airtight enough). Plastic lids must be well washed, rinsed and dried, or put through the dishwasher.

  • Some older preserving outfits have glass lids; these can be sterilised in the same way as the jars.

  • Do not use aluminium foil, cellophane or paper covers for preserves; acid in the preserves will corrode foil, while paper and cellophane are not airtight enough for long-term keeping.


This peach and passionfruit jam makes the perfect heartfelt gift.

Paraffin wax

To seal jars the old-fashioned way with paraffin wax (available from chemists):

  • Melt wax slowly in a small saucepan over low heat. It is important not to overheat the wax or it will shrink on cooling, giving an imperfect seal.

  • Pour a thin layer over the top of the cooled preserve, about 2mm thick, just enough to cover the surface. Leave until almost set, then pour another thin layer on top of the first layer.

  • Insert small pieces of string in the wax just before it sets to make it easier to remove wax.

Where can I find a “cool dark place”?

Most modern homes have heating in every room, so if a recipe tells you to “store in a cool dark place” consider the garage, cellar or under the house where it’s cool and the temperature is constant. If you live in a wet or humid climate, then use the refrigerator.

For some brilliant jams, conserves and chutney recipes, check these out:

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