How To Sterilise and Seal Glass Jars (2024)

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.

How To Sterilise and Seal Glass Jars (1)

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.

How To Sterilise and Seal Glass Jars (2)

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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How To Sterilise and Seal Glass Jars (2024)

FAQs

How To Sterilise and Seal Glass Jars? ›

Basic process for sterilising jars

How long do glass jars need to be sterilized? ›

Wash the jars, lids and bands in hot, soapy water; rinse well. Put the jars on a rack in a pot of water. Boil 10 minutes, then reduce the heat and simmer until ready to use. Meanwhile, put the lids and bands in a separate saucepan of simmering water until ready to use (do not boil).

How do you boil and sterilize glass jars? ›

Bring the water to a boil. Start a timer and let it boil for 10 minutes, make sure the jars remind submerged in the water throughout this time. Remove jars and caps from the pot. The jars and caps are now sterilized and ready to fill.

How long do you boil jars to seal them? ›

Bring to a rolling boil, cover the canner and boil for 10 minutes if using 4-, 8- or 12-ounce jars or for 15 minutes if using 16-ounce jars. (Check individual preserve recipes for more specific processing times.) Let cool for 10 minutes before removing the jars from the pot.

How to seal glass jars at home? ›

Mason jars are made for canning food. You don't want that food to spoil. You seal the jar by sterilizing the jar, and by putting hot food in it and putting the seal on, then screw the lid on. As the contents cool, the air inside will contract causing the lid to seal tight.

How to make jars airtight? ›

- Use a mason jar and ring lid. The ring lid forms a good seal that pulls down tight under suction pressure to close the jar. - Use a jar with a screw-top lid fitted with an elastomeric or rubber seal ring around the lip. When you screw on the ring, it compresses to form an airtight seal.

What happens if you don't sterilize canning jars? ›

Dirty or jars not correctly cleaned will infect the food inside, and it will spoil very quickly. Sterilizing is a quick and easy process so therefore should never be omitted. Here are simple ways to achieve proper sterilization and make all your efforts at jam making, bottling and canning a success.

How to seal jam jars without a canner? ›

Open-kettle canning involves boiling preserves in an uncovered pot until they reach their setting point, putting the jam into jars and allowing the jam's heat to form the vacuum seal. Wynne turns the jars upside down to sterilize the interior of the lid.

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