How to Sterilise Jars: Oven, Boiling Water, Microwave & Dishwasher

Key Takeaways

• Always sterilise jars before filling with jam, chutney, pickles or sauces, even if they're brand new.

• The oven method is the most reliable: wash the jars, then heat them on a tray at 140°C (120°C fan / gas 1) for 15–20 minutes.

• Treat lids separately. Metal lids and rubber Kilner seals shouldn't go in the oven; boil them or pour boiling water over them instead.

• Fill hot jars with hot contents. Matching temperatures stops jars cracking from thermal shock.

• Need jars for your next batch? Browse our glass food jars and matching lids and closures.

Why Do You Need to Sterilise Jars?

Jars can look spotless and still carry bacteria, yeasts or mould spores. Once you seal food inside, anything left in the jar has weeks or months to grow, which is how a good batch of jam ends up with mould on top or a chutney starts to ferment.

Sterilising kills those microorganisms before you fill. It matters for brand-new jars too: they're packed, palletised, shipped and stored before they reach you, and dust and spores can settle inside at every stage.

How to Sterilise Jars: Methods at a Glance

Method	Temperature / setting	Time	Best for
Oven	140°C (120°C fan / gas 1)	15–20 minutes	Most batches; jars stay hot for filling
Boiling water	Rolling boil, jars fully covered	10 minutes	Small batches, lids and seals
Dishwasher	Hottest cycle	Full cycle	Convenience, when timed to finish as you fill
Microwave	High, jar wet inside	About 1 minute	One or two small jars only, with no metal

Step 1: Wash and Check Your Jars

Whichever method you use, start the same way:

1. Wash the jars and lids in hot, soapy water, or put them through the dishwasher.
2. Rinse well so no soap residue is left behind.
3. Check every jar for chips and cracks, especially around the rim. A chipped rim won't seal properly, and a cracked jar can break when heated. Throw damaged jars away.

How to Sterilise Jars in the Oven

The oven is the method most home cooks and small producers use, because it handles a full tray at once and the jars come out hot and ready to fill.

1. Heat the oven to 140°C (120°C fan / gas mark 1).
2. Stand the washed, still-wet jars upright on a baking tray, leaving a little space between them. Don't put them straight onto the oven shelf.
3. Heat for 15–20 minutes.
4. Leave them in the warm oven until you're ready to fill, then take them out with oven gloves.

Don't put lids or rubber seals in the oven. The lining inside metal lids and the rubber on Kilner-style seals can be damaged by dry heat. Sterilise them in boiling water instead (see below).

How to Sterilise Jars in Boiling Water

1. Place the clean jars in a large, deep pan and fill it with water so the jars are completely covered.
2. Bring to the boil and keep it at a rolling boil for 10 minutes.
3. Lift the jars out with clean tongs and stand them upside down on a clean tea towel or rack to drain.

A folded tea towel in the bottom of the pan stops jars knocking against the base and each other.

How to Sterilise Jars in the Dishwasher

Run the clean jars through the hottest cycle your dishwasher has, with no other items or detergent residue in the machine. Time it so the cycle finishes as your jam or chutney is ready, and fill the jars while they're still warm.

Dishwashers vary, and not all of them get hot enough to sterilise fully. If you're making food to sell, or want to keep it for a long time, the oven or boiling method is the safer choice.

How to Sterilise Jars in the Microwave

The microwave works for one or two small jars when you're in a hurry:

1. Wash the jar and leave it wet inside. A dry jar can overheat.
2. Microwave on high for about 1 minute, until the water inside has boiled away.
3. Remove carefully with oven gloves; the glass will be very hot.

Never put metal lids in the microwave. Microwaves also heat unevenly, so for larger batches stick to the oven or boiling water.

How to Sterilise Lids and Kilner Seals

• Metal twist-off lids: boil for 10 minutes, or place in a heatproof bowl and pour boiling water over them. Leave them in the hot water until you need them.
• Kilner and clip-top jars: remove the rubber seal first. Sterilise the glass jar in the oven, and boil the seal separately for a few minutes.
• Reusing lids: only reuse lids that are undamaged, with the inner lining intact and no rust. If a lid is dented or the lining is lifting, replace it. Our food closures include replacement twist-off lids in common sizes.

How to Sterilise Jars for Jam, Chutney and Pickles

The sterilising method is the same whatever you're making. What changes is how you fill:

• Jam and marmalade: fill hot jars with hot jam, leaving a small gap at the top, and seal straight away.
• Chutney: fill hot jars with hot chutney, pressing down to remove air pockets. Use lids with a vinegar-resistant lining, because acid can corrode bare metal.
• Pickles: sterilise the jars as above. If you're pouring in cold, spiced vinegar, let the jars cool first; hot glass meeting cold liquid can crack.

Choosing jars for a new product? See our guides to choosing the right jam jar and chutney and pickle jars.

Common Mistakes That Crack Jars or Spoil Food

• Thermal shock: pouring hot jam into a cold jar, or cold liquid into a hot one, can crack the glass. Keep the jar and its contents at similar temperatures.
• Putting cold jars into a hot oven: start with jars at room temperature and let them warm up with the oven, or place them in gently.
• Touching the inside: once sterilised, handle jars by the outside only and don't wipe the inside with a tea towel.
• Sterilising too early: jars left open on the side for an hour can pick up contamination again. Sterilise so they're ready just as your food is.
• Using damaged jars or lids: chips, cracks and worn lid linings stop a proper seal forming.

The Bottom Line

Wash, check, then sterilise in the oven at 140°C (120°C fan) for 15–20 minutes. Boil lids and seals separately, and fill hot jars with hot contents. That routine works for jam, chutney, pickles, sauces and preserves, whether you're making a few jars at home or filling hundreds for market.

Sterilising bottles rather than jars? See our guide on how to sterilise glass bottles.

FAQ: What temperature do you sterilise jars at in the oven?

140°C in a conventional oven, 120°C in a fan oven, or gas mark 1, for 15–20 minutes. Higher temperatures aren't needed and increase the risk of cracking.

FAQ: How long do sterilised jars stay sterile?

Not long once they're out in the open. Fill them as soon as possible, ideally while they're still warm from sterilising. If they've been standing for a while, sterilise them again.

FAQ: Do new jars need sterilising?

Yes. New jars may look clean, but they can pick up dust and spores during packing, shipping and storage. Sterilise them before their first use.

FAQ: Can you sterilise jars in the microwave?

Yes, for one or two small jars: wash the jar, leave it wet inside, and heat on high for about a minute. Never microwave metal lids, and use the oven or boiling water for larger batches.

FAQ: Can you reuse jam jar lids?

You can, provided the lid isn't dented or rusty and the inner lining is intact. Sterilise it before reuse. If in doubt, use a new lid, because a poor seal is the most common reason preserves spoil.

Stocking up for your next batch? Shop our glass food jars, including the 375ml round jam jar and hexagonal jars, with matching twist-off lids. Trade packs and pallets are available.