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You are here: Home / Recipes / Recipes by Course / Easy Jam, Jelly & Preserve Recipes / How to Sterilize Jars For Preserving

How to Sterilize Jars For Preserving

Published on August 26, 2020 by Helen Best-Shaw 4 Comments
Last Updated on July 23, 2021

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Correctly sterilizing your jars, lids and bottles is a vital part of the preserve making process as it will stop the contents spoiling. With a little know how you can confidently, easily and safely sterilize jars time after time.   

Different shapes of empty jam jars with lids, clean, ready to sterilize and fill with jam.

Everything You Need To Know

  • Everything You Need to know to Correctly Sterilize Jars
  • Why Sterilize Jars for Jams, Jellies and Preserves
  • Wash & Check Jars Before Sterilizing  
  • Three Ways To Sterilize Jars for Jam Making 
    • 1 – Sterilizing Jam Jars in Boiling Water 
    • How to Sterilize Jam Jar Lids In Boiling Water
    • 2- Sterilizing Jars in the Oven
    • 3 – Sterilizing Jars in a Microwave Oven
  • How to Avoid Thermal Shock By Warming Sterlized Jars
    • 1 – Warming Jars in the Oven 
    • 2 – Warming Jars in a Dishwasher
    • 3 – Warming Jars in a Microwave 
  • FAQs
  • How to Sterilize Jam Jars for Preserving
    • Instructions
    • Notes

Everything You Need to know to Correctly Sterilize Jars

These guidelines are only for preserves made with sugar and vinegar as the preservative –  Jams, jellies, chutneys and the like.  

Greater precautions are needed for canning fruits and vegetables where the jar contents are not preserved and shelf stable with sugar or acidity.  

Why Sterilize Jars for Jams, Jellies and Preserves

I love to preserve and probably make a small batch of jam or jelly every few weeks – its a relaxing and fun hobby, and it is very satisfying to bring some product home from the market, or friend’s or family member’s garden and make something either for us or to be given away 

Sterilizing the jars for jams, jellies, chutneys, pickles and relishes will remove bacteria and mould spores and stop the contents spoiling.   

After all the effort and expense to make jam, it would be a shame to take a jar from the cupboard and find it has gone mouldy.  At best it is a waste, at worse there could be a bug in your preserve that could make you quite unwell.  

Jars and bottles are easy to sterilise and have ready and warm when you need them.   

Fig jam in a jam jar, waiting for the lid to be put on.

Wash & Check Jars Before Sterilizing  

Before sterilising your jars must be scrupulously clean, with no stuck on food or dust. 

 I put all my empty jars through the dishwasher and check they are clean before they are put away, even so some will slip through with some food stuck on and I nearly always find dust in them, even though they have been stored in a cupboard with their lids on.  

It is vital to check jars for chips and cracks. A chip on the rim will stop the lid sealing and a cracked jar can shatter when you fill it.   I’ve once found a piece of broken glass at the bottom of a brand new jam jar!  Check and then double check! 

Three Ways To Sterilize Jars for Jam Making 

1 – Sterilizing Jam Jars in Boiling Water 

This is the only method recommended for home preservers to fully sterilize jam jars. 

  1. Place a rack at the bottom of a large maslin pan or saucepan. Place the jars on the rack the right way up. 
  2. Completely submerge the jars. Make sure the water is at least 5cm/2″ above the top of the jars. 
  3. Bring the water to the boil, 
  4. Start timing: boil the jars for ten minutes. 
  5. Remove the jars before filling, taking care not to burn yourself. Place them upside down on a clean tea towel to drain.

How to Sterilize Jam Jar Lids In Boiling Water

Jam jar lids in a bowl covered with water. The water was poured in boiling from the kettle to sterilize the lids.

Place lids or rubber seals in a small pan and fill with 4 inches of water, heat and simmer for 10 minutes, turn the heat off and cover the pan until you are ready to seal the jars.

2- Sterilizing Jars in the Oven

A baking tray of jam jars on a shelf in the oven

Sterilizing jars in the oven is not thought to be as effective as using a water bath as above. However, we’ve used this method successfully for several years.

Heat the oven to 160°C 320°F Gas Mark 3. Wash and dry the jars thoroughly. Place in a roasting tray, and then into the oven for 15 minutes.

Remove from the oven and fill immediately, using a jam funnel.

3 – Sterilizing Jars in a Microwave Oven

Again, this is not as effective as using a water bath. Wash and rinse the jars, and do not dry them. Place them, still damp, in the microwave. Microwave on high for 1 minute.

How to Avoid Thermal Shock By Warming Sterlized Jars

It’s very important that glass jam jars are hot before you fill them with boiling jam or chutney. Adding hot jam to a cold jar will result in a thermal shock one or more of your jars will probably break or shatter. There are three easy ways this can be done. 

1 – Warming Jars in the Oven 

Using the oven to warm jars before filling. It’s not recommended as a way of fully sterilizing jars, because unlike submerging jars in water, air is poor at transferring heat.

However, the oven is a handy way to heat jars before filling to avoid thermal shock. 

  1. Place jars in the oven on a baking tray
  2. Set oven to 160C/Gas mark 3. 
  3. Let the oven come up to temperature. By allowing the jars to warm slowly as the oven, the chances of jars breaking from thermal shock are minimized. 

2 – Warming Jars in a Dishwasher

Upside down glass jam jars on the basket on the dishwasher
  1. Place the jars in the dishwasher, open side down. 
  2. Run the dishwasher on a full cycle on it’s hottest setting. This is normally about 70°C/ 160°F
  3. Once the dishwasher has run, fill the hot jars immediately with the freshly made jam. 

This method does require some careful timing: you don’t want the jars to cool before filling them, but a full dishwashing cycle can take longer than it takes to make jam. You might find it useful to time a full cycle of your dishwasher, so that you can start making jam timed to coincide with the machine’s cycle. 

3 – Warming Jars in a Microwave 

If you find that you haven’t prepared enough jam jars for all your preserve, then you can warm a jar in the microwave.

  1. Fill it about one quarter full of water, and place in microwave with a plastic lid on top.
  2. Microwave at full power for 2 minutes (timing may vary according to the power of your machine).
  3. Remove from the microwave, and pour out all the water. Stand the jar upside down on a clean tea towel for a couple of minutes to drain. 
  4. Fill with jam or preserve while the jar is still hot. 

FAQs

Can I reuse jars and lids? 

Advice on this varies, you need to do the research and make a decision.   I reuse jars and lids all the time.  Some people advise new lids every time, others will never reuse a jar. 
The best thing here is good old fashioned common sense.   Generations of jam makers have safely reused jars and lids year after year after year.  Check the lids and discard any that are dented, damaged or rusted.  

What about Kilner style jars? 

Kilner jars with clip on lids are excellent for jams and chutneys, and are very resuable. I find the best way to clean them is to take them apart, removing the metal clip, and wash the jar, lid and rubber seal in the dishwasher.
To remove the clip, the normal way is to pinch the two arms on the lid together. The lid can then be removed. Then remove the clip holding the bottom part of the clip on. Be careful here, because it can ping across the room. Remove the rest of the clip.
Don’t wash the clip in the dishwasher and they are normally made from a mild steel that can rust. Wash in a basin of hot, soapy water, rinse, and dry immediately.
New rubber sealing rings are readily, and cheaply available.

Tried these instructions?If you try this method please tag #FussFreeFlavours on Instagram or Twitter. It is amazing for me when for me when you make one of my recipes or try one of my ways of doing things and I really do love to see them. You can also share it on my Facebook page. Please pin this post to Pinterest too! Thanks for reading Fuss Free Flavours!
9 empty clean jam jars, 2 with lids off, stacked up 2 high.
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How to Sterilize Jam Jars for Preserving

Correctly sterilizing your jars, lids and bottles is a vital part of the preserve making process as it will stop the contents spoiling. With a little know how you can confidently, easily and safely sterilize jars time after time.   
Author: Helen Best-Shaw
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Instructions

Water sterilization

  • To properly sterilize jam jars, place the jars on a rack at the bottom of a large maslin pan or saucepan.
  • Completely submerge the jars. Make sure the water is at least 5cm/2" above the top of the jars.
  • Bring the water to the boil.
  • Once the water is boiling, start timing. Boil the jars for 10 minutes.
  • Remove the jars from the pan with silicone tipped tongs. Empty out the water, and allow to stand upside down to drain completely. Do not dry with a drying up cloth, as that will mean the jars are no longer sterile. Turn the right way up to allow to dry completely, while remaining hot.
  • Fill with jam while still hot.

Sterilizing Jars in the Oven

  • Sterilizing jam jars in the oven is not as effective as using a water bath, as water is a better conductor of heat than air.
  • Wash and rinse jars thoroughly.
  • Heat oven to low: 180°C 350°F Gas Mark 4.
  • Place jars in a roasting dish. Place in the oven for at least 15 minutes.
  • Remove and fill while still hot.

Sterilizing Jars in the Microwave

  • Wash and rinse jars throughly. Do not dry
  • Place in a microwave oven on full power for one minute.
  • Remove and fill while still hot.

How to Sterilize Jam Jar Lids

  • Wash and rinse lids throughly
  • Place lids upside down in a saucepan. This way they won't float. Cover with water
  • Bring to the boil.
  • Simmer gently for 10 minutes.
  • Remove to use; shake off the water, and screw the lid onto the jam jar. Do not dry with a cloth.

Notes

These guidelines are only for preserves made with sugar and vinegar as the preservative –  Jams, jellies, chutneys and the like.  
Greater precautions are needed for canning fruits and vegetables where the jar contents are not preserved and shelf stable with sugar or acidity.  
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    Recipe Rating




  1. Hannah B

    5 stars
    You give some handy and easy to follow information on jam and chutney jars. I do tend to reuse them often, but always find one or two needs extra cleaning or has a crack. All very important and part of the process.

    Reply
  2. Francis

    5 stars
    My first ever attempts at making jam was a total disaster. I made the fatal error of not warming the jars before filling. It was awful. Such good advice on how to prep your jars.

    Reply
  3. Robyn

    5 stars
    I have used the same method for years now, with boiling water. I actually use a fish kettle, as I find they sit perfectly in rows.

    Reply
  4. Steph

    5 stars
    So wise to get things right in jam making. I always reuse my jars so cleaning them is vital.

    Reply

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