How to Sterilise Glass Jam Jars Four Ways

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Today let me show you how to sterilise glass jam jars in four different ways – in the microwave, in the oven, in an aga, and in the dishwasher.

I love pickling and preserving fruit and vegetables, and making delicious jams and marmalade. However, I find I frequently have to rummage through old recipes to remind myself of how to sterilise jam jars correctly.

So partly to help myself, and partly to help any readers also a bit stumped by sterilisation, I’ve put together this quick and easy guide. It shows you exactly how to sterilise glass jam jars in the oven, microwave, dishwasher, and aga. Something to suit all preferences, if you will!

Why Do You Need to Sterilise Jam Jars?

Sterilising jam jars is a really important part of the jam, preserve, and pickle-making process. For a start, there is a risk of botulism if you don’t sterilise your jars correctly. 

Secondly, your preserves will last longer. With proper sterilisation, your preserves will last for up to a year as the sterilising process removes any bacteria, yeast, or other organisms that may be lurking in your jar. This means these organisms are less likely to grow and spoil your hard work before you have a chance to eat your jam. Therefore, don’t be tempted to skip over the sterilisation stage!

Jars of strawberry jam with a blue text box that reads how to sterilise glass jars for jam and preserves four ways.

How To Sterilise Jam Jars In Any Situation

Here are my failsafe four methods to sterilise jars, whatever your situation:

In the Oven

To sterilise your jam jars in the oven:

1. Heat your oven to 140°C /  275°F / Gas Mark 1.

2. Wash your jars and lids in warm soapy water. Next, rinse well to ensure no traces of soap. Do not dry your jars.

3. Place a piece of baking paper on a baking tray and place your wet jars on it. Ensure the jars aren’t touching each other.

4. Place in the oven and heat for twenty minutes.

5. Whilst the jars are in the oven, place your wet lids in a saucepan of water, and boil for twenty minutes.

6. That’s you done! If your jam/pickle/preserve hasn’t finished cooking once the twenty minutes are up, keep your jars in the oven with the door closed. I would also keep the lids in the saucepan of water. Cold jars will crack or shatter if you put hot food/liquid in them so you want to keep them warm.

Please note, that to sterilise Kilner jars with rubber seals, it’s best to remove the rubber seal and boil the seal in water. This is because rubber doesn’t tend to react well to being dried in hot air. The jar (minus the rubber seal) can be placed in the oven with no problem.

In The Microwave

This method of sterilising jars in the microwave is a good quick trick to have up your sleeve. Particularly if you find that you’ve used up all of your jars that you sterilised in the oven and still have jam/pickle/preserve waiting to be jarred! Just don’t put metal lids or jars with metal clasps in your microwave. That would be very bad!

If you’re recycling old jars, make sure you’ve removed any labels that might have had any kind of metallic paint/ink on them too. Here’s my guide to removing labels from glass jars in case any are particularly stubborn.

Now that we’ve gotten the safety stuff out of the way, the quickest way to sterilise jars in the microwave is to wash your jar in hot soapy water and rinse it as before. Then place your wet jar in the microwave on full power for about 45 seconds (or until bone dry). Once it’s done in the microwave, make sure you fill the jar whilst it is still hot.

If you’re in a proverbial pickle and need to sterilise metal lids quickly, don’t worry. Even just washing them in warm soapy water and then placing them in a bowl of boiling water while you microwave your jars quickly is sufficient.

In The Dishwasher

To sterilise jam jars in your dishwasher simply put your dishwasher on at its maximum temperature. My dishwasher has a top heat of 70°C. Then allow it to run through a full wash and dry cycle so that the jars and lids are bone dry and still hot when you take them out. Here’s my guide to plastic-free dishwasher detergent in case it’s of interest!

Sterilising jars in a dishwasher does take a bit of planning though, so be warned! Bearing in mind that the jars have to be warm and bone dry when you jar up your preserve, you have to know exactly how long it takes for your dishwasher to complete a whole wash and dry cycle. I personally prefer the oven method, as it takes less planning.

In An Aga

I don’t have an Aga. However, I have it on good authority from a friend who does that to sterilise jars in an Aga simply wash your jars in warm soapy water and rinse clean. Again, don’t dry them – instead place the jars in the simmering oven of your Aga for twenty minutes, in the same manner as you would the oven. Again, make sure you fill your jars whilst they are still hot.

Other Sterilising Points to Bear In Mind

There are a few other pointers to bear in mind when sterilising jars.

  • Firstly, check your jam jars for any cracks or nicks before you start. If you find any then put these jars in your glass recycling. The high temperatures involved in sterilisation could cause them to smash or shatter.
  • Sterilisation liquid or tablets are fine for sterilising jars intended for pickles or chutneys, or anything else strongly flavoured. However, I would avoid them if you’re making delicately flavoured jams.
  • Any lids that are a bit rusty-looking should be put in your metal recycling.

I hope you’ve found this sterilisation guide useful! If there are any hints or tips I’ve missed out on, or if you do things differently then do share in the comments below!

PS: here are some preserve recipes you might like: easy organic marmalade and quick pickled cucumber with fennel flowers. I’ve also pinned this delicious-sounding recipe for the plum season this year. You might like it too!

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