3 ways to sterilise jam jars for minimal mould 

Eating jam on toast will solve a sweet tooth – but here's how to clean those jars without getting sour

3 ways to sterilise jam jars for minimal mould

Making jam at home for someone is an expression of love – and it’s delightful until you unveil a thick layer of hairy mould – the result of a bodged jar sterilisation job. That’s when you know you need to learn how to sterilise jars. Sterilising jars for jam making will keep your precious jam safe from bacteria for up to a year.  

Check out our methods so that you can move onto the fun part – making (and eating) it! 

Why sterilising jam jars is essential

First things first, why do we need to know how to sterilise jam jars properly? Well, there are two reasons. One is to do with health. If you don’t take the time to carry out this important step, you increase the risk of bacteria breeding in the jar and producing toxins that can cause dangerous conditions like botulism.[1]

The second reason is about helping your homemade jams and pickles last longer. As the sterilising process helps to remove organisms, bacteria and yeast, they’re less likely to grow in your jars and ruin your tasty creations. Thoroughly sterilised jars give your jam the cleanest, most hygienic environment – so you can enjoy your delicious preserves for longer.[2]


Rather than throwing them away, keeping and repurposing your empty jars and containers is a simple way to reduce household waste. Check out some more tips on living sustainability at home here.

Sterilising jars in microwave ovens

Sterilising jam jars in microwave ovens is really straightforward. Here’s how to sterilise jars in a flash: 

  1. Remove any labels from the jar. Try soaking them in hot soapy water first if they’re tricky to remove. Bonus points to you if you can peel it off in one go. So satisfying.
  2. Use soapy water to make sure that the jar is clean before sterilising. Take care to rinse off all the washing up liquid.
  3. Place in the microwave  (while still wet) and turn on ‘high’ (usually around 1,000 watts) for 30-45 seconds.
  4. Place them upside-down on a piece of absorbent kitchen paper (like Plenty) to dry off.

While sterilising jars in microwave ovens works really well, you can’t sterilise metallic lids in this way. Instead of using the old lids, you can cover the top of the jars with wax (and pretend you live in the 1400s) or buy new lids to seal your jam. 

How to sterilise jars in the oven

Sterilising jars in the oven takes quite a bit longer than in a microwave, but it’s long been known as one of the best methods for sterilising glass jars. You can get the prep done while your jam is simmering and by the time it’s cooked your jars will be ready. Just follow these simple steps:

  1. Set the oven temperature to 130 C or 270 F – no higher, or you run the risk of the glass breaking. And cleaning an oven is hard enough - cleaning an oven full of glass isn't what you need in life. 
  2. Remove the jar labels (by soaking them off, if necessary).
  3. Lay paper in double layers on your oven shelves and arrange the jars (still wet) on the shelves so that they aren’t touching.
  4. Shut the oven and set a timer for 20 minutes.
  5. Use an oven glove to remove the jars and stand them on a heatproof mat to cool enough that they’re safe to handle.

A quick word of caution here: never add hot jam to a cold jar or cold jam to a hot jar, as this can lead to cracking or, worse still, a jammy explosion.

How to sterilise jars in the dishwasher

Sterilising jars in the dishwasher is probably the easiest method, and works really well if you’ve got an extra hot setting on your machine. Sterilising jars for jam making in this way is straightforward with the following steps: 

  1. Make sure the dishwasher is empty and clean.
  2. Remove any labels from the jars (soaking them off if necessary).
  3. Carefully place the empty jars and lids into your machine, ensuring they are secure.
  4. Run the dishwasher on a cycle that coincides with your jam being ready.
  5. Remove the jars one by one and lay on fresh, absorbent piece of Plenty kitchen paper to dry.  
  6. Fill the warm jars with jam and secure with the sterilised lids.

This works well with screw-top and clip-top jars. With clip-top jars it’s best to remove the rubber to make sure that part gets fully sterilised too.


If your jar is tricky to open, add a bit of resistance by placing a strong piece of Plenty kitchen paper over the top of the lid – this should help it twist off more easily.

Now you can take your pick from these three easy ways of sterilising jars for jam making. If you’re making a big batch and have a lot of jars to sterilise, get everyone in the house involved in a jam production line. Maybe start a new business. Get the world talking about your jam. Ok – maybe we’re getting carried away… 

Whether you go for sterilising jars in microwave ovens, your kitchen oven or the dishwasher, each method will help ensure that your jam is safe to eat and longer-lasting too. 

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