Everything You Need To Know About Sterilising Jam Jars

When it comes to making home preserves, it’s easy to think that success or failure is purely down to the recipe and that every jam, jelly, pickle or chutney simply needs some fresh ingredients, a good recipe and a little bit of time and patience. In fact, there is another factor in the equation, and that is 100% clean glass jars. 

Sterilisation of your jam jars, sauce bottles and so on is every bit as important as measuring the ingredients properly, getting a good boil and checking for the setting point. Whilst other mistakes might mean that your jam is too runny or too thick, or that it doesn’t taste quite as nice as you’d hoped, by and large, they won’t ruin your entire batch. Get your sterilisation wrong, however, and that’s precisely what could happen. You literally run the risk of having to throw all of your hard work away, if the batch becomes contaminated and goes off.

What Happens If Your Glass Jars Are Not Sterilised

It might be tempting simply to give those jam jars a quick wash in some hot soapy water and then to dry them off with a tea towel before you fill them with your lovely jam. In home preserves, however, that simply isn’t good enough, as it will not sterilise those jars at all and you risk leaving harmful bacteria, moulds, yeasts or micro-organisms on the jars, or on the lids.

Those villains will be delighted when you pour in your amazing strawberry jam or green tomato chutney, as you are simply giving them some food to get to work on! Very quickly, you’ll find that your preserves have spoiled and you may even find mould growing on the top of the preserve - a sure sign that it’s time to bin the entire batch.

The Best Way To Sterilise Glass Jars

Now that we’ve convinced you just how important it is to sterilise your jam jars properly, it’s time to move on and explain how to do it correctly, with the minimum of fuss and bother.

Before you start, make sure that you check all of your jars and bottles over for signs of chips or cracks, and pop any that don’t make the grade in the recycling bin.

One key point to make about sterilising your jars is that you need to do this just a short time before you are ready to use the jars. It’s no good sterilising the jars the night before, or an hour or two before you start to make your jam or chutney, as it’s possible that the jars will then become contaminated again before you use them. You should try to complete the sterilisation process whilst your jam is cooking, so that your jars are still warm when the time comes to fill them.

An ideal way to sterilise glass jars is to use the water bath method. For this, you need a large saucepan. Pop a plate into the saucepan and stand your jars on it. Fill the pan with water, so that the jars are just covered with water and then bring to the boil, keeping the boil going consistently for 10 minutes. Turn off the heat and cover the pan with a lid, so that your jars stay warm until you are ready to pour in the jam. You can do the same for the lids, using a smaller saucepan.

It’s important to take care when it comes to lifting the jars out of the water, as they may still be very hot - always check carefully first or use oven gloves or kitchen tongs.

We mentioned earlier that simply washing your jam jars in hot soapy water wasn’t good enough to fully sterilise jars before using them for home preserves. However, this method can be effective if you ditch the tea towel and instead dry off your jam jars in the oven. Wash them very carefully first, and rinse any soap suds away, then stand each jar on a baking tray and place the tray in a pre-heated oven at 160°C for around 15 minutes.

Again, it’s vital to check for any damaged jars before you start this process, as heating them in the oven could cause chipped or cracked jars to break. And of course, you will still need to sterilise your jam jar lids in a pan of boiling water, as lids typically contain a plastic element, which may melt if you put them in a hot oven.

And really, that’s all there is to it. It’s a step in the home preserving process that often causes confusion or anxiety about getting it right, but with our no-nonsense guide to getting it done quickly and efficiently, there really is nothing to worry about.

Have you been making any jams, jellies or even marmalade recently? If you have been busy preserving, why not share your stories with us on Facebook, Instagram or Twitter?