Home > Ask Our Experts > How Do I Ensure Jars are Sealed Properly?

How Do I Ensure Jars are Sealed Properly?

By: Lucy Debenham BA (hons) - Updated: 28 Sep 2012 | comments*Discuss
 
Jam Jar Sterilised Jar Jar Seal Rubber

Q.

I have just bottled some pears and apples in the glass jars with glass tops and rubber rings (my first time I might add) in an electric steriliser machine, how do I know if they have sealed properly, they are still warm and the fruit seems to be towards the top of the jars?

(Mrs Maureen Hill, 16 September 2008)

A.

It is important to sterilise jars, so that bacteria doesn’t have a chance to form on the surface of the jam, causing it to go mouldy. By sterilising the jars beforehand you should avoid this.

One method you can try is checking the seals on the top of the jar by turning them upside down. Obviously, if there are any leaks, they’ll become apparent quite fast! This should let you know whether the jam jars have sealed themselves properly. Hot air expands and rises – this is most likely why all the fruit sits at the top of the jar shortly after being bottled. But as the hot air inside the jar cools, the air contracts and draws in the lid and seal, effectively creating a vacuum. During cooling you’ll probably notice that the fruit begins to settle as the liquid cools.

The vacuum created by the cooling air firmly closes the lid down. A vacuum means that no air can escape and no air can get in. And as the jar has been sterilised, there is no bacteria that can grow within this airtight space. Jars with metal lids have a small ‘button’ that is drawn inwards as the vacuum is created – a useful visual aid to show that the jar has sealed. If this button has popped, the jam jar either has a leak or the jar has been opened. You’ll often see supermarket jams with these pop buttons.

But with glass-lidded jars with rubber seals, of course there’s not a visual ‘thumbs up’ that everything has sealed properly. So in this case, as aforementioned, the best thing to do is very simple. By turning the jar upside down you’ll not only check for leaks, but this is also a great way to store your bottled fruit. By creating a vacuum at the bottom of the jar when stored upside down, there is a much better chance that there will be no gaps or leaks for air to get in. Obviously, this means that no mould will form on the surface of the preserved apples and pears and is a sort of “two pronged attack” on ensuring that the jars are sealed properly.

You might also like...
Share Your Story, Join the Discussion or Seek Advice..
Why not be the first to leave a comment for discussion, ask for advice or share your story...

If you'd like to ask a question one of our experts (workload permitting) or a helpful reader hopfully can help you... We also love comments and interesting stories

Title:
(never shown)
Firstname:
(never shown)
Surname:
(never shown)
Email:
(never shown)
Nickname:
(shown)
Comment:
Validate:
Enter word:
Topics
Latest Comments
  • Welshgrower
    Re: Growing Apricots
    I am really keen to try a Apricot 'Flavourcot'® tree in our front garden, lots of sun but am not sure how it will do in South Wales with the rain…
    27 March 2017
  • LOU
    Re: Apple Trees
    @Ash - it might be a cooking apple or crab apple tree :)
    24 March 2017
  • kunfayo
    Re: Growing Grapes
    Hello. I will like to grow a grapevine at the back of my house in Ogun State Nigeria, West Africa. Is this possible? Where do I start from?…
    24 March 2017
  • FruitExpert
    Re: Cherry Trees
    Leswang - Your Question:My cherry tree has four flowers on it but there are no leafs I thought you need leafs to produce the blossom why has this happe
    24 March 2017
  • Ash
    Re: Apple Trees
    I recently bought a house in UK and there is a apple tree in the garden. The fruit is not sweet and tasty which makes it difficult to consume directly.…
    24 March 2017
  • Leswang
    Re: Cherry Trees
    My cherry tree has four flowers on it but there are no leafs I thought you need leafs to produce the blossom why has this happened
    23 March 2017
  • NickH
    Re: Using Up a Plum Glut
    Hello, i have space in my garden for one plum tree, cannot grow too big due to space restrictions (2m high, not too wide), must…
    22 March 2017
  • MarieR
    Re: Orange Trees
    I'm doing an assignment based on orange juice and I'm hoping you would be able to answer some of the question I have. One of them is how does oranges…
    20 March 2017
  • Clive
    Re: Orange Trees
    I have a citrina miniature orange tree most of the fruit was off the tree when i purchased it there are small buds where the fruit was should these be…
    18 March 2017
  • DevonDigger
    Re: Orange Trees
    @Cath - always tricky to answer questions such as this as like any young seedling it has to gather strength and winter is never the best time to do…
    16 March 2017
Further Reading...
Our Most Popular...
Add to my Yahoo!
Add to Google
Stumble this
Add to Twitter
Add To Facebook
RSS feed
You should seek independent professional advice before acting upon any information on the FruitExpert website. Please read our Disclaimer.