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 hopefully 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
  • FruitExpert
    Re: Pear Trees
    None - Your Question:My pear tree starts with a lot of small fruit, but very quickly they turn blackand dries up?
    24 May 2017
  • None
    Re: Pear Trees
    My pear tree starts with a lot of small fruit, but very quickly they turn black and dries up?
    23 May 2017
  • Gav
    Re: Why do we not hear about Winberries?
    Wimberries are really common around bolton and chorley and many people collect them for pies in summer. And in…
    22 May 2017
  • Chief
    Re: Pear Trees
    I brought a pear tree,it blossomed now all the buds have fell off,any ideas
    20 May 2017
  • Rentam
    Re: Cherry Trees
    Last year my tree had a lot of sap on the trunk (clear jelly) and very few leaves in the summer. This spring it has had wonderful blossom and sap on…
    19 May 2017
  • FruitExpert
    Re: Cherry Trees
    Dr Turab Syed - Your Question:I have two trees in garden which blossom in spring ( cherry blossom) like whole Milton Keynes is turned out in blossom. T
    17 May 2017
  • Maga
    Re: Growing Grapes
    Can I plant grape vine in Enugu state Nigeria and if I can please tell me how I will do it
    17 May 2017
  • Blackie
    Re: Pear Trees
    Hi my conference mini pear tree is in a large plant pot it blossoms brilliant get plenty of pepears on but they all drop off and the leafs go black and…
    14 May 2017
  • Jane
    Re: Pear Trees
    Hi ,someone above asked about Harvest Green pear tree ..I have just purchased one from Homebase for £14 plus ,am gonna prepare ground then plant it My…
    14 May 2017
  • Dr Turab Syed
    Re: Cherry Trees
    I have two trees in garden which blossom in spring ( cherry blossom) like whole Milton Keynes is turned out in blossom. Then they have yellow fruit…
    13 May 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.