3

When I make a jam, I put it while it's hot into a jar, then close the jar with its lid (a single-piece, screw-on metal lid) and put in cold water. After doing this, I can usually keep the jam outside the refrigerator for months. But, when I try to open the jar, it is very difficult and in many cases I have to use a plyer to fold the lid open.

Is there a way to seal a jam for long-term preservation, such that it can also be opened easily?

EDIT: I just bought a jam at the supermarket. It is canned just like my jams - in a glass jar with a single-piece screw-on metal lid. It can remain on the shelf for months without refrigeration. Opening it is very easy - I just twist the lid slightly and it opens. I don't need to use force or any special tool or technique. The lid remains intact and can be used again. HOW DO THEY DO THIS?

Erel Segal Halevi
  • 677
  • 2
  • 11
  • 21
  • Are you using canning jars with ring and lid? The way you describe it, it sounds like you might not be... – Cascabel Aug 26 '14 at 06:51
  • No, I use a standard jar with only a lid. – Erel Segal Halevi Aug 26 '14 at 07:28
  • Something meant for canning, or reusing a jar from something else? – Cascabel Aug 26 '14 at 07:37
  • This jar: http://www.huberman.co.il/ShowCatalogItem.asp?ID=1514&CatID=150 clean and new (not used before), but not specifically meant for canning. – Erel Segal Halevi Aug 26 '14 at 08:14
  • So it's just the lid from the two-piece ring-and-lid? (it'd be difficult to use pliers to 'fold the lid open' if it was a commercial jar lid. – Joe Aug 26 '14 at 15:17
  • @Joe It looks a lot like a commercial jar, a one-piece screw-on lid. – Cascabel Aug 26 '14 at 16:29
  • I guess they at least have the little pop-up/down bit in the middle, so you can verify that you have an airtight seal? Without that, I'd be worried that you could even get a physically tight seal (the threads are wedged somehow) without it being safe. – Cascabel Aug 26 '14 at 16:31
  • @Jefromi : I only saw the glass portion in the link ... no metal lid. Was it in a subsequent link? (I can't read hebrew, so couldn't dig into it). ... and trying to fold back a commercial lid without breaking the jar in the process would be *much* more effort than just trying to break the seal by twisting) – Joe Aug 26 '14 at 18:04
  • This lid? http://www.huberman.co.il/ShowCatalogItem.asp?ID=123&CatID=150 – Jolenealaska Aug 26 '14 at 20:52
  • @Jolenealaska yes. – Erel Segal Halevi Aug 28 '14 at 09:18
  • A stupid question this late -- but are you using a canning funnel? it not only helps to get the food in there without making a mess -- but also making sure that you don't get stuff on the top of the jar edge or threads, where it might glue down the lid. – Joe Jun 05 '17 at 00:20

3 Answers3

7

You just need to work out your forearms more. :)

If food gets on the rim of the jar it can greatly add to the friction after the lid is on. It actually makes the whole process unreliable- the food might prevent a seal from forming or it might harden and make the lid difficult to remove- either way make sure the rim of the jar is clean.

Canning jars create a vacuum when the heated air in the jar contracts. This vacuum is what holds the lid on tightly. You can alter the strength of the vacuum in two ways: 1- leave more air at the top of the jar (called headspace).
More air means that a smaller percentage of the air will be forced out and the seal will be weaker. Be careful that you don't make it too weak. If the seal fails the food will spoil.
Jam recipes meant for normal canning jars will include the recommended headspace. You should start there with your experiments.

2- Let the jam cool a little before applying the lid.
This will also result in less air being forced out and a weaker seal. This is something you can experiment with but it would be more finicky than #1. If you do try it, watch your jars closely for a while and put them in the fridge if the seal fails.

The canning process for jam in normal canning jars usually includes boiling the jars afterwards to ensure the jars seal properly. With those lids, sealing too strongly isn't a concern as the lids are disposable. Even with your jars, you want a very strong seal. If you are having trouble opening them perhaps you should try using a tool that will give you leverage but not damage the lid.
A Jar Opener

Community
  • 1
Sobachatina
  • 47,417
  • 19
  • 159
  • 254
  • I just bought a jam at the supermarket. It is canned just like my jams - in a glass jar with a single-piece screw-on metal lid. It can remain on the shelf for months without refrigeration. Opening it is very easy - I just twist the lid slightly and it opens. I don't need to use force or any special tool or technique. The lid remains intact and can be reused. HOW DO THEY DO THIS? – Erel Segal Halevi Aug 28 '14 at 09:19
  • 1
    This. I have never had any issues opening jars of my own jam (similar to store-bought ones) as I use a funnel to fill my jars. However, I have found other people’s home-made jams difficult to open at times. Upon closer inspection, they turned out to have bits of jam all around the rim and the threading. Keeping the rim and threading clean is key. I’d still put on the screw cap immediately, as I am worried that letting things cool down while the jar is still open might affect shelf life. – user149408 Dec 08 '22 at 13:25
4

What's always works for me is to run the lid under hot water. Not sure of the scientific principle of this but it works. Maybe the metal expands. Maybe the air molecules that contracted when the jam cooled and created a vacuum expand when the air around it is heated reducing the vacuum and thus the seal. Maybe both. Either way it should work.

Catija
  • 16,300
  • 8
  • 54
  • 86
Steph
  • 41
  • 1
  • It's a bit of both. (Steel expands 2 to 3x as much as glass for the same temperature change, and the air expands, too.) It's also possible that it softens the material that's around the edge of the lid to make the seal. – Joe Nov 18 '16 at 20:18
3

From your comments, I'm not 100% sure which style of lid you're using.

For a two-piece ring-and-lid, you just need to lift the lid slightly ... the lid is a disposable item, and you shouldn't reuse it. You just don't want to damage it so much that you can't keep a good seal (while in the fridge) if you don't use the item all at once. For this, I like the two-ended 'churchkey' style bottle/can opener, using the bottle (blunt) side to pry the lip up slightly 'til the seal breaks.

For a commercial-style lid, I hold the jar from the bottom, at about a 30 to 45° angle from completely upside-down, and tap around the edge against either the floor or a heavy wooden cutting board. (a surface with some give, but enough mass to absorb the impact). This can (but won't always) break the seal so you can more easily open the jar.

If neither of these work, you can try putting the lid under running hot water -- some people think it's to soften jam left on the jar lid (and it might do that), but we're actually more interested in heating up the air at the top of the jar ... this will reduce the vacuum pressure from the canning process, and make it easier to open. (although then it's wet and slippery, so you likely want to dry it so you don't drop it in the process).

...

and, when all fails ... for commercial jars, I like channel-lock pliers. For two-piece lids, you use the sharp side of the church key, or an ice pick to release the pressure, then change out the lid for fridge storage.

Joe
  • 78,818
  • 17
  • 154
  • 448
  • 1
    I got a silicone trivet / potholder that I finds gives me pretty good grip for one-piece jar lids. (before I go to the channel locks) – Joe Nov 18 '16 at 20:20