How Canning Jar Lids Work Canning jar lids work by forming a vacuum seal during processing. The sealing compound on the lid sits against the jar and forms the all-important seal with the screw band holding it in place.
As the food in the jar is boiling during processing, oxygen is pushed out of the jar. As the food cools the lid will be sucked down and the rubber seal will form a tight seal keeping out air and protecting the food from any further contamination until the lid is removed. Standard canning lids are not reusable. The screw band part can be used over and over but the flat lid is a one-time use. After use the sealing compound will become indented which might interfere with a new seal.
Take a flat lid that has not been used and one that has and compare them. Look at the inside of the lids where the sealing compound is. You’ll notice that after it has been used it will show an indentation where it sealed to your jar. This indentation flattens the sealing compound and it may not seal the second time around.
Standard Canning Lids The 2 piece canning jar lids that the USDA recommends consist of a screw band and a flat lid. The flat lid has a sealing compound on the inside rim. I’ve also heard them called ‘dome lids’, ‘flats’ or ‘seals’. These can be purchased as a set of both parts or you can just purchase the flat lids. They are sold in individual boxes of 12.
Canning Lids in Bulk And now you have choices! I started purchasing canning lids in bulk a few years ago. I know I’ll use hundreds of lids so instead of individual boxes I love getting my lids all at once in the sleeves that Lehman’s supplies.
Not only does it save on waste (all those boxes to toss away) it also saves on trips to the store. Often I’d be at the supermarket or mega store to purchase lids in August… and they would be gone! I asked the store clerk once why they don’t stock more, her response was that canning season was almost over. Um… really?! We didn’t even get to apple season yet!
Reusable Canning Lids And yet even more choices. Reusable caning lids. I love this product. They have actually been around for many years. I had just not heard of them before this last year.
There are 2 parts to this lid. The flat and the rubber gasket which makes the seal. Use them with standard canning rings just as you would regular flats. Except….. you don’t buy new every year!
These lids are reusable over and over. They are dishwasher safe and I must say I was pleased at the reasonable cost. For an item that you don’t need to repurchase you will save money after only a few uses. Plan ahed, so you’re ready when the harvests start to come in! I’m stocking up now.