rolyateel said:I am using the two piece lids which are the only type I can find in the UK. They are expensive at around 2.00 pounds per jar. So if these single lid jars defiantly work, I will look into shipping a batch to the UK
I would give it a shot since they are not only approved by several European countries, its whole system seem to work as safe as the two piece lids. Then, jars and lids are usually 0,5 cents at the most. Now that you used a two piece lid, maybe you can try canning a batch of fat with the single lid to see if you notice any difference.
I was at the supermarket today and I checked the expiration date of a glass jar canned tuna with a single lid for curiosity. It said, "preferably to be consumed before 2019". In other words, it is good forever ;)