We want to. We want to reuse canning jar lids. It seems so wasteful to not reuse the lids. It still looks good and it was carefully removed.
This is one of those things that falls into that Camp A and Camp B thing that I discussed a bit in Avoid Common Home Canning Mistakes. Camp A follows the rules and is happy and safe. Camp B is saving a bit of money and is pleased to do so--and argue "my jars seal and no one died." Why is the argument always "no one died"?
What's the job of the lid?
The lid (and not too tight ring) must allow the jars to vent--allow the air that is trapped in the jar out of the jar to create a vacuum of about 20 psi. The sealing compound (the red bit around the edge of the lid), called plastisol, must seal by adhering to the glass jar. And the lid must maintain the vacuum seal for at least one year: keeping air out, keeping microorganisms out, and keeping failures at a minimum. This all sounds pretty damn important so why experiment with a good thing?
A few reasons why canning jar lids shouldn't be reused to can:
- The plastisol is thermoset with the impression left by the jar's rim after heating in a boiling water bath canner or pressure canner--meaning the plastisol now has a "memory" of the rim. So? Well, that impression can inhibit a subsequent good seal, key words, good seal. Take a moment to look at a used lid and an unused lid. As a side note: Indentations in the plastisol from packing and shipping do not affect sealing.
- The plastisol doesn't "bounce back" after being heated again and again. So? Plastisol doesn't simply return to it's previous unused, unheated state to be used like a new lid.
- Plastisol thins when heated over 180 degrees. Where it thins there is less plastisol to create the best seal possible and hold a strong vacuum. It may seal but it will never be as strong a seal as the first time. This is why lids should not be boiled. Lids can be heated to 180 degrees but never, ever boiled! It is fine to process them in a boiling bath canner or pressure canner because the plastisol "wraps" around the jar rim.
- Manufacturers recommend that the lids only be used once. In fact if a seal fails, a new lid should be used to reprocess. Hey, wait, aren't they just saying that to line their pockets with more money? Think of it this way, what happens to plastic wrap after it has been overheated in a microwave? Plastics are designed to have certain properties under specific conditions. So, while it might seem self-serving for Jarden to say the lids are not reusable, the reality is the limitations of the plastisol.
- USDA recommends that the lids only be used once. Yes, you may disagree with government entities and conservative stances but again, it's the limitations of the plastisol.
And lest we forget, botulism is real thing!
Good Canning Lid Practices
- Buy and use new lids for canning.
- Buy lids and mark the box with the month and date. It's a good practice to use lids within a year. Jarden lids (Ball, Kerr, and Bernardin) can be used up to 5 years after manufacture.
- Simply wash, dry, and use Ball and Kerr canning jar lids. You can pre-heat, if you prefer, but never over 180 degrees. Remember do not boil lids!
- What about sterilizing the lids? Lids are sterilized when the canning process is 10 minutes or longer.
- Lids prepared for canning (even if heated to 180 degrees) but not used for canning can be dried and stored for another canning session.
- If a lid fails to seal, do not reuse lid to re-process.
- Don't disturb the lid after processing by tightening the ring.
Remember that the canning jar lids that we typically use in the US (Ball, Kerr, and Bernardin all made by Jarden) save time over the old pre-1968 lids with latex gaskets (Patent Publication Number: US3574147 A). If you are looking to save some money consider buying lids in bulk (BPA-free and made in the USA).
And in case the not reusing guilt is overwhelming you, pass on used lids to friends or for your own dry storage or freezing, garden art project or garden markers, and other cool ideas you can find on pinterest.
Be safe and eat well.