Jars, rings, and lids (and why you never reuse the flat lids)
People show up to canning with a vague sense that "canning jars" are a single category. They are, but there are pieces inside that category you need to tell apart.
There are three parts to what people just call "a jar." The jar itself. The ring, that metal band that screws on. And the flat lid, the flat disc with the rubbery seal ring on the underside. Three parts, three different rules for reuse, and this is the lesson where I get a little firm with you.
The jar
Regular canning jars, ball or kerr or whatever's on sale, reuse basically forever as long as there's no crack or chip. Run your finger around the rim before every use, especially the rim, because a tiny chip there is exactly where a seal will fail. Find one, that jar's done for canning. Use it for leftovers in the fridge instead, it's not garbage, it just can't be trusted to seal.
You do not need to buy new jars every year. Check garage sales, check your grandma's basement, check the thrift store shelf. Jars are jars.
The ring
Rings are also reusable for years. Their whole job is to hold the lid down while the seal forms, and once the jar's sealed the ring isn't even doing anything anymore, the vacuum is what holds that lid on. I mention it because it matters for how you tighten, which I'll get to in a second.
Rings do rust, especially with our water up here. Hard water leaves mineral spots, and if a ring gets rusty and rough it's a pain to get off later, or it can seize onto the jar. So dry them well after washing and don't store them wet in a drawer.
The flat lid: the one thing I'm firm about
Here's my opinion for today, and I won't soften it. Don't reuse the flat lids. Ever. Rings, yes, forever. Lids, no, one use and done.
The lid has that thin rubbery compound around the edge, and its whole job is to make one good seal, one time. Once it's compressed against a jar rim and done its job, it's spent. It won't reseal reliably a second time even if it looks fine. People try to save fifty cents a lid, and I get it, I'm cheap too, but you're risking a whole jar of jam over fifty cents. Not worth it. Buy a fresh box of lids every canning season, they're cheap, and don't sweat it.
This is also my one hoarding confession. I now buy lids in March, before the shortages hit in August when everyone else remembers they want to can. Brett's stopped commenting on the shelf of lid boxes in the pantry. That's its own story for another day.
Prepping them before you use them
Before you fill jars, wash everything in hot soapy water, jars, rings, and lids. Rinse well, our water leaves spots and residue if you don't. You do not need to sterilize the jars separately if you're processing for 10 minutes or more in the canner, the boiling water does that work for you. I used to sterilize everything in a separate pot first, an extra hour I didn't need. Old recipes tell you to do it out of habit more than necessity.
The lids, though, some manufacturers still say to warm them in hot water before using, not boiling, just hot, so the seal compound softens a little. Check the box. It's a small step and it doesn't hurt anything.
Putting it together, and the part everyone rushes
Fill your jar, leaving the headspace the recipe tells you to. Wipe the rim. I mean it, every single time, wipe the rim with a clean damp cloth before the lid goes on. One drop of jam or brine on that rim and your seal can fail, and this is the step people skip because it feels like a formality. It isn't. It's the step that matters most.
Then the lid goes on, then the ring, and here's the tightening advice: fingertip tight. Not cranked down. Air has to be able to escape from the jar during processing, and if the ring's too tight it can't, and you end up with jars that won't seal properly and no idea why. I over-tightened rings my whole first year because it felt safer, more sealed somehow, and I had a summer of mystery failures until I called the extension office and got straightened out. Fingertip tight. That's it.
A word about the canner itself, since we're near it
Quick safety note while we're on the topic. When you pull jars out of the canner or lift the lid off the pot, the steam rolling out is hotter than the water looks like it should be, and it's the part people don't respect. I reached across a steam vent once, not even near the water, just the steam coming off it, and burned my wrist bad enough that I wore a bracelet to a wedding to hide the mark. The water gets the attention because it's the water, but the steam is the sneaky one. Step back when you lift a lid, let it clear a second, then reach in.
Before next time
Go check what jars and rings you've already got kicking around the house, basement, garage, wherever, and see what shape they're in. If you need lids, grab a box or two, you'll use them.