Have you ever gotten your hand on a perfect batch of green beans, decided to can them and spend hours of work dealing with jars and lids, only to have it turn into a big, soggy, cloudy mess?
So have we. So we talked to Robin Seitz, an extension agent with the North Carolina Cooperative Extension, Onslow County Center (and canning guru), about the most common mistakes she’s seen in home canning.
As the go-to guru for canning in Onslow County, Robin fields calls all season long about the problems people face and helps work them through common issues. Here’s her top five canning mistakes based on her years of experience:
1. Processing Low Acid Foods in a Boiling Water Bath
This is the most common error Robin sees. Home canners will use a water bath canner (like this one) and try and can foods with low acid. This is a problem. Not only can you wind up with a soggy, unappetizing mess instead of pristine jars of delicious food, you can actually cause undue harm.
“The temperature (in a water bath) doesn’t get high enough to kill the bacteria you’re trying to kill,” Robin said.
Sure, you may have done it. Sure, it may not have killed you, but that just means you got lucky. Try not to tempt fate again.
2. Getting in a Hurry
If you’ve spent hours — sometimes days or even weeks — canning the latest crop of potatoes from your garden (or your local farmers market), then you’re probably guilty of this one.
Maybe you’ve got to run out and pick up the kids from school. Maybe you’ve got to hand sew a halloween costume. Maybe you’ve promised your church you’ll volunteer for the bake sale. You look at all the time you have left for that pressure canner to cool and you decide to speed up the process, as you’ve got things to do.
So, you take your canner and drop it in an ice bath. Or even put it out on the porch so the wind will cool it down a few minutes faster. What’s the harm?
Plenty. Cooling your product down too fast results in a rapid pressure drop, which messes with the quality of your jars of potatoes (or carrots, or whatever).
“If you don’t let the pressure drop naturally,” Robin said, “You’ll get evaporation.”
That means you’ll lose liquid in the jar and instead of full jars of delicious potatoes, you’ll have some — and sometimes a lot — of your jars suddenly half full of product, exposing your veggies to unwanted air.
While it isn’t a safety issue — pressure canners do a great job of killing bacteria — it means the results will be less than appetizing.
So take your time and work on the sewing projects in between batches. It’ll be worth the effort.
3. Not taking out the air bubbles
There’s a little device that comes with canning tool sets. It’s usually a plastic stick, but it can make all the difference. When dealing with chunky vegetables, large air pockets can get stuck at the bottom of the jars. You think “No harm done, that’ll come out in the process.”
And it does. But those air pockets can be quite large, which means when you can the jars and pull them out of the pressure canner, those bubbles have risen to the top, resulting in a big drop in liquid levels.
“You think ‘My liquid cooked away,’” Robin said. “(But) it didn’t.”
So, to deal with this issue, take that little plastic stick (or a clean spoon, or a butter knife, or a Popsicle stick, or whatever) and pop those suckers. It’s kind of satisfying.
4. Packing the jars too tightly
At the end of every canning process, you’ll have a handful of veggies that just won’t quite fill up a jar. So you think, well, I’ll just cram that in the top of another jar.
Well, that’s problematic.
That extra product takes up space. And while that half inch or so of empty space between the contents of a jar and a lid may not seem like a big deal, that space is crucial. It prevents moisture from degrading the seal of a jar. Pack in too many veggies and that seal can become compromised. That means in the winter time, when you’re looking forward to that nice jar of green beans in the cupboard, you get a gunky sludgy mess instead.
So take those extra green beans — or whatever — and throw them in a cast iron skillet with some olive oil and minced garlic (that you grew yourself) and have a little snack instead. You deserve it. 
5. Reusing lids
With a few exceptions, canning lids are one and done. That means no matter how good a lid looks after using it, don’t use it again.
“A lot of people don’t realize not to do that,” Robin said.
The rubber seals on canning lids develop tears and fissures during the first use. Sometime the tears are microscopic, meaning the seal will look pristine to the naked eye, but still be unable to hold a seal. And sometime, the heat from the canning process can close the tears up which means the jars will seal at first, but as soon as the jar cools enough, it will open up leading to air and bacteria exposure. So don’t reuse your lids!
The biggest tip from Robin is the simplest, however: “If it doesn’t look right, if it doesn’t smell right, don’t eat it.”
Q: Regarding reuse of canning lids, if I thoroughly wash the lid and air dry it, is it ok to use it on a mason jar full of dry goods with a vacuum sealer? I can’t think of a reason this would be harmful since I’m not trying to “can” dried garbanzo beans, just keep them airtight.
A: I do the same thing and was going to post the same comment as you did. I think doing that kind of gets rid of that itch to reuse and not throw away. I use many canning jars for just plain food storage. Things like flour, cornmeal, dehydrated mushrooms, and grits.