6 Rules for Canning You Should Never, Ever Break

We're not always sticklers for rules, but when it comes to the ones for canning, we adhere faithfully.

If you're a competent cook and baker, you're probably confident making changes or swaps to recipes. By all means, keep it up. But when it comes to canning recipes, a change to the recipe, or a mistake in the process, could result in much worse than a dish needing salt or not rising correctly. You could accidentally be creating food that will make you sick. Not to be overdramatic, but it's true: Canning a food improperly can result in botulism, which can be life-threatening. But don't worry, canning food safely is a centuries-old skill. If you follow these rules (and a reliably tested recipe), you'll be just fine.

1. Use the Right Canner

This is the big one, the one that could have the most catastrophic result if you make the wrong choice. There are two types of canners—boiling-water canners and pressure canners. The boiling-water canner—basically a big pot with a lid and a rack for holding jars—is used for high-acid foods (like many fruits), which naturally resist bacteria growth. Pressure canners are used for low-acid foods (like vegetables and meats) and recipes that are especially prone to harboring harmful microorganisms. Pressure canners reach a higher heat than boiling-water canners. Recipes will often specify which type of canner is appropriate.

2. Choose the Right Jars

canning equiptment
Jason Donnelly

Always use jars made specifically for canning. They're designed to hold up under the high pressures of canning. Don't use glass jars left over from purchased food, even if they look like canning jars. Don't use jars that look different from the canning jars currently on the market. Avoid jars with chipped edges or cracks, because that can affect the seal, or result in breaking in the canner, which is a nightmare to clean up. Use the exact jar size specified in the recipe, because a larger or smaller jar could take a different length of time to achieve the critical internal temperature. Even though vintage canning jars may look cute, don't use them for canning, either, as they can easily crack or chip during processing.

Canning jars come in regular-mouth ($11, Walmart) and wide-mouth ($14, Walmart) varieties. Regular-mouth jars are good for jams, jellies, mustards, and pie fillings. Wide-mouth jars are best for salsas, relishes, fruit butters, pickles, and tomatoes.

3. Don’t Reuse Lids

If you're new to canning, you might be wondering if the lids can be reused. Sorry, but it's a no-go. The special two-piece lids ($4, Walmart) are manufactured for canning (see an image of the lids in the photo of jars above). You can reuse the rings, but do not reuse the lids. They have a sticky red compound that seals the jar. After one use, you can't trust the compound to seal properly a second time, and an improper seal equals unsafe food. When you buy new jars, both lids and bands will be included, but you can also purchase new lids separately. Always buy canning supplies from a trusted source, and check for flaws before using.

4. Keep Everything Clean (Really Clean) and Hot

Keep everything scrupulously clean. Thoroughly wash your canning jars, lids, funnel, and other equipment in hot, soapy water, then rinse thoroughly. Sterilize the jars. To be sure the jars remain safely hot, remove only one sterilized jar at a time from the canner and pack hot foods into the hot jar, always one at a time, rather than assembly-line style. As soon as the jar is filled, place it back in the simmering water. Wipe the jars' rims after filling so there's no gunk preventing a proper seal. Have we mentioned how important the seal is?

ruler jar canning relish
Karla Conrad

5. Be Mindful of Canning Headspace

Canning recipes will always call for a specific headspace to leave when you're filling jars. Headspace is the space from the top of the food in the jar to the top of the rim. An overfilled or underfilled jar may not seal correctly, which, as you now know, results in unsafe food. It's all about the seal. If you're losing liquid during processing or find mold during storage, you've probably left too much headspace.

twist canning lid jar fingertip tight
Karla Conrad

6. Don’t Overtighten Lids

We get it: You want to be extra-safe when canning. But over-tightening the bands will have the opposite result. A band screwed on too tightly may not create the vacuum seal you need. Twist the bands on just tightly enough that you could turn it another ¼- to ½-inch tighter (fingertip tight).

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