We’re not always sticklers for rules in the kitchen, but when it comes to canning rules, we obey! Keep your foods safe while water-bath canning (aka boiling-water canning) and pressure canning with these rules.
If you’re a competent cook and baker, you’re probably confident making changes or swaps to recipes based on flavor preferences, ingredients on hand, etc. 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 lacking salt or not rising correctly. You could accidentally create food that makes you sick! Not to be overdramatic, but it's true: It’s possible you could can a food improperly, resulting in botulism, which can kill. Not to worry: People have been canning food safely for centuries. If you follow our rules (and a reliable 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 outcome if you choose wrong. 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 in the bottom—is used for high-acid foods (like many fruits), which naturally resist bacteria growth. Pressure canners are used with low-acid foods (like veggies and meats) and recipes that are especially prone to harboring harmful microorganisms. They heat food hotter than boiling-water canners. Recipes will specify which type of canner is appropriate.
2. Choose the Right Jars
Always use jars made specifically for canning. They are designed to hold up under the high pressures of canning. Don't use glass jars 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. And avoid jars with chipped edges or cracks because that can affect the seal or result in a jar that breaks in the canner, which is a nightmare to clean up. Use the jar size specified in the recipe because it could take a different length of time to achieve the critical internal temperature in a larger or smaller jar. Even though vintage canning jars may look cute, don't use them for canning, either, as they can easily crack or chip while processing.
Canning jars come in regular-mouth and wide-mouth varieties. Regular-mouth jars are good for foods like jams, jellies, mustards, and pie fillings. Wide-mouth jars are best for salsas, relishes, fruit butters, pickles, and tomatoes.
3. Don’t Reuse Lids
Use the special two-piece lids manufactured for canning (see an image of the lids in the photo above with the jars). You can reuse the rings, but do not reuse canning lids. The lids have a sticky red compound that seals the jar. After one use, you can’t trust that compound to seal properly again. Improper seal = 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 like these lids 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 canning equipment in hot, soapy water; rinse thoroughly. Sterilize jars. Pack hot foods into hot jars one at a time rather than assembly-line style to be sure jars stay hot. Take only one sterilized jar out of the canner at a time. As soon as it is filled, place it back in the simmering water in the canner. Wipe jar rims after filling to be sure there’s no gunk preventing a proper seal. Have we mentioned how important the seal is?
5. Measure Headspace and Don’t Overfill or Underfill
Canning recipes will always call for a specific headspace to leave when you're filling canning jars. Headspace is the space from the top of the food in the jar to the top of the jar 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 probably left too much headspace.
6. Don’t Overtighten Lids
We get it: You want to be extra safe when canning. But overtightening the bands will have the opposite result. A band screwed on too tightly may not create the vacuum seal you need. Twist bands on just tight enough that you could turn the band another ¼ to ½ inch tighter (aka fingertip tight).