Learn the Basics of Pressure Canning to Preserve Food

Don’t be bewildered by the process of pressure canning any longer. We unveil a method that lets you move past your fears and put up home-preserved food.

by Leslie J. WyattOctober 15, 2018
PHOTO: iStock/Thinkstock

There’s perhaps nothing more satisfying than growing your own food, canning it and being able to eat off the supply all winter long. Home-canned summer peaches offer a delicious treat that can top cakes or be eaten alone. Homemade sauces made with a family recipe offer a taste of home and prevent you from having to run out to the grocery store at mealtime. Green beans, corn, okra and more—all of which stemmed from your soil and were put up by your own hands—are there for you to savor year-round. You can do all this through pressure canning.

But for first-time canners, the process can be a bit intimidating. Even I, who grew up in the canning kitchen, was fearful in my first solo attempt at preserving the harvest—tales of exploding pressure canners painting terrifying, vivid pictures in my head.

Pressure canning doesn’t have to be a scary process, though, and I’ve survived more than three decades without more than a hiccup along the way. On the other hand, to avoid disasters that have been passed down through generations, you must follow strict safety protocols. The National Center For Home Food Preservation and your local cooperative extension office are two excellent resources you should consult before you begin canning for the first time. Below is my own personal canning strategy that I hope will help demystify the process, as well.

Pressure Canner Anatomy

A pressure canner consists of basic parts:

  • the body
  • the lid with a dial gauge or weighted gauge plus a safety plug (Lids with dial gages also have a steam vent with a weight, but that weight is only to hold the steam in and does not jiggle like a weighted gauge/petcock.)
  • a gasket, which should be checked every year and replaced if cracked or over-stretched (Mine has lasted nearly 30 years.)
  • a jar rack or flat metal spacer to keep the jars from directly contacting the bottom of the canner
pressure canning
Bug G. Membracid/Flickr

Step 1

Pristine treatment of jars and food help prevent bacteria contamination, raising the percentage of pressure canning success. Wash the jars in hot soapy water, rinse with very hot water, and drain. As an alternative, you can use the hottest cycle in your dishwasher, as long as it doesn’t leave little particles of food residue behind. You can also immerse the jars in water and bring it to a boil to sterilize them, but recognize that the moment air or food touches them, they are technically no longer sterile. Basically, that’s why we’re pressure canning—to kill any remaining bacteria. That said, if you do boil them to check for weakness, you’ve sterilized them for the moment, as well. My preference is to wash them. Be sure to use clean water and a clean brush or cloth reserved just for this purpose. Your normal dish brush or cloth may be harboring bacteria and defeating your purpose.

Step 2

Wash, rinse, drain your canner body, and set it on the largest burner on your stove. The NCHFP advises you to center the canner over a level burner and range. The pressure canner can also be damaged by excess heat, so consult your pressure canner’s manual for information on appropriate burners.

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The general rule of thumb is to add 1 quart clean water to the bottom of your canner. Because some foods require long processing times—90 minutes or more—more water may be required (NCFP mentions 2 to 3 inches). This water will boil to make the steam and cause the pressure to form in the canner once the lid is on and secured.

Start with fresh water each time you load the canner. Jars will come through with less mineral deposits, plus it’s easy to forget to add additional water to compensate for what evaporated during processing. Also, remember that plunging cool jars into very hot water can cause them to crack.

Step 3

Check the lid. This is where my mom used to start to scare me: She’d hold up the lid and peer through the steam vent—that little rocket-shaped metal piece with the hole through it—like a submarine captain looking through her periscope. She’d do this to make sure nothing was clogging it—that’s a good thing. I prefer to blow through it. The point is, check it. If it’s plugged, clear it out. Meanwhile, refuse to tell yourself or your children scary pressure-canner stories.

Step 4

Next comes filling your clean jars. Wash and prepare food as recommended in your canning book or on the USDA website. (Keep in mind that older canning recipes may have outdated safety information, so use a modern and tested recipe.) Pack your food into your jars according to the specs in the canning book/manual, which will vary from food to food.

The thing to remember here is that hot items expand. That means that the contents of the jar need some room to expand. The term for that in the canning world is “head space”—the 1/2- to 1-inch space above the food and below the rim of the jar. Your canning book will tell you how much headspace to leave. Do it their way; otherwise, particles may rise to the height of the jar lid and get under the rubber seal as everything expands with the heat. Particles between the jar rim and lid will prevent sealing.

Step 5

Add salt as indicated in a tested recipe.

Step 6

With a clean cloth or paper towel, wipe the rim of the jar to remove any bits of food or salt that might have gotten on it (see step 4 for rationale). Place the flat piece of the lid on the rim of the jar, following it with the screw-on ring. Tighten the ring snugly: As the metal expands, the ring needs to be tight enough to produce pressure on the rubber seal so it will seal well. However, remember, this is not a strength test—someone has to get the ring off eventually.

Step 7

Load your canner according to your manual.

Step 8

Check your gasket to make sure it is seating well.

Step 9

Secure the canner lid per the directions in your manual. All modern pressure canners have a built-in safety latch in the lid that engages as pressure begins to build. Do not place petcock/weight on the steam vent at this time.

Step 10

Turn the heat on. I start it at just under high heat. It will take a while for the water in the bottom to heat the food in the jars to the point where steam begins to build up (less time if you used the hot-pack method). Depending on your canner, you’ll hear various hissings and bubblings and maybe a few rattlings as jars, water and kettle heat up. This is normal.

As steam begins to build, you’ll hear/see it start to escape through the steam vent and possibly around the rim of the canner until the auto-lock clicks into place. The NCHFP recommends allowing steam to escape for 10 minutes to ensure that air isn’t trapped in the canner. Trapped air can cause lower than recommended temperatures and could result in food spoilage.

Step 11

Place the weight on the steam vent. If your canner has a weighted gauge instead of a dial, place at indicated poundage for the food you’re pressure canning. For example, green beans are listed in my Ball Canning Book as needing 10 pounds of pressure for 20 minutes. For canners with this type of gauge, you’ll know you’re up to temperature when the petcock starts to jiggle. This can seem loud and somewhat unsettling, but it’s exactly what is supposed to be happening.

The weighted gauge/petcock should jiggle several times per minute. Turn the heat down a tad if it jiggles continuously at any point. Conversely, if it goes more than 30 seconds without jiggling, raise the heat slightly.

For a dial gauge, watch the needle until the steam builds to the proper pressure as indicated in your manual. (The gauge should be checked for calibration every year to make sure it is still accurate. Your friendly extension office is the place to go for that.) From this point, keep your eye on that gauge so that the temperature remains constant. This will involve turning down the heat bit by bit as needed, just like with the weighted gauge, stopping when it holds steady at the required temperature.

Step 12

Start your timer only after the petcock jiggles/dial gauge reaches target temp. As noted earlier, you might need to turn the heat down bit by bit over the course of the processing time, so don’t leave it and go off and weed the garden. That would come under one of those behaviors my mom implicated in alleged pressure canner explosions. To avoid all complications, do not leave a pressure canner unattended. Listen for it if you have the weighted gauge type, or check about every 3 to 5 minutes if you have a dial gauge, adjusting the burner temperature as needed.

Step 13

When the timer goes off, turn off the heat and do not touch the canner, lid, petcock or weight. I repeat: Touch nothing! The pressure must dissipate naturally. If you get impatient and jiggle the petcock to get it to release faster or turn a fan on the canner, not only do you shorten the time the heat has to kill bacteria, you risk causing the jars to break under the sudden change of pressure. In this interim time, I ready my next load of jars and/or make myself a cup of coffee.

Step 14

When the safety latch in the canner lid has disengaged, allowing you to remove the lid, you’re ready to remove the jars. Caution: Everything will be scalding hot! Use a special jar lifter (available wherever pressure canning supplies are sold), lift them out, and set them on a heat-safe surface. It’s important that no cold drafts hit the jars in this process. A sudden change in temperature could cause the jar’s surface to contract and break. By the way, have you noticed that jars, rather than canners, seem most likely to explode?

Step 15

As the jars cool, you’ll hear comforting “pops” as the lids seal. Once at room temperature, check each to make sure they’ve sealed. Any jars that don’t seal should be put in the refrigerator and the contents eaten within a week or frozen for later consumption.

Step 16

Unscrew the jar rings, and wash them. (Watch out—sometimes you can cut yourself on the edge of a flat lid.)

Step 17

Dry the lid and jar, mark the date on the top of the lid with a permanent marker, and voila! You did it! Your canning season is off to a great start.