How to pressure-can low-acid vegetables

This page walks a first safe pint of a low-acid vegetable from prep to cool. It is not a substitute for the current directions at the National Center for Home Food Preservation or the USDA Complete Guide to Home Canning. Look up the food you are actually canning before you light the burner. The times and pressures below are from those sources. We did not invent them.

Why a boiling-water bath is the wrong tool

Most plain vegetables sit above pH 4.6. That is the line home canners use. Below it, food is high-acid: most fruits, pickles, jams, and tomatoes that have been acidified the way a tested recipe says. Those can go in a boiling-water bath. Above it, food is low-acid. Green beans, carrots, corn, plain pumpkin, greens, and almost every other garden vegetable belong on that side.

A boiling-water bath tops out around 212°F at sea level — less as you go up in elevation. That is not hot enough to deal with the spores that cause botulism in a low-acid jar. A pressure canner, run at the right pressure for your altitude, gets the jar hotter, around 240°F at the usual home-canning pressures. That is the method USDA and NCHFP publish for these foods.

There is no safe boiling-water-bath option for green beans or other low-acid vegetables. Not if you boil longer. Not if you add extra salt. Not if someone in the family did it that way and nobody got sick. Botulism can be odorless. Under-processed home-canned vegetables have killed people.

A pressure cooker that is not a pressure canner is not a substitute. USDA processes were tested in pressure canners large enough to hold at least four quart jars, with a rack, a vent, and a gauge or weight that can hold a known pressure for a known time. A small cooker, an electric multi-cooker, or a stockpot with the lid clamped shut is not that tool. If that is what you have, do not can low-acid food. Freeze it, dry it, or eat it.

What has to be on the counter

• A pressure canner with a working dial gauge or weighted gauge, a rack, and a clear vent. Read the canner manual for how your weight rocks or jiggles.
• Canning jars with clean, un-nicked rims. New flat lids. Ring bands that screw down without rust flakes.
• A jar lifter, a clean cloth for rims, and a way to measure 1-inch headspace.
• The current NCHFP or USDA directions for the food in front of you — not a memory, not a comment thread.
• Your elevation, in feet. If you do not know it, look it up before you start. Guessing low is how jars get under-processed.

Dial gauges go out of calibration. Have yours checked for accuracy every year before the season starts. County Extension offices do this. If the gauge is more than two pounds off, replace it. If it is less than two pounds off, adjust so the canner actually reaches the required pressure. Weighted gauges do not go out of calibration the same way. They still need a clear vent and the right weight for your altitude.

Salt is optional flavor. It is not a preservative in these vegetable packs. You can leave it out. If you add it, use the amount on the NCHFP page for that food.

You also need a stove that can hold a heavy canner at a steady heat, and enough clean water to fill the jars and the canner.

Step-by-step: prep, fill, vent, process, cool

Work one food at a time. Examples here are snap or wax beans, sliced or diced carrots, and corn. For anything else, open the NCHFP page for that vegetable and follow it.

Prep the food. Wash. Trim. Cut to the size the directions call for. For beans: snap the ends and break into pieces. For carrots: peel, then slice or dice. For whole-kernel corn: husk, silk, and cut kernels at about three-quarters of their depth; do not scrape the cob. Cream-style corn is a different pack — see the table.

Hot pack or raw pack, as the tested directions allow. Headspace is 1 inch for every example on this page.

• Beans, hot pack: Cover with boiling water and boil 5 minutes. Fill jars loosely. Leave 1-inch headspace. Cover with the boiling cooking liquid.
• Beans, raw pack: Pack tightly. Leave 1-inch headspace. Cover with boiling water.
• Carrots and whole-kernel corn: Hot pack is heated in water first, then packed hot; raw pack is packed and covered with boiling water. One-inch headspace either way. Use the NCHFP page for that food so you do not invent a hybrid.

Wipe the rims. Apply new lids. Screw bands fingertip-tight. Do not over-crank. Do not reuse a flat lid that already sealed once.

Load the canner. Rack in. Water 2 to 3 inches deep unless the directions for that food say more. Stand the jars upright on the rack. Lock the lid. Leave the vent open.

Vent. Heat on high until you have a continuous, visible funnel of steam from the open vent. Then time 10 minutes of that steam. USDA requires this. Air left in the canner lowers the temperature you get at a given pressure. A canner that was never vented can read the right pounds and still under-process the food.

Pressurize. After the 10-minute vent, put the weight on, or close the petcock. Wait until the canner is at the required pressure: the dial at the PSI in the table below, or a weighted gauge rocking or jiggling the way the canner manual describes. Start the process time only then. Do not count the heat-up.

Hold a steady pressure at or slightly above the target. If pressure drops below the required amount at any time, bring it back and restart the full process time from the beginning. That is a USDA rule, not a suggestion.

Cool. When the time is up, turn off the heat. Let pressure return to zero naturally. Do not run cold water over the canner. Do not pull the weight to hurry it. Quick-cooling can warp a lid, siphon jars, and leave food under-processed. For a weighted-gauge canner, wait until it is fully depressurized — often 30 to 45 minutes, longer with a heavy load. Then remove the weight, wait about 10 more minutes, and open the lid away from your face.

Lift jars straight up. Set them on a towel with space between them. Leave them alone 12 to 24 hours. Do not retighten bands. Do not press the center of a lid until the jars are fully cool.

Altitude is not optional

Process times in the table stay the same. The pressure changes with elevation. Using a sea-level pressure at 4,000 feet is how you get a jar that looks sealed and is not safe.

Dial-gauge pressure for green beans, carrots, and whole-kernel corn (same PSI table):

Weighted-gauge pressure:

Source: USDA Complete Guide to Home Canning / National Center for Home Food Preservation.

Process times (hot or raw pack unless noted). Headspace is 1 inch for every row. Times are USDA / NCHFP.

Look up any other vegetable on nchfp.uga.edu before you can it. A quart is not a doubled pint. Do not shorten a time because the beans look done.

Read the seal; handle a failed jar

When the jars are fully cool, take the bands off. Press the center of each lid. A sealed lid is concave and does not flex. A lid that pops, flexes, or comes off in your hand did not seal.

Failed seal the day you can: Refrigerate that jar and eat it soon, or reprocess only if you are still inside the rules for that food — new lid, full process time, food still in the condition the directions assume. If you are not sure you are still inside those rules, do not put it on the shelf.

Later, on the shelf: Bulging lid. Spurting liquid when opened. Mold. An off smell. A jar that unseals in storage. Cloudiness that was not there. Any of that, and the jar is not food.

Never taste a suspect jar. When in doubt, throw it out. Botulism toxin can be odorless and invisible. A sealed lid is not a promise the food was processed long enough or hot enough. Store sealed jars cool, dark, and dry, and look at them again before you open one.

Wash the jars, label the food and the date, and put them into the same rotation as the rest of a 90-day pantry.

What this method is for — and not

For: Plain, tested packs of low-acid vegetables — beans from a first-year garden, carrots, corn — in a real pressure canner, at the pressure for your altitude, for the published time.

Not for:

• A boiling-water bath of green beans, or any other “just boil it longer” shortcut.
• A pressure cooker that is not a pressure canner.
• Mixtures you invented. “A little of everything” from the crisper is not a tested process. If you want mixed vegetables, use the NCHFP mixed-vegetable directions, not a freehand combo.
• Dry-canning raw vegetables — jars of dry beans or dry carrots with no liquid. That is an unsafe practice. NCHFP says so in those words.
• Dairy. Do not can milk, butter, or cream.
• Meat, fish, or a meal-in-a-jar as your first project. Those have their own tested pages. Learn this vegetable process first.
• Thickeners, flour, rice, pasta, or extra fat added to a vegetable jar unless a tested recipe calls for them.

If you do not have a pressure canner, or you are not willing to vent, time, and cool the way this page describes, do not can low-acid vegetables. Dry the surplus or eat it. A method that can kill someone does not get a workaround on this page.

Next: How to dehydrate food without a fancy setup — when drying is the better first move.