Home Canning: Water-Bath and Pressure Canning

By GoldBlock WorkshopPublished Oct 10, 2026Updated Oct 19, 2026

The short answer

Home canning carries a specific risk: improperly canned low-acid food can contain botulinum toxin; the CDC calls botulism “a medical emergency,” and Ohio State University Extension states that “Botulinum toxin cannot be seen, smelled, or tasted.” The National Center for Home Food Preservation’s rule is to use only research-tested recipes and processing times, followed exactly. Acid foods (pH 4.6 or lower, such as most fruits, pickles and acidified tomatoes) can be processed in a boiling-water canner. Low-acid foods (vegetables, meat, poultry, seafood, beans and soups) must be processed in a pressure canner, because botulinum spores are very hard to destroy at boiling-water temperatures. Adjust for your elevation, test your seals, and never taste food from a jar that looks or smells wrong.

Key numbers

pH 4.6the line between acid foods (boiling-water canner) and low-acid foods (pressure canner)Source: National Center for Home Food Preservation
240 to 250°Ftemperature needed to process low-acid foods, reachable only in a pressure cannerSource: National Center for Home Food Preservation
Above 1,000 ftadd processing time (boiling water) or adjust pressure for your elevationSource: National Center for Home Food Preservation
Every yearcheck dial pressure gauges for accuracy before useSource: National Center for Home Food Preservation

About this page

This page is education: it explains how a subject works so you can understand it, hire the right professional, or train to become one. It is not professional advice, and we hold no professional licenses. For decisions about your own health, home, money or safety, talk to a qualified professional. Official sources cited are U.S. agencies; rules differ in other countries.

It explains how canning works and why low-acid foods must be pressure canned; it deliberately does not reprint recipes or processing times. For every product, follow the tested procedure at the links on this page, and learn hands-on from an experienced canner, a Master Food Preserver or your local extension office before canning low-acid foods. Statements were checked against the National Center for Home Food Preservation, the CDC and the UC Master Food Preserver program, as cited.

How this page was made: researched and drafted with AI assistance, checked against the sources listed at the bottom, checked again by a separate AI reviewer that did not write it, and reviewed by GoldBlock Workshop before publication. We can still miss things; if you find an error, tell us. This page has no affiliate links. We received no free products for it. How we research and review. What our content is and is not.

How canning keeps food safe

Canning heats food in sealed jars long enough to destroy the microorganisms that cause spoilage and illness, then forms a vacuum seal that keeps new ones out. The danger is Clostridium botulinum: its spores survive boiling-water temperatures and can grow and make toxin in a sealed, low-acid, low-oxygen jar. That is why the method depends on the food’s acidity:

Acid foods have a pH of 4.6 or lower. Their acidity blocks the bacteria or lets heat destroy them faster, so they can be processed in a boiling-water canner. NCHFP gives processing times from 5 to 85 minutes depending on the food.
Low-acid foods have a pH above 4.6. They must reach 240 to 250°F, which only a pressure canner at 10 to 15 pounds of pressure can do.

Some tomatoes are slightly above pH 4.6, so tested recipes add lemon juice or citric acid (NCHFP). Mixtures such as salsa, soups and stews follow their own tested procedures; adding low-acid vegetables changes the whole jar.

Tested recipes only

NCHFP’s key controls are the right canning method and “the recommended research-based process times found in the USDA’s Complete Guide to Home Canning.” In practice that means:

Use a current tested process from USDA, NCHFP or a university extension service, made for your equipment and your food, and follow your canner manufacturer’s operating instructions.
Follow ingredient amounts, jar sizes, headspace, packing method and processing time exactly.
For pickles, NCHFP says: “Do not alter vinegar, food, or water proportions in a recipe or use a vinegar with unknown acidity.”

Adjust for your elevation

Water boils at lower temperatures as elevation rises. NCHFP warns that food “may spoil if you fail to add process time for lower boiling-water temperatures at elevations above 1,000 feet,” and that pressure canning must use “the correct time and pressure specified for your elevation.” NCHFP explains how to find your elevation.

Equipment and pressure canner basics

Use mason-type canning jars with new lids, a pressure canner made for home canning (not a pressure cooker), and a dial gauge checked for accuracy each year (NCHFP).

Jars and lids: use mason-type canning jars with new two-piece self-sealing lids, as the tested recipe specifies. NCHFP does not recommend jars with wire bails or zinc caps for canning.
Pressure canners (not pressure cookers): NCHFP says pressure saucepans with smaller capacities “are not recommended for use in canning.” Use a canner made for home canning.
Check dial gauges for accuracy before use each year. Many county Cooperative Extension offices test them, or ask the canner’s manufacturer (NCHFP).
Vent the canner for 10 minutes with steam flowing freely before pressurizing, and do not force-cool it: let the pressure drop on its own.

Cooling, seals and storage

Let jars cool undisturbed, then test the seals: NCHFP: “The lid should be concave (curved down slightly in the center).” If a jar did not seal, NCHFP gives three options: reprocess it within 24 hours using the same processing time (check the jar rim for nicks and use a new, properly prepared lid), freeze it (NCHFP’s containers for freezing page: “leave extra headspace to allow for expansion of foods during freezing,” or the jar can break at the neck), or refrigerate it and eat it within several days. Reprocessing lowers quality, and none of these options rescues food that was not canned with a tested process in the first place.

For storage, NCHFP advises:

Remove ring bands, wash and dry them, and store jars without them to keep them dry.
“For best quality, store between 50 and 70°F.”
“Do not store jars above 95°F or near hot pipes, a range, a furnace, in an uninsulated attic, or in direct sunlight.” Damp areas can corrode lids and break seals.
“Can no more food than you will use within a year unless directions for a specific food provide other advice.”

Spotting and disposing of spoiled jars

Before opening, look for swollen or unsealed lids, spurting liquid, rising bubbles, unnatural color, cotton-like mold, and unnatural odors when opened.

⚠ If a jar is suspect

NCHFP: “Do not taste food from a jar with an unsealed lid or food that shows signs of spoilage.” NCHFP’s procedure treats any suspect low-acid jar, tomatoes included, as possibly containing botulinum toxin. Put sealed suspect jars in a heavy garbage bag in the trash. Unsealed, open or leaking jars must be detoxified before disposal by boiling them in a covered pot with at least 1 inch of water above the jars for 30 minutes. Wear disposable rubber or heavy plastic gloves throughout. NCHFP’s cleanup uses a fresh solution of 1 part unscented liquid household chlorine bleach (5 to 6% sodium hypochlorite) to 5 parts clean water: wet contaminated surfaces and let it stand 30 minutes, wipe up with paper towels and bag them, apply the solution again for another 30 minutes, rinse, then wash everything that was exposed, including clothing. Follow the full NCHFP procedure: Identifying and Handling Spoiled Canned Food. CDC: “Botulism is a medical emergency,” and “People with symptoms should see a doctor or go to the emergency room immediately.” Its common symptoms: “Difficulty swallowing,” “Muscle weakness,” “Double vision,” “Drooping eyelids,” “Blurry vision,” “Slurred speech,” “Difficulty breathing,” “Difficulty moving the eyes.”

Common questions

Can I water-bath can vegetables or meat?

NCHFP classes vegetables, meat, poultry, seafood, beans and soups as low-acid foods, which must reach 240 to 250°F in a pressure canner; vegetables in a tested pickling recipe follow the boiling-water process that recipe gives, because the recipe’s acid changes the food’s pH. Boiling-water temperatures do not destroy botulinum spores (NCHFP).

Can I use my Instant Pot or electric pressure cooker for canning?

NCHFP: “our canning processes are not recommended for use in electric pressure multi-cookers at this time.” Its tested processes are written for stovetop pressure canners (low-acid foods) and boiling-water canners (acid foods).

How long do home-canned foods last?

NCHFP advises canning no more than you will use within a year and storing jars between 50 and 70°F for best quality, never above 95°F.

Do I need to adjust canning for altitude?

NCHFP: food “may spoil if you fail to add process time for lower boiling-water temperatures at elevations above 1,000 feet,” and pressure canning uses “the correct time and pressure specified for your elevation.” Each NCHFP process gives the adjustments.

Is there a test strip or home test for botulism?

No. CDC explains that botulinum toxin is confirmed by laboratory testing done “through your state public health department laboratory,” and “this specialized testing often takes days to complete.” UC Master Food Preservers of San Joaquin County (UC ANR, September 18, 2023): “Home pH testing methods often lack the precision and reliability required for safe home canning,” and “pH meters and strips used in homes may not provide accurate readings, which can lead to unreliable results.” The controls NCHFP names are the tested process, the seal, and not tasting food from a suspect jar.

Can old family canning recipes be used?

NCHFP’s rule applies: a recipe is used only if it matches a current research-tested procedure. NCHFP says open-kettle canning and processing freshly filled jars in conventional ovens, microwave ovens and dishwashers are not recommended “because these practices do not prevent all risks of spoilage,” so an older recipe that relies on them is not a tested procedure.

Where to go next

Food PreservationChoosing between freezing, drying, pickling, fermenting, canning and curing.
Long-Term Food StorageStoring dry staples for years.
Home Food GardenGrowing the harvest you will preserve.
Food PreparednessThe whole food system, layer by layer.

Sources

All from the National Center for Home Food Preservation (University of Georgia, with USDA support); each page fetched live by an independent reviewer on October 18, 2026 (history entry 67) and not refetched in the October 19, 2026 audit:

Ensuring Safe Canned Foods. pH 4.6; 240 to 250°F; botulinum spores and boiling water; boiling-water times; tested process times.
Equipment and Methods Not Recommended, Canning in Electric Multi-Cookers and Using Atmospheric Steam Canners.
How to Use Boiling Water and Pressure Canners. Dial gauges, venting, natural cooling, pressure saucepans.
NCHFP: Cooling Jars and Testing Jar Seals. Unsealed jars: reprocess within 24 hours, freeze, or refrigerate and use within several days.
Selecting the Correct Processing Time and Find Your Elevation.
Storing Home Canned Foods.
Identifying and Handling Spoiled Canned Food.
General Information on Pickling.
USDA Complete Guide to Home Canning (2015 revision).

Also (all read October 19, 2026): CDC: Symptoms of Botulism (last reviewed April 1, 2024; “Botulism is a medical emergency”; symptom list); CDC: Clinical Overview of Botulism (last reviewed April 22, 2024; testing “through your state public health department laboratory”; “often takes days to complete”); Ohio State University Extension: Botulism: What You Don’t See or Smell Can Still Hurt You, HYG-5567 (Candace J. Heer and Nicole Arnold, March 10, 2025; “Botulinum toxin cannot be seen, smelled, or tasted”); UC Master Food Preservers of San Joaquin County: Preservation Notes (UC ANR, September 18, 2023; home pH testing).