Pressure Canning (Low-Acid Foods — Refer Out)

Why this page refers out

Low-acid foods — most vegetables, meats, poultry, seafood, beans, and plain (un-acidified) tomatoes — sit above pH 4.6. At that acidity, Clostridium botulinum spores can survive a boiling-water bath and then germinate inside the anaerobic, sealed jar, producing a toxin that is odorless, tasteless, and potentially fatal. The only home method validated to make these foods safe is pressure canning, and it carries enough margin for error that we will not abbreviate it here. This page explains the physics and points you to the authoritative, tested schedules — we deliberately do not publish processing times or pressures.

Caution

NEVER water-bath can or steam-can a low-acid food (pH above 4.6). It can grow botulinum toxin even when the jar looks, smells, and tastes normal. Taste is never a safety test — pH is. If a food is above pH 4.6 and you are not pressure canning it from a current tested schedule, do not can it: refrigerate, freeze, or acidify it to bring it under 4.6 first. This site does not publish pressure-canning times or pressures by design — follow the USDA / NCHFP sources below.

The physics: why boiling water is not enough

Water at sea level boils at 100°C / 212°F and will not get hotter no matter how long it boils — added heat just turns more water to steam. Botulinum spores are remarkably heat-resistant and are not reliably destroyed at 212°F. A pressure canner is a sealed vessel: trapping steam raises the internal pressure, and raising the pressure raises the boiling point, so the canner reaches 116–121°C / 240–250°F. That higher temperature, held for a tested time, is what destroys the spores. Boiling-water and steam canners physically cannot reach it, which is why they are unsafe for low-acid foods.

Food acidity	Hazard at 212°F	Required method
pH at or below 4.6 (high-acid / acidified)	Spores cannot germinate	Water-bath canning
pH above 4.6 (low-acid)	Botulinum spores survive and can grow	Pressure canning (per USDA / NCHFP)

Note

Required pressure-canner temperature depends on your altitude and the canner type (dial-gauge vs. weighted-gauge), and the processing time depends on the specific food, pack style, and jar size. These variables are exactly why a generic number is dangerous and a tested, food-specific schedule is mandatory.

Why we don’t publish a schedule

Pressure-canning times and pressures are validated food-by-food, jar-by-jar, and altitude-by-altitude through laboratory heat-penetration and inoculation studies. A wrong number, a wrong jar size, or an uncorrected altitude can leave a jar under-processed and unsafe with no warning sign you can see, smell, or taste. Reproducing or paraphrasing those tables risks introducing exactly the kind of error that causes botulism, so we refer you to the primary sources that maintain and test them.

Where to get tested schedules

🛡️ USDA Complete Guide to Home Canning

The authoritative U.S. reference for low-acid pressure-canning schedules by food and altitude.

⚗️ NCHFP

National Center for Home Food Preservation — current tested processes and step-by-step canner guidance.

• USDA Complete Guide to Home Canning: nchfp.uga.edu — USDA guide & general canning
• NCHFP pressure-canning principles and food-specific schedules: nchfp.uga.edu
• Your local Cooperative Extension office can also test your dial gauge and confirm altitude corrections.

See also

• Acidity and pH and pH safety calculator — find which side of 4.6 your food is on
• Safety and botulism — the hazard this method exists to prevent
• Acidification — an alternative path: bring a borderline food under 4.6 and water-bath it instead
• Water-bath canning — the correct method for high-acid foods
• Preservation hurdles — how acidity, heat, and oxygen combine