I brought my dial gauge to extension last April and it was off by two pounds. I had been underprocessing beans without knowing. Get the gauge checked.
Pressure canning versus water bath: when each is safe
MEMara Ellison
Aug 13, 2026 · Shoreham, VT
Notes here are members’ methods, not professional advice. Canning, water treatment, and first aid can be dangerous if done wrong. Read the safety disclaimer.
Puts up 400 jars a year from a half-acre in the Champlain Valley. Teaches water-bath and pressure canning without the folklore.
I get this question every workshop, usually from someone holding a beautiful pot of green beans and a water-bath canner they inherited. I would like them to keep their family. So we talk about acid.
The line
Foods at pH 4.6 or below can be water-bathed because botulism cannot grow there. That is most pickles, most jams, most fruit, and tomatoes with added acid. Low-acid foods — vegetables, meat, beans, soup — need a pressure canner that reaches 240°F. A boiling-water bath never gets there.
Tomatoes are the gray area
Modern tomatoes are often milder than the ones in old books. I add two tablespoons of bottled lemon juice per quart, or a half teaspoon of citric acid, every time. Then I water-bath. If I mix tomatoes with low-acid vegetables I pressure can the whole thing.
What a pressure canner is not
It is not a pressure cooker with a dream. Use a canner with a calibrated gauge or a weighted regulator, a rack, and a manual from this decade. Have the gauge checked at the extension office once a year. A gauge that reads low is how people underprocess.
Altitude
Water boils cooler as you go up. Add time for water bath, add pressure for a dial-gauge canner. The USDA tables exist so you do not have to invent this. I keep a printed copy in the drawer with the jar lifter.
If a recipe from a blog disagrees with the USDA or your extension service, the blog is wrong. I say this as someone who writes on the internet.