Homesteading & Survival · Homesteading & Survival Courses
Free preview
Choose a safe preservation method
Lesson 1 of Home Canning and Food Preservation. Anyone can read this lesson with no account. Every lesson after this one is for students.
Can food with tested processes
Learn why botulism drives every canning rule, and choose freezing, drying, pickling or canning for a food based on its acidity and your equipment.
After this lesson you can explain why green beans need a pressure canner and apples do not, and choose a safe preservation method for any food you are likely to have in quantity.
1The reason behind every canning rule: botulism
Clostridium botulinum is a bacterium that lives in soil and water as a hardy, dormant spore. Spores are on fresh vegetables all the time and do no harm there, because they need three things to wake up, grow and make their toxin:
- no oxygen
- moisture
- low acid (a pH above 4.6)
A sealed jar of green beans, meat or plain vegetables supplies all three. The toxin causes botulism, a paralyzing illness that can kill. CDC lists improperly home-canned, preserved or fermented foods as common sources.
Why a boiling-water canner is not enough. Water boils at 212°F at sea level, and lower at higher elevations. NCHFP explains that botulinum spores are very hard to destroy at boiling-water temperatures. Low-acid foods need 240°F to 250°F, which a pressure canner reaches at 10 to 15 pounds of pressure. Boiling longer does not get the jar hotter, so "an extra hour in the pot" does nothing for safety.
Why acid foods can use boiling water. In foods with a pH of 4.6 or lower (most fruits, properly acidified tomatoes, pickles), spores cannot grow, so boiling-water heat that destroys molds, yeasts and other bacteria is enough.
A sealed lid proves only that a vacuum formed. It says nothing about whether the jar got hot enough for long enough.
2Your options
| Method | Good for | Needs |
|---|---|---|
| Refrigerate | Short-term leftovers | Steady 40°F or below |
| Freeze | Most vegetables, meat, cooked dishes | Steady 0°F and an outage plan |
| Dry | Fruit, herbs, some vegetables, jerky | Food-specific directions, dry storage |
| Pickle or ferment | Cucumbers, cabbage | Exact tested salt and acid ratios |
| Boiling-water can | Fruit, acidified tomatoes, pickles, jams | A tested recipe |
| Pressure can | Vegetables, meat, beans, soups | A pressure canner and a tested recipe |
NCHFP rules out oven canning, open-kettle canning, dishwashers and microwaves. Electric multicookers with a "canning" button are not tested pressure canners for USDA processes.
3Worked example
A neighbor gives you 10 pounds of green beans. You own only a large stockpot.
- Green beans are low-acid. Without a pressure canner, canning is off the table.
- Your freezer has room, so you blanch and freeze most of them following tested directions.
- You cook a big pot for dinner and give a bag to a friend.
- You add "pressure canner, dial gauge checked" to your wish list.
4Practice
- List four foods you are likely to have in quantity this year.
- For each, mark low-acid or acid. Use NCHFP's site if unsure.
- Choose a method from the table that fits your equipment and freezer space.
- Find and bookmark one NCHFP or extension page for each choice.
Expected result: a four-row chart with a method and a source link for every food. If a food has no tested method you can use, write "freeze, eat fresh or share."
5Self-check
1. Why can a sealed jar of green beans still be dangerous?
Show answer
The seal only shows a vacuum. Botulinum spores survive 212°F and can grow in a sealed, low-acid jar.
2. What temperature range kills spores in low-acid food, and how do you reach it?
Show answer
240°F to 250°F, in a pressure canner at 10 to 15 pounds of pressure.
3. Will boiling green beans for three hours make them safe to shelve?
Show answer
No. Boiling water cannot get hotter than 212°F.
6Keep for your binder
Save your four-food chart. Next lesson teaches you to read an NCHFP recipe and find your exact processing time.
- NCHFP: Ensuring Safe Canned Foods, spores, pH 4.6 and 240°F to 250°F.
- NCHFP: Equipment and Methods Not Recommended
- CDC: About Botulism, common sources.
Continue with the full course
This free preview is lesson 1 only. Enroll to open the rest of Home Canning and Food Preservation.