Water-bath and pressure canning

Clostridium botulinum spores are on most fresh food. Sealed in a jar of moist, low-acid food at 40–120°F with almost no oxygen, surviving spores can make a deadly toxin within 3–4 days. A few nanograms of toxin can make someone ill.

Which foods go where

USDA: "Pressure canning is the only recommended method for canning meat, poultry, seafood, and vegetables".

Why this matters: home-canned vegetables are the most common cause of botulism outbreaks in the US.

• Ohio, 2015: 25 confirmed cases and 1 death, from potatoes canned in a boiling-water canner.

• New York City, 2018: peas canned with a peach-preserves boiling-water recipe.

Tomatoes: add acid to every jar

Put the acid straight into each jar before filling. Sugar can offset the sour taste.

• Why every tomato needs it:

  • Some varieties are at or above pH 4.6; 15 of 105 tested in Illinois were.
  • Overripe or damaged fruit loses acid.
  • Don't can tomatoes from dead or frost-killed vines.

• Acid is needed even when pressure canning tomatoes; those times assume it was added.

• Bottled lemon juice, never fresh, and store-bought 5% vinegar, never homemade, because their acidity varies.

• Wisconsin advises against vinegar in plain tomatoes, while USDA allows it. Lemon juice or citric acid avoids the question.

Figs

Figs are slightly above pH 4.6. Add the same amounts as for tomatoes: 2 Tbsp bottled lemon juice or ½ tsp citric acid per quart.

Pickles

• Use 5% acidity (50-grain) white or cider vinegar. Never dilute it or change the vinegar, food or water amounts.

• 4% vinegar used by mistake:

  • canned less than 24 hours ago: refrigerate the jars
  • canned longer ago: discard them

• Fermented pickles and sauerkraut cure about 3 weeks; don't cut the salt. Quick (fresh-pack) pickles get their acid from vinegar.

Salsa

Salsa mixes acid tomatoes with low-acid peppers and onions, so the recipe's balance is what makes it safe.

The only safe changes:

• Swap bottled lemon juice for vinegar. Never swap vinegar for lemon juice.

• Change the dried spices.

Don't:

• Add more peppers or onions, or use bigger peppers.

• Thicken with flour or cornstarch.

• Can a salsa recipe you made up. Freeze or refrigerate it instead.

Jams and jellies

• Sugar helps preserve them. Too little prevents gelling and lets mold grow. For low-sugar spreads, use pectin made for it and follow the package.

• No paraffin wax seals; process in a boiling-water canner.

• Mold on jam means the whole jar goes, not just the top.

Water boils at lower temperatures as you go up: 212°F at sea level, 208°F at 2,000 ft, 204°F at 4,000, 201°F at 6,000, 197°F at 8,000. So canning at altitude needs more time or more pressure.

Boiling-water canner

Use the time listed for your elevation in the tested recipe. For example, USDA's hot-packed peaches in pints:

Generic extension tables (+5/+10/+15/+20 min) don't always match the recipe tables, so the recipe wins.

Pressure canner

re-checked in the USDA PDF. The table is for USDA recipes listed at 11 lb (dial) and 10 lb (weighted). Above 8,000 ft, USDA has no table; extension services use 15 lb.

Find your elevation: use the USGS National Map, or call your county extension office. Examples:

• Salt Lake City about 4,265 ft

• Albuquerque about 5,000 ft; Santa Fe about 7,000 ft

For acid foods only, with a tested recipe. Sources:.

1. 1

   Get ready. Wash jars and keep them hot until filling. Sterilize jars only if the process time is under 10 minutes: boil 10 minutes, plus 1 minute per 1,000 ft above 1,000 ft.

2. 2

   Heat the canner: rack in, about half full of water. Use about 140°F for raw-packed food and 180°F for hot-packed food.

3. 3

   Fill the jars following the recipe and leave the right headspace (the gap at the top): ¼ in for jams and jellies, ½ in for fruits and tomatoes (pickles: follow the recipe).

4. 4

   Clean up the jars. Run a plastic spatula around the inside to release bubbles, and wipe the rims clean.

5. 5

   Put on lids and bands, fingertip-tight.

6. 6

   Load the jars upright with a jar lifter. Water should be at least 1 in over the jar tops, or 2 in for processes over 30 minutes.

7. 7

   Cover and bring to a full rolling boil, then start timing. Use the recipe's time for your elevation.

8. 8

   Keep it boiling the whole time. If the boil stops, bring it back and restart the time from zero.

9. 9

   When time is up, turn off the heat, take off the lid, and wait 5 minutes.

10. 10

    Lift jars straight up and set them on a towel, 1 in apart, out of drafts. Leave them alone 12–24 hours. Don't tighten the bands.

Required for all low-acid foods. Sources:.

1. 1

   Check the canner: the gasket is in good shape, the vent pipe is clear, and the dial gauge was tested this year.

2. 2

   Add 2–3 in of hot water (or what the recipe says) and set the rack in.

3. 3

   Fill the jars following the recipe, leaving 1–1¼ in headspace. Remove bubbles, wipe rims, and put on lids and bands.

4. 4

   Load the jars and lock the lid, with the weight off or the petcock open.

5. 5

   Heat on high until steam pours out steadily, then vent for 10 minutes.

6. 6

   Close the vent (put the weight on or close the petcock). Pressure builds over the next few minutes.

7. 7

   Start timing when the gauge reaches the right pressure for your elevation, or when the weight jiggles or rocks as the maker describes.

8. 8

   Hold steady pressure, at or just above the target. If it drops below, bring it back up and restart the full time. Big swings force liquid out of the jars.

9. 9

   When time is up, turn off the heat and let it cool on its own. Don't run water over it or open the vent early: "Forced cooling may result in unsafe food or food spoilage".

10. 10

    Open it once pressure reads zero:

    • Remove the weight and wait 10 minutes.
    • Lift the lid tilted away from your face.
11. 11

    Cool the jars 12–24 hours as in “Boiling-water canning, step by step”.

Check seals after 12–24 hours. The lid should curve down and not flex when pressed. Then:

• remove the bands

• wash the jars

• label them with contents and date

Jars that didn't seal:

• Refrigerate and eat within several days, or freeze.

• Or reprocess within 24 hours: empty and reheat the food, use a clean jar and a new lid, and run the tested recipe's full time.

• If the batch didn't follow a tested recipe, throw all of it out, sealed or not.

Store:

• Where: cool, dark and dry, ideally 50–70°F.

• Never above 95°F, by a stove or furnace, in an uninsulated attic or in sunlight.

• Damp spots rust lids.

• How much: only what you'll use in about a year.

Avoid stacking jars. Never go more than 2 layers high, with support between them.

Signs a jar has gone bad

• a bulging or swollen lid, or one that isn't curved down

• leaking, or streaks of dried food from the top

• rising bubbles

• liquid that spurts or foams when opened

• odd color, a bad smell, or mold

A lid that has come unsealed on the shelf means throw it out.

Getting rid of a suspect jar of low-acid food or tomatoes

re-checked on NCHFP's live page.

• Still sealed: put it in a heavy garbage bag, close the bag, and put it in the trash.

• Unsealed, open or leaking: detoxify it first:

  • Wear disposable rubber or heavy plastic gloves.
  • Lay the jars and lids on their sides in an 8-quart or larger pot. Wash your gloved hands.
  • Add water without splashing, to at least 1 in over the jars. Cover the pot.
  • Bring to a boil and boil 30 minutes.
  • Cool, then throw the jars, lids and food in the trash.

• Clean up:

  • Mix fresh 1 part unscented household bleach (5–6%) to 5 parts water.
  • Wet every surface, tool, can opener and piece of clothing that touched the food, and leave it 30 minutes.
  • Wipe with paper towels and bag them.
  • Apply bleach again for 30 minutes, then rinse.
  • Wash everything and throw away the gloves.

Boiling before eating

• CDC's advice: boil home-canned vegetables, meats, other low-acid foods and tomatoes before eating. Boil 10 minutes below 1,000 ft, plus 1 minute for each additional 1,000 ft.

• USDA's version: says this is needed only if any step may have gone wrong.

• What we recommend: follow CDC.

• It doesn't fix a jar you know was under-processed. Throw that one out.

Symptoms of botulism

Symptoms usually start 18–36 hours after eating, but anywhere from 4 hours to 8 days:

• double or blurred vision, or drooping eyelids

• slurred speech

• trouble swallowing or breathing

• muscle weakness

It is a medical emergency. Get care right away.

Foods with no tested home-canning process

Freeze, refrigerate or dry these instead:

• Mashed or puréed foods:

  • pumpkin or winter squash (can 1-in cubes only), and pumpkin butter
  • mashed potatoes and refried beans
  • puréed vegetables or meats

• Fruit purées: banana, Asian pear, fig, tomato, melon, papaya, ripe mango or coconut.

• Summer squash and zucchini, except tested pickles.

• Dairy: butter, milk, cheese and cream, including in soups.

• Starches as thickeners: flour, cornstarch, rice, pasta or noodles. Clear Jel is allowed only where a tested recipe calls for it.

• Herbs and oils: pesto, and garlic or herbs in oil. Refrigerate and use within 2–3 days, or freeze.

• Others: bread or cake baked in jars, eggs, and dry-packed nuts.

Boiling-water canning:

• a large pot with a lid and rack, deep enough for 1–2 in of water over the jars

• a jar lifter, canning funnel and plastic bubble remover

• canning jars, new lids and bands

• bottled lemon juice or citric acid, and 5% vinegar

Pressure canning:

• a pressure canner that holds at least 4 quart jars, dial or weighted gauge, with a spare gasket

• a gauge test each year for dial gauges

• the same small tools as above

Recipe sources:

• the USDA Complete Guide to Home Canning (free PDFs at nchfp.uga.edu)

• NCHFP

• your state extension service

Cost and time:

• Cost: USDA says canning homegrown food may save about half the cost of store-bought canned food, not counting labor. Equipment prices weren't in any Tier 1 source.

• Time: a boiling-water load takes about 25–60 minutes overall; a pressure load about 55–100 minutes.

1. 1

   Water-bathing green beans, corn, potatoes or other vegetables. They must be pressure canned.

2. 2

   Skipping the acid in tomatoes or using fresh lemon juice.

3. 3

   Ignoring elevation.

4. 4

   Starting the timer before a full boil, or not restarting after the boil stops.

5. 5

   Not venting a pressure canner 10 minutes, or letting pressure dip without restarting the time.

6. 6

   Force-cooling the pressure canner.

7. 7

   Using an untested dial gauge.

8. 8

   Changing salsa recipes or thickening with flour or cornstarch.

9. 9

   Using an Instant Pot or other multicooker.

10. 10

    Reusing flat lids.

11. 11

    Storing jars in a hot garage or attic.

12. 12

    Tasting a doubtful jar.