Canning Basics

The two methods

All foods are canned by one of two methods:

1. Hot water bath is used for acid foods. These include all fruits, tomatoes, sauerkraut, and most foods to which vinegar has been added, such as most pickles and relishes.
2. Steam pressure canner is used for foods containing little acid. These include vegetables (except tomatoes), meats, seafood, and mixes of food that include some low-acid foods.

All foods, acid and non-acid, contain enzymes and can harbor molds and yeasts, all of which will cause food to spoil. All of these can be inactivated or killed by the heat of the boiling water bath.

The steam pressure canner is used to destroy another threat to canned food: bacteria and their by-products, including Salmonella, Staph, and Botulism. These harmful bacteria are not a problem in high-acid foods, so there’s no reason to use the high-temperature method for them. They thrive in low-acid foods and aren’t destroyed by the 212°F of a boiling water bath, but they succumb to a recommended period of 240°F heat. So the steam pressure canner must be used for low-acid foods.

Raw pack and hot pack

Raw pack or cold pack: putting uncooked food into a jar to which a hot liquid is added.

Hot pack: putting food that has been cooked to some degree into the jars. Hot pack sometimes needs less processing time since the food is already partly cooked. Sometimes it takes as long or longer because of the denser pack. Instructions for each food explain which packing method to use and the processing time required.

If this is your first time

• Start small. Six quarts of tomatoes or a half-dozen jars of jam or jelly are plenty for a first try.
• Be prepared with everything you need: jars, fresh lids, and all the equipment, including a pressure canner with a gauge that’s been tested if you’re pressure canning. Most important, produce at the peak of perfection, ripe but not too ripe.
• Have a large cleared area to work in. Canning takes lots of space.
• Have more time than you’ll need. Think it’ll take an hour? Give yourself two and feel no pressure.
• Canning is a lot like baking bread or following a complicated recipe. It gets a lot easier the second time you do it.

Checklist & safety

Canning is quite a bit different from ordinary cooking. When you cook, you can be adventuresome and add or leave out ingredients as you see fit. When you’re canning, experimentation can be downright dangerous. Times and temperatures have been worked out very carefully and must be followed to the letter. Too little time or too low a temperature means you’re not protecting the food against bacteria, enzymes, molds, and yeasts. Too much time or too high a temperature can needlessly destroy nutrients and damage the taste.

So always follow directions and recipes precisely. Botulism and other food poisoning is very serious. Read carefully before you begin.

• Inspect your jars. All jars should be free of cracks or nicks in the rims. Damaged jars can cause food to spoil. Make sure you have enough jars for the job.
• Check jar tops. If you’re using two-piece vacuum caps and lids, make sure you have enough, that they’re new and rust-free, and that the screw bands are rust-free too.
• Use completely clean equipment. If you’re pressure canning, check that the gauge on your canner works properly.
• Wash and rinse jars thoroughly. Use dish detergent and rinse well. Keep jars in clean, hot water (or in the dishwasher) until used.
• Make sure lids and bands are clean. Follow the manufacturer’s instructions.
• Remove blemishes from produce. Cut out dark spots or anything that doesn’t look right and fresh.
• Scrub produce. Thoroughly wash and rinse it.
• Have enough room to work. Crowding causes spills and breakage.

Boiling water bath canning

This method is easy and popular. Use it only for high-acid foods: fruits, tomatoes, and some foods with vinegar added. It works with both raw-pack and hot-pack filling.

You’ll need a boiling water bath canner: a big kettle with a tight-fitting cover and a metal basket that holds the jars off the bottom so hot water can circulate underneath. The kettle must be deep enough that the jar tops are covered by at least an inch of water, with at least another inch of space above the water. Most quart jars are 7 to 7½ inches tall, so the canner should be 12 or more inches deep. The same kettle can be used for jams, preserves, and marmalade.

1. Fill the kettle half full of water and bring it to a simmer. Heat a second, smaller kettle of water.
2. Place raw or hot-packed food in clean, hot jars, leaving the recommended headspace. Salt if desired; it isn’t necessary for preservation.
3. Run a plastic bubble freer around the inside of the jars to release air bubbles.
4. Wipe the top of each jar with a damp cloth if your syrup contains sugar, or a dry towel if not, so no particles interfere with the seal.
5. Center the lid over the mouth of each jar and screw the band down firmly.
6. Lower the jars into the boiling water with a jar lifter. Make sure jars aren’t touching.
7. Add boiling water from the other kettle to cover the jars by one or two inches. Put the lid on and start timing.
8. When the time is up, remove the kettle from the heat and lift out the jars. Leaving them in longer overcooks the food.
9. Set the jars on a cake rack or towel in a draft-free area. Don’t knock them together; hot jars shatter easily. Don’t tighten or loosen the screw bands. Leave them undisturbed for twelve hours to cool.
10. Test the seal. If it isn’t good, refrigerate and use the food soon, or reprocess within 24 hours with a new lid. The most common causes of a bad seal are food caught between lid and rim, and cracks on the rim.
11. Remove the screw bands, wipe the jars clean, and label them with the food, where it came from, and the date.
12. Store in a cool, dry, dark place. Plan to eat canned foods within one year.

Boil all home-canned vegetables in a covered saucepan at a full rolling boil for 10 minutes before serving; spinach and corn for 20 minutes. If the food looks spoiled, foams, or has an off odor during heating, destroy it.

Pressure canning

1. Place the basket or rack in the canner. For hot-pack foods, add boiling water (see the table below for the amount) and set on low heat. For raw-pack foods, add the same amount of hot but not boiling water, and don’t let it simmer.
2. Fill clean, hot jars with food, leaving the recommended headspace. Add salt if desired. Release air bubbles with a bubble freer and adjust the lids.
3. Set each jar upright on the rack. Jars must not touch each other or the bottom of the canner, so steam can circulate freely.
4. Put the cover on and lock it securely.
5. Turn the burner to the highest heat with the vent open so steam flows freely. Vent for 7 minutes for canners up to 8 quarts, and 10 minutes for larger canners.
6. Close the vent: place the pressure regulator on the vent pipe (weight-control canners) or close the control valve (gauge canners).
7. Let the pressure build to 10 pounds for canning at 240°F. On dial-gauge canners, turn the heat to low when the dial is almost at 10 pounds. On weight-control canners, reduce the heat when the control jiggles vigorously; it should jiggle two or three times a minute.
8. Avoid rapid temperature changes, which cause pressure swings and force liquid out of the jars. Start timing as soon as the required pressure is reached.
9. When time is up, turn off the heat and let the pressure return to zero on its own. Don’t run cold water over the canner, remove the regulator, or open the valve early.
10. At zero, slowly remove the regulator or open the valve. On weight-control canners, lift the control slightly with a fork; if steam spurts out, wait longer.
11. Unlock the cover and lift it off far edge first, so you’re shielded from the steam.
12. Set the jars on a rack to cool. If using two-piece lids, don’t tighten the bands. When cool, test the seals, remove the bands, wipe and label the jars, and store them somewhere cool, dry, and dark.

Weight-control canners: use 15 pounds at 2,000 feet and higher.

Preserving tomato products

Tomatoes have traditionally been canned in a boiling water bath (212°F), but pressure canning gives a higher-quality, more nutritious product for some tomato foods. Recipes that list only pressure-canning times have so many low-acid ingredients that they are only safe in a pressure canner at the given pressure.

Acidifying tomatoes

Because tomatoes have pH values close to 4.6, take precautions to can them safely. Select only disease-free, preferably vine-ripened, firm fruit. Do not can tomatoes from dead or frost-killed vines.

Add acid to whole, crushed, or juiced tomatoes whether you use a water bath or a pressure canner: 1 tablespoon bottled lemon juice or ¼ teaspoon citric acid per pint; 2 tablespoons bottled lemon juice or ½ teaspoon citric acid per quart. Add it right to each jar before filling. If it tastes too acidic, add a little sugar. Four tablespoons of vinegar per quart (2 per pint) can be used instead, though it may change the flavor.

Tomato-vegetable recipes

Unless a tested recipe is used, all tomato-vegetable mixtures must be processed in a pressure canner, following the directions for whichever vegetable in the mix needs the longest time. When the exact amounts below are used, these mixtures can be processed using the times given.