Fill and cap
Using a large spoon or ladle, put the produce (raw or cooked, depending on the crop) loosely into jars. Then fill the jars with either boiling water, pickling solution (for pickles), or sweet syrup or white grape juice (for fruit). Because produce will expand during the canning process, don't fill the jars all the way; instead, leave some headspace—or space between the contents and the top of the jar. (When food is forced out of the jar because of insufficient headspace, the problem it creates is more than just the mess it makes in the canner. Food that winds up outside on the jar’s rim or around the lid can harbor mold, which can break a seal and cause the canned food to spoil.) Most vegetables and fruits—either in pint or quart jars—need about a half-inch of headspace, but don’t assume that is always true. Headspace requirements change with the density, shape, and cooking characteristics of individual foods. Always follow headspace requirements in a recipe. And be sure to measure the space carefully—too much headspace can make it more difficult to seal jars.
With a soft plastic spatula, push down on the produce in each jar to submerge it under the liquid; then run the spatula along the inside of the jar to eliminate air bubbles. Next, use a damp paper towel to clean off the jar rims. Close each jar with a sterilized two-piece lid, checking the manufacturer's instructions to be sure it is not too tight or too loose.
Load the canner
Put filled, capped jars into a canning jar rack and then lower the rack into the canner by its handles, or use a jar lifter to insert individual jars into a rack that’s already in place in the pot. Position the jars in the canner so that they are not touching.
Canning uses heat to destroy molds, yeasts, bacteria, and other organisms that cause spoilage. How much heat is needed, and consequently what kind of canner to use (a boiling-water canner or a pressure canner), depends on whether produce is acidic or not. In general, boiling-water canners are used for acidic produce and are much faster; pressure canners are used for nonacidic produce and require longer processing times.
If you’re using a boiling-water canner, fill the pot about halfway with water—enough to reach an inch or two above the jars after they’ve been loaded into the canner. Preheat the water to about 180°F for hot-packed produce or 140°F for raw-packed produce to prevent the jars from cracking. Insert the canning rack and capped jars. Cover the canner and bring water to a steady, gentle boil, which must be maintained throughout the required processing time. (Do not start timing until the water starts to boil.) Because water boils at lower temperatures at higher altitudes, processing times may be longer (and higher pressures are likely to be needed for pressure canning). If you live at a higher elevation, check with your local Cooperative Extension Service agent for canning recipes adapted to your region.
If you’re using a pressure canner, follow the manufacturer’s directions, which will vary depending on the type of canner and the altitude. Generally, put 2 inches of hot water in the pressure canner, add the jars, put the lid on the pot, and increase the pressure before you start tracking processing time. When processing is finished, let the pressure drop before opening the canner and removing the jars.
Cool and check
Use jar lifters to gently remove the jars from the canner and place them an inch apart on a wooden board to cool. While they cool, the lid gaskets become firmly sealed to the jars.
After 24 hours, check the lids to be sure they are airtight. Push down on each metal lid: It should not give or spring back up. As a double check, tap each lid with the bottom of a teaspoon. A sealed lid will give off a high-pitched ring, not a thud. If any jar is not sealed, put it in the refrigerator and enjoy its contents for dinner. Once a jar is safely sealed, write the name of the contents and the date of canning on its metal lid with a permanent marker. Wipe off any food on the outside of the jar.
Store the bounty
To preserve vitamin content and discourage lid corrosion, find a cool, dark, dry, out-of-the-way place to keep your canned goods.
For more information and delicious recipes, here are two great resources on canning and preserving: