Onions are a staple ingredient in many recipes. Their savory flavor often is the finishing touch to your favorite meal. Canning and preserving onions leaves them soft but flavorful. Keep these onions in your pantry as an important ingredient for your favorite recipe.

Canning and preserving low-acid foods — such as onions — requires pressure canning to kill microorganisms that are harmful if not destroyed before ingesting the food. Pressure canning at 240 degrees kills the botulism bacteria. If this temperature isn’t achieved and the bacteria isn’t destroyed, one taste of this spoiled food can kill you. Simply boiling food on the stovetop will not kill any botulism and should not be considered a safety step.

Canned Onions

Canned onions are useful for any quick meal. They are great if eaten on a burger, heated and added to gravy, or just eaten as a condiment.

Preparation time: 20 minutes

Processing time: Pints and quarts, 40 minutes

Pressure level: 10 pounds

Yield: 20 pints or 10 quarts

20 pounds fresh onions

Canning salt

1. Prepare your canning jars and two-piece caps (lids and screw bands) according to the manufacturer’s instructions.

   Keep the jars and lids hot.

2. Peel and wash the onions. If you’re using large onions, chop them or slice them into 1/2-inch pieces.
3. Place the onions in a 12-quart pot, cover them with water, and bring them to a boil over medium high heat.

   Boil them for 5 minutes, or until they’re translucent.

4. Using a slotted spoon, remove the onions from cooking liquid (reserve the liquid for filling the jars) and firmly pack them into the prepared jars. Add 1/2 teaspoon salt to each pint jar or 1 teaspoon salt to each quart jar. Pour the hot cooking liquid over the onions, leaving 1-inch headspace.

   Release any air bubbles with a nonreactive utensil, adding liquid as necessary to maintain the proper headspace. Wipe the jar rims; seal the jars with the two-piece caps, hand-tightening the bands.

5. Process the filled jars in a pressure canner at 10 pounds pressure for 40 minutes (pints or quarts).

   Allow the pressure to return to 0, wait an additional 10 minutes, and then carefully open the canner lid.

   Use a pressure canner to safely process low-acid foods, including many vegetables.
6. Remove the jars from the canner with a jar lifter. Place them on a clean kitchen towel away from drafts.

   After the jars cool completely, test the seals. If you find jars that haven’t sealed, refrigerate them and use them within two weeks.

   Prior to eating or tasting, boil the food for 15 minutes. For altitudes over 1,000 feet above sea level, extend the boiling period 1 minute for each increase of 1,000 feet.

Per 1/2-cup serving: Calories 42 (From fat 2); Fat 0g (Saturated 0g); Cholesterol 0mg; Sodium 294mg; Carbohydrates 10g (Dietary fiber 1g); Protein 1g.

Source : http://www.dummies.com/how-to/content/preparing-canned-onions.html