Water-bath canning (also called boiling-water canning) is a way of preserving food in jars by submerging the jars in a pot of water and boiling them for 10 to 20 minutes (depending on the food). This method is used for high-acid foods, such as fruits or pickled vegetables. For low-acid foods, such as green beans or mushrooms, water-bath canning is not sufficient to kill toxin-producing bacteria. These foods need to be processed in a specialized pressure cooker. (For more information on pressure canning, go to the Ball jar site where you can watch a tutorial online or download a pdf version.)
How to Preserve Your HomemadeRhubarb-Ginger Jam
1. Wash two pint-size canning jars, their lids and screw bands in hot soapy water. Rinse and drain. (The typical jars used in canning have two-piece lids: a flat top that sits right on the rim of the jar and a threaded piece—the screw band—that screws onto the jar top to hold the lid in place.)
2. Place the jars on a rack in a water-bath canner.* Add water to the canner and to the jars until the jars are two-thirds full. Cover the pot and bring the water to a simmer over medium heat. Do not boil. Keep the jars hot until you're ready to fill them.
3. Meanwhile, bring the jar lids to a simmer in a small saucepan. Keep the lids hot until you're ready to close the jars. (The screw bands do not need to be heated.)
4. After you've cooked the jam and are ready to fill the jars, take a jar out of the canner; pour the hot water out of the jar back into the canner. Ladle the jam into the hot jar, leaving 1/4 inch of headspace. Slide a rubber spatula between the jam and the jar sides a couple of times to release any air bubbles.
5. Wipe the rim of the jar clean in case you spilled jam on it. Place a hot lid on the jar, then place a screw band on top. Screw the band down only as far as you can by turning with your fingertips. Do not over-tighten.
6. Return the jar to the rack in the canner. Repeat with the other jars. When all the jars are back in the canner, add more water if necessary so it covers the jars by at least 1 inch. Cover and bring to a rolling boil over high heat. Time the canning (10 minutes for this recipe but it will vary depending on what you are canning) from this point, and keep the water at a full boil.
7. When the jam is ready, turn the heat off and remove the lid of the canner. Let the jars sit for 5 minutes in the water, then carefully lift the jars (try not to tilt them) and place them on a towel in a draft-free place to cool undisturbed.
*If you don't have a water-bath canner (also called a boiling-water canner), you can use any pot that is 3 inches taller than the jars you will be using. You will also need a rack (like a wire cake-cooling rack) that can fit in the bottom of the pot, and ideally a specialized pair of tongs for lifting heavy jars out of hot water.
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