A pressure canner is a large pressure cooker that is optimized for canning. The principle behind pressure cooking is actually quite simple. Normally, when you boil water at sea level, it rises to 212 degrees Fahrenheit (100 degrees Celsius). At this point, it turns to steam. What this means is that if you are boiling something in water, it will never heat up past 212 degrees. You can boil water for as long as you want, but it will never get hotter than that. Instead, you will simply make more and more steam.
Steam, however, can get very, very hot. In normal cooking, though, it disperses before it gets a chance to do so. Pressure cooking, however, is different. A pressure cooker traps steam. The steam expands as it gets hotter. This puts more pressure on the water. Water that is under pressure can actually get hotter than 212 degrees before turning into steam.
What does this mean? First, since you are trapping the steam, heat in a pressure cooker doesn't escape through steam as much as it does in normal cooking. This means that superheated steam does much of your cooking for you, and you are using less energy. Second, it means that food cooks very quickly in a pressure cooker, since steam is very energetic and will cook your food from all sides. Third, it means that it cooks food at a high temperature, which allows you to very quickly kill bacteria.
It is this last point which makes pressure canners feasible. Cooking food products at 250 degrees for three minutes will kill bacteria that can not only make food go bad, but be dangerous to your health. This is easy to achieve in a pressure canner. Normally, you use pressure canners to preserve food in Mason jars. Mason jars have thick glass walls, a flat lid, and a screw-on ring that holds the lid down. The dimple on Mason jar lids lets you know whether or not your jar has properly sealed.
Pressure canners come with a variety of options. Some notable brand names are Mirro, Presto, and the All American Pressure Canner. Typically, pressure canners are not only larger than other pressure cookers, but they also have thicker walls. Some of them come with racks to hold Mason jars inside of them. Some have gauges which allow you to Pressure canners come in a variety of sizes. In addition to being rated with a volume (usually between ten and thirty quarts), they are also usually rated with the number of pint or quart jars that they will hold.
Pressure canners, due to their large size, can also be used as stock pots. It is easy to make excellent pressure cooked stocks, soups, sauces, chili, or stews in an hour or so that would normally need to cook all day. Home pressure canning is also a remarkably thrifty art that has gained renewed popularity over the last few years. It allows you to preserve your fresh fruits and vegetables from different seasons so that you can enjoy them year round.
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All American 921 21-1/2-Quart Pressure Cooker/Canner
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Presto 01781 23-Quart Pressure Canner and Cooker
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