The conventional way of processing food is to place them in jars which would be then put into water bath canners filled with water. This is done by immersing jars into boiling water, allowing the high temperature to kill the bacteria in it. However, when it comes to processing low acids food, a much higher temperature is needed, or else the bacteria in it will not be killed. Low acids foods refer to any food at or above the pH level of 4.6, such as red meats, sea food, poultry, and fresh vegetables. The temperature that can neutralize the bacteria is at 240 F, and it has to be maintained for some time. In order to get this done, the food needs to be put under steamed pressure. This can be achieved using pressure canners.
Pressure canners look like a pressure cooker, and can carry the functions of one, however, as its name suggests, it also cans. Modern day canners are built lightweight, with thin walls made out of either aluminum or stainless steel. Most have lids that fit in by twisting, and have a gasket attached to it so that the contents do not leak out, while others uses knobs on the lids that screw enables you to screw it down into the canner. With either the dial gauge, or weighted gauge type of canner, both are able to indicate how much pressure there is in the canner. These canners are usually able to fit one layer of quart sized jars or two layers of pint size jars.
As mentioned earlier, water bath canners need to be filled with water to work its magic. Pressure canners, on the other hand, rely on how much pressure is needed, which can be created by the amount of water you put in. The canner will then boil the water inside, which causes water and steam to fill into the area where the jars of food are placed. As the space is pressured, the temperature of the steam can be increased with heat compacted around all sides of the jars, thus, processing the food.