What is Oven Canning?
Oven canning is a method of food preservation where the heat of your home oven is used in lieu of a water bath or pressure canner to seal jars of food. Directions for oven canning abound online, with many people reporting that they have oven canned foods for years and years without problems.
To can food in your oven, you fill up jars of food and place them in a warm (200 - 250 degrees Fahrenheit) oven for a certain amount of time. The idea is that the heat of the oven will sufficiently raise the temperature of the food to levels where harmful microorganisms will be killed. Unfortunately, this is not the case.
Hazards Associated with Oven Canning
Oven canning is considered dangerous by food preservation experts. Only water bath canning and pressure canning are recommended for home food preservation. According to the Agricultural Extension Service of the University of Tennessee, oven canning is “unsafe even for acid foods, because the temperature of the food never becomes hot enough to destroy food-spoilage organisms. Since the oven is not a pressure chamber (such as a pressure canner), food inside a canning jar in the oven can be heated no higher than the boiling point of water (212 degrees Fahrenheit at sea level), regardless of how high the air temperature is inside the oven. This is a basic law of physics.”
Remember that when you can foods at home you cannot assume a jar of food is properly preserved just because the lid has sealed to the jar. If you can foods in the oven your lids will most likely seal; however, the food is not safe to store at room temperature because harmful microorganisms are still present in the food. You must raise the temperature of the food you can high enough and for a long enough time to absolutely destroy harmul bacteria. If a jar of food is sealed but still contains live organisms the food will spoil.
For instance, the bacteria responsible for producing botulism toxin (Clostridium botulinum) actually thrives in a room temperature anaerobic environment, such as a jar of food. The toxin is completely undetectable in an opened jar of food - no change in color, smell, or taste of the food will alert you to the toxin’s presence.
Oven canning can also cause your canning jars to explode. According to food safety experts at Penn State University, “canning jars are not designed for intense dry heat and may explode resulting in serious cuts or burns.” Not to mention a mess of an oven!
To ensure the safety of the foods you preserve at home, do not attempt to can foods using your oven. Instead use safer methods such as a water bath, or pressure canner.
University of Tennessee Agricultural Extension Service, Methods of Canning
Penn State University, Unsafe Canning