Oven canning is a type of canning in which jars are filled with food and then baked in the oven for a set period of time. This method of canning is not recommended, and it can in fact be extremely dangerous. There are a variety of reasons why oven canning is unsafe; it is much better to use a boiling water bath or a pressure cooker for canning, as these techniques are time tested and very effective when performed properly.

The theory behind oven canning is that by heating the food in the oven, the cook will able to kill any harmful bacteria which could be lingering. Therefore, the oven is heated to around 200 degrees Fahrenheit (93 degrees Celsius), and the jars are placed inside on racks and allowed to heat for 30 minutes to an hour. After being allowed to cool, the jars could theoretically be stored in a pantry or under refrigeration for several months.

However, oven canning is not an effective food preservation technique, and it can be extremely dangerous. The immediate danger of oven canning is explosion, because canning jars are not designed to be exposed to prolonged dry heat. If the jars are old, too full, or improperly sealed, they can fail catastrophically, spewing food and glass everywhere. At best, the oven will be filthy and possibly damaged; at worst, oven canning can cause severe burns and cuts from shards of glass.

The dry heat of the oven is also not effective for food preservation. It rarely penetrates all the way to the middle of the canning jar, and there is no way to test the internal temperature without breaking the seal and compromising the food. As a result, bacteria may remain in the food, and it will happily grow and flourish while the food sits on the shelf, potentially causing food borne illness when someone eats the improperly canned food.

It is difficult to control the temperature in an oven, especially at low temperatures, and the heat circulation is often poor. Therefore, it's difficult to know if the oven is even at the “right” temperature for oven canning, let alone whether or not the heat has penetrated into the food cooks are trying to preserve. You should not attempt to preserve food using this technique, and you should certainly not consume food which has been oven canned.