What is Oven Canning?
Oven canning is a controversial method of food preservation that uses low oven heat to process and seal jars of fruits, vegetables, and sometimes grains. It is typically not recommended by food safety experts for several reasons, including temperature accuracy and increased likelihood of contamination or spoilage. The process often involves a lot of guesswork or past experience. Reading up on the various methods and processes, as well as understanding the leading risks and expert recommendations, is essential before beginning.
“Dry” Oven Canning
When people talk about oven canning they are most often referring to “dry canning,” in which cans of prepared food are set in a warmed oven and allowed to process for a set amount of time. This method is quite controversial in the food community and is often harshly criticized as being dangerous and unsafe.
The theory behind dry canning is that cooks are able to kill any food-borne bacteria by slowly heating the food in glass jars. The oven is usually heated to around 200°F (about 93°C), and the jars placed on the oven’s racks and allowed to heat for 30 minutes to an hour. When the jars “pop” — that is, when their seals depress — they are believed to be closed off from contaminants, and they can theoretically be stored at room temperature for several years.
Food Safety Concerns with Dry Canning
Contamination is the main fear when it comes to dry canning. In order for food to be shelf-stable, it must be heated to a hot enough temperature that any latent bacteria in the food is killed off. The premise behind dry canning is usually sound, as a 200°F oven is generally hot enough to be considered sterile. Not all oven thermometers are accurate, however, and it can be tough for home cooks to know whether the external temperature is actually penetrating the jars.
There is no way for cooks to test the internal jar temperature without removing the lids and compromising the food. Any bacteria that remains in sealed jars can grow into toxins over time, which can cause serious food poisoning once the contents is eventually consumed. Sometimes spoiled food looks discolored or has an unpleasant taste, but not always.
Risk of Explosion
A more immediate danger of oven canning is explosion. Canning jars are not designed to be exposed to prolonged dry heat and have been known to crack or even shatter during processing. At best, this creates a huge mess; at worst, it can lead to severe burns, cuts, and infections.
Water-Based Oven Canning
Some of the downsides of dry canning can be avoided by using water. According to this process, jars are placed in a pan of water inside the oven rather than simply standing alone on the racks. This method is very similar to water bath canning, and while still controversial, tends to have fewer safety concerns.
The traditional so-called “water bath” canning method involves bringing a large pot of water on the stove to a boil, then submerging closed jars for a set amount of time. The boiling water creates both heat and pressure that sterilizes the food and forms a vacuum seal.
Setting jars in a similar water bath in the oven can achieve similar results, and often uses less energy. The jars do not always need to be submerged, either, as the heat of the oven combined with the steam from the water can produce a powerful seal in a shorter amount of time. Still, the practice is widely criticized as being far less precise than the standard water bath method, and home canners are advised to carefully weigh the risks against the perceived convenience when choosing one method over another.
I have made batches of jams, jellies, sauces, etc. from fruit as well as salsas, and tomatoes in the oven method for at least 20 years. This summer I have put up at least 14 batches of things with only two seals not sealing; both times I had not left enough head room so when the contents expanded the seal popped. I do sterilize all the jars first in water as well as all my Tools and do the snap lids in hot water for five minutes. Oven canning is easier because I can have them in the oven while I am making the next batch of sterilized bottles on the stove top. I have not even once had spoiled foods, exploding bottles, etc.
Oven canning is for dry goods only! Dry canning is a method of preserving from bugs and keeps dry goods from going stale: macaroni, noodles, flour, cereal, etc. It is not for vegetables unless they are dehydrated. There is nothing dangerous about it if it is done with the right products! Do not tell half the story!
I'm about to do my tomatoes and will use the over. New korean stovetops do not heat the water in a water canner quickly enough and we end up cooking the food: pickles. Knowing I can do my tomatoes the same way is great.
First: Canning in the oven should mean placing jars filled with food in a shallow container with water! Second: THE safety factor is whether the lid seals! If the lid seals, the food is good. Third: Anytime a lid does not seal (using ANY method of canning), when the lid is removed the smell will be the undeniable clue. Period.
I couldn't agree more. In Wales UK my mother canned everything in the oven (a Raeburn wood/coal stove, very unpredictable as far as heat was concerned) but everything turned out great and the two hour water bath at about 200 sounds right!
Just tried water bath canning, yuck! I learned the oven method 35 years ago. My Mother always did it that way. i have a copy of directions from Better Homes, canning in the World War II era. So pick your poison, I'll take oven canning any day. Never had any type of accident or illness.
I have canned in the over for years with no jar breakage or spoiled food. I use 250 and leave them for two hours just to be sure.
I find this a safe way to process food, and it sure doesn't heat up the house like a canner full of boiling water!
All the articles condemning oven canning concern dry canning, i.e. placing the jars on the racks.
My grandmother lived on a huge farm and their garden was about 10 acres. Every summer was spent canning. Since she did not own a pressure canner, she oven canned, but she did it a little differently.
She filled the regular boiling water canner with water as usual, but placed it in her oven and set the temperature to 250. Once the water had reached that point, she put her jars into it and set the timer.
Whether on the stove top or in the oven, the water is still going to hit 240, so I see no reason why oven canning this way would not be safe.
Between my mother and I, we have canned thousands of quarts of tomatoes in the oven for over 75 years. Using two-quart jars, a bushel can be done at one time. Very few jars have broken and temps exceeding boiling water are used. Have not used for any other food. Ball used to published a Blue Book that gave oven temps and time for all kinds of foods.
I have canned tomatoes in the oven for 53 years and have never had a jar break or any problem with them going bad, let alone had food poisoning.
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