If my one goal in writing these posts is to keep those who can safe, it would be remiss of me not to include talking about the dangers of oven canning. Ruth asked me to put this together since both of us find that there is a lot to say, experts to quote, and if I create this information we will have a link to say all we can on the subject in one click.
Since sometimes “I feel” that people question my integrity and authority about the amount of research and information that I gather in order to give an “intelligent” answer I have posted links and phone numbers for those of you who may “second guess” me to follow up on. I wanted to give you the “research and manufacturer’s voice” rather than 30 years of canning who says, “I’ve done it”, so that somehow makes it ok.
The question is simple, Is ovening canning or putting jars in the oven safe?
Jarden the manufacturer of Ball, Kerr, and Bernadin canning jars official position (800-240-3340) is oven canning, heating jars in the oven for canning, or using jars to bake is unsafe and not recommended. The jars were not made for this purpose. The unsafe condition is what is call Thermal Shock Breakage. The heat from an oven is a different heat than what is produced in a water bath or pressure canner. The breakage can occur during the heat process inside the oven or outside on the counter as they cool. This breakage could be anything from a crack in the glass where shards may be deposited into the jar and not observed by the canner or baker and end up in your food, to a full break of the jars possibly happening during handling and filling with your recipe.
In addition the representative agreed that based on the contents that you are canning or baking there is no way to be sure that you are completely killing all the microorganisms and making the jars shelf stable. With baking you are running the risk of botulism as the ingredients that you are using such as eggs, flour, and other non-cannable products will grow bacteria fairly quickly in a jar. You are then giving these products to friends and family that you are putting at risk.
In addition the University of Georgia (UGa) and National Center for Home Preserving states clearly; (http://nchfp.uga.edu/questions/FAQ_canning.html#7) “No. This can be dangerous because the temperature will vary according to the accuracy of oven regulators and circulation of heat. Dry heat is very slow in penetrating into jars of food. Also, jars explode easily in the oven.”
To make the question of actual temperatures more clear and what a jar is exposed to; if used for canning, in a water bath canner water boils at 212 degree F. No matter how long you boil the water it will never get hotter than 212. For pressure canning the temperatures will increase to 240-250 degrees F which is required to make sure that your low acid foods are penetrated and bacteria will cease to grow. In an oven you will be subjecting the canning jar to an additional 100 degrees F in a dry environment more than is “normal” in a wet environment.
The question for you is that enough information to deter you from using your oven as a medium for heating your jars. I hope so!
One additional Note that Kat brought up in the comments: “You see a lot of people out there that do what they call “Canning Dry Goods” That is not recommended either. You can heat dry goods in the oven in a shallow pan to kill any bugs or larva, and then store them in jars, but don’t heat them in the jars.”
If you want to keep your family safe DO NOT do cake or bake in your jars, perform any kind of “Oven Canning”, or heat your jars in the oven for the water bath or pressure canning process. If you have done it or are doing it you have just been lucky.
Thanks Ruth for suggesting this post. I feel better knowing it’s out there for people to read!