Canning Basics: Canning jar manufacturers specifically recommend against using their jars in the oven. 

Baking in canning jars (aka mason jars) is an unsafe practice, despite those cute pictures of miniature pies and cakes you see on the internet, especially around the holidays. Why? Canning jars are not designed for oven use, and canning jar manufacturers specifically recommend against using their jars in the oven. 

Canning jar glass (made from lime, soda, and other materials) is annealed, and annealed glass is not as strong as tempered glass. Oven heat, which differs from the heat produced in boiling water and pressure canners, can create stress on a jar, causing it to break into sharp pieces. And no, putting a pan of water in the oven along with the jars does not replicate the environment of a boiling water canner.

As for “oven canning,” putting a lid on a jar after it comes out of the oven is not a true canning process. While a vacuum seal may be formed as the contents cool, it may not be a good seal and some oxygen may remain in the jar – which would allow certain microorganisms, including mold, to grow. As for products such as breads and cakes, these tend to be low in acid and high in moisture. Along with the low-oxygen environment created by sealing the jar, this is the perfect environment for C. botulinum (the organism responsible for producing a toxin that causes botulism, a potentially fatal disease) to grow. 

In summary:

• keep your canning jars out of the oven!
• use appropriate oven-safe vessels for all of your baking needs
• refrigerate or freeze baked goods for longer-term storage
• do not eat any home-canned baked products that are given to you
• don’t purchase breads or cakes unless they contain anti-microbial additives and have been labelled in accordance with commercial food requirements

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Last updated July 2025