Or you may have seen that recently published book about baking in jars, or that article in a swanky baking magazine complete with a gorgeously styled photo depicting a cake baked in a jar, or one of the many recipes on the Internet that say that “Yes! Yes you can bake in canning jars! And you can even seal the jars and then store them in the pantry!”
But can you? Surely if there are people selling these items, publishing books and articles about this practice, posting YouTube ™ videos even – then you can do it too, right?
No, you can’t. Or at least you shouldn’t. Here’s why.
First, canning jars (aka mason jars) are not designed for oven use. 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 a water bath or pressure canner, can create stress on the 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 water bath canner.) Canning jar manufacturers, such as Ball/Kerr, specifically recommend against using their jars in the oven (and in the microwave as well) . Knowing that jars have the potential to shatter, why risk your time, money, or even potential injury? Keep your canning jars out of the oven, and use an appropriate oven-safe vessel for all of your baking needs.
Second, and most important, is that canning breads and cakes in mason jars and storing them at room temperature is unsafe. Cake and quick bread recipes are usually low in acid and high in moisture, and together with the process of creating a vacuum seal by putting a lid on a hot jar (thus removing most oxygen), a perfect environment is created for many microorganisms to grow – including C. botulinum, the organism responsible for forming the toxin that causes botulism, a potentially fatal disease.
Putting a lid on a jar of baked goods after it comes out of the oven is not a true canning process, and while a vacuum seal may be formed as the contents cool, it may not be a good seal and not all of the oxygen may be removed. Any remaining oxygen in the jar would be would allow oxygen-dependent microorganisms – such as mold – to grow. This also goes for the process of putting a lid on the jar after the contents have cooled: air gets trapped in the jar, allowing microorganisms to grow.
Much research has been done at various universities to determine if canning cakes and breads can be done safely at home. To date, researchers have been unable to formulate a recipe for a palatable, safe product for home use. If you’ve seen commercial cakes or breads in jars available for sale and wonder why you can’t replicate this at home, it’s because reputable companies who make these products conduct safety tests for each specific recipe, have processing controls not available to home consumers, and often use additives and preservatives to keep the product safe.
So, please, no home canning of breads and cakes in jars! Use oven-safe bakeware, and refrigerate or freeze for longer storage. Do not eat any home-canned baked products that are given to you, nor purchase home-canned breads or cakes unless they contain anti-microbial additives and have been labelled in accordance commercial food requirements.
Be food safe, not sorry.