Is Baking in Canning Jars Safe?

And why would people want to?  Actually, there are a lot of reasons.

1. Well, because it's a novelty.
2. The half-pint jars are just cute, perfect for making single-serving casseroles or pot-pies and all kinds of desserts.  Check out Pinterest and you'll see what I mean.
3. The wide-mouth half-pints are the size of ramekins.  You could put a half-dozen in a Dutch oven.  Because taking a bunch of canning jars camping is such a good idea.  
4. Most preppers have a lot of canning jars, and we're going to be re-purposing canning jars, especially if and when we run out of lids. 

As far as the safety goes, we've got a couple of issues to address.  Is the food baking in canning jars safe to eat?  Is the jar itself safe for baking in?  And what about the lids and bands?

So to address the first issue, yes, the food baked in canning jars would be safe to consume, assuming that it's eaten within a day or so.  However, there is another issue to consider.  Baking bread in canning jars became popular among prepping-type women about a decade ago.  It was promoted as a way to prepare bread in advance of a disaster.  The idea was that this supposedly shelf-stable bread would be good to consume up to a year after it was baked.

Except for one little problem.  It's called botulism.  Baking bread in a canning jar and then capping the jar, either right after removing it from the oven or after it cools a little, creates the perfect conditions for botulism to grow and thrive--low acid food in a moist, low-oxygen environment.  Did you want a little death sprinkled on your toast?  While the oven temperature may be far above the 250 degrees required to kill the bacterial spores responsible for producing the botulism toxin, the interior of the bread dough usually doesn't get above 200 degrees.  Even if it did reach 250 degrees, without a lid on, botulism spores could settle right in during the cooling process.  (Botulism spores are found in abundance in the soil.  However, most cases of infantile botulism arise from spores carried by dust in the air.)  It's just not worth the risk.[1, 2]

If the bread (or any other food) were to be consumed right away, it would be safe, if we didn't have other issues at play.

But we do.

So for the second issue, is the jar itself safe for baking in?  Actually, according to the good folks that make Ball and Kerr canning products, the jars are not safe for baking.  The glass is annealed glass.  Tempered glass, like what Pyrex is made of, is designed to withstand thermal shock.  Even if tempered glass is exposed to a serious thermal shock and breaks as a result, it breaks into pieces that are more blunt and less likely to injure a person.  Annealed glass, which is what canning jars are made of, cannot withstand thermal shock as well as tempered glass.  A jar with cool or even lukewarm food in it risks shattering when placed on the pre-heated rack of an oven.  It can even happen as the oven heating element cycles on and off during the baking process.  And that jar may especially shatter when removed from the oven after baking.  The shards may go flying and inflict some serious injury.

Is the novelty of baking in canning jars or the cute dessert really worth the risk?  Especially if we don't even have good medical care?

And finally, we have the canning jar bands and lids, because some pretty cute desserts are also made with those.  They make a pretty handy post-apocalyptic miniature springform pan.  However, canning lids and rings are not recommended for baking, either. Well, if you ask Ball, that's what they say.  If you ask Bernardin, they say it's ok.  Now that they are all one big happy family, I can't find what they currently say.  

So there you have the word straight from the manufacturers and cooperative extension offices.  As with everything, we've got to weigh the advantages and disadvantages and make our own decisions.  The botulism risk is real.  I'd never eat bread baked in a canning jar more than two days previously.  I'd have to question the safety of eating anything prepared by someone who bakes bread in canning jars for long-term storage.  As far as the safety of using canning jars as bakeware goes, well, at least the person isn't going to kill me by doing it.  Would I do it myself?  It's possible.  For all the cool pics of baking in canning jars on Pinterest, I'd think we'd hear more about exploding jars if it happened a lot.  As far as the canning lids and bands go, well, I think dealing with all the grooves would be a major hassle.  It's not for me.

For further reading:
Safety of the food baked in canning jars
[1]https://extension.usu.edu/tooele/files-ou/food-preservation/FN-FS_250_10.pdf
[2]https://www.clemson.edu/extension/food/canning/canning-tips/36cakes-breads.html

Safety of using canning jars as bakeware
[3]https://www.freshpreserving.com/faqs.html
[4]https://www.countryliving.com/food-drinks/advice/a43870/can-you-bake-in-mason-jars/

Safety of using canning lids and rings as bakeware
[5]https://www.healthycanning.com/baking-in-canning-rings

4.13.23