Canners: Oven Sterilizing/sealing a good idea?

I was reading a new canning book today (Blue Chair Preserving) and the author recommends sterilizing jars and lids for canning jam by heating them in a 250 degree oven for 30 minutes. That seems safe enough, but then she also recommends using a hot oven to seal the jars. Has anyone done this? Is it safe and effective? What about for tomato products or pickled foods (anything you'd normally do in a standard water bath canner)? It's intriguing as my canning rack causes some issues and I'm seeking a better one that keeps jars actually in their rightful place. Also could be good for odd-sized batches.



Diana B. August 26, 2012
A canning rack is preferable to a towel in the bottom of the canner because towels don't allow water to circulate around the entire jar the way a rack does. You can use upside-down jar lid bands in lieu of a rack if you have a collection of old ones that have gotten dinged or slightly rusty (and what canner doesn't?).
jamcook August 26, 2012
you can also put aa old clean towel in the bottom of the canner to keep things from rolling around. You can also do this if you are using a hot water bath for custards or other things in small ramekins or cups.
chefsusie August 26, 2012
Just a thought. My small jars bounce around too. I place a rolled up piece of aluminum foil in the water bath to fill up the gaps. Works beautifully.
Raquelita August 26, 2012
Brilliant! This whole thread has been interesting, and chefsusie's advice is quite practical. I know I can also fill up with dummy jars, but those little guys are pesky. I will try the foil and resolve to find a more supportive rack.
Diana B. August 25, 2012
Thank you, ChefOno, for your clear and cogent explanation. I learn something every time you weigh in on the science behind a method!
peggy D. December 20, 2017
I have used her method for jams and tomato-pepper relish without any prroblems...I'm sure the sugar content helps
ChefOno August 25, 2012

The reasoning / science behind abandoning oven canning is manifold:

As suggested, actual oven temperatures can vary considerably from the set point, both due to inaccuracy of their thermostats and from the way they function. Ovens cycle on and off to regulate temperature and there can be a considerable variation between the temperature at which they turn on and when they turn off. The set point can represent the high, low or average temperature -- or none of the above in many cases. In contrast, water boils at a consistent point with simple, known adjustments for altitude.

Transmission of heat through air is inefficient compared to water or steam. Put your hand in a 250F oven and then put it in boiling water if you want a quick demonstration of the principle. So a 250F oven will not heat food to the same temperature as a boiling water bath unless it were to remain for a considerably longer time. And even then it wouldn't if the surface of the food is left exposed due to heat lost through evaporation. Canning requires known times and temperatures to be safe.

Radiated heat from direct exposure to an oven's heating coils has shattered many a jar causing injury, loss of food and one hell of a mess. Blue Chair's desire to return to a simpler time may give some people a warm and fuzzy feeling but could very well produce fuzzy food and a case of botulism in the process.

SKK August 25, 2012
Thanks, ChefOno. Well said. Thank you for the full explanation.

Regarding returning to a simpler, fuzzy time for canning, I don't think it ever existed. When my Gram canned and Mom helped her. with me as a younger person in the background, it was hard, hard work. We didn't have dishwashers, we had water boiling everywhere - to sterilize jars, to heat whatever we were canning, to have the lids staying warm. When we were at my Gram's, there was no running water. We pumped well water (it was so good) and carried it.

We are blessed with what we have today. And blessed to have this amazing knowledge base to safely preserve great foods.

Thank you again for your great explanations!

jamcook August 25, 2012
Don't sacrifice all that work by using a method that sounds questionable to so many of us , and to me, sounds like more work than water bath canning.
Lizthechef August 25, 2012
When I have a canning question, I go to the Ball site and click on "safe canning procedures". I also add a link there when I do a post on my site that involves canning. This is a better idea than to just say "Process according to safe canning procedures". That oven method is NOT recommended, by the way.
smslaw August 25, 2012
I'd be interested in some scientific evidence one way or another. I would think canning jars placed in a 225 degree oven should heat the food as much as in a 212 degree boiling water bath, but maybe I'm missing something. Oven temps are notoriously inaccurate and unstable, so one concern is that a 225 degree oven will result in temps at the jars that may sometimes be lower than the boiling point.

I do use the Blue Chair method for jams. I love the book.

I just canned some tomatoes today, using the traditional boilingwater method. I do always use the oven to sterilize the jars.
SeaJambon August 25, 2012
smslaw - I don't know about "scientific" but the National Center for Food Preservation (see Chef Ono's note above) is the ultimate authority for safe preserving (including canning) in the US and they do NOT recommend the oven method. Your thoughts about the variability of oven temp's (and even how much they fluctuate) is probably one reason and there may be others.
Raquelita August 25, 2012
Thanks for the reassurance! I'll stick with the water bath--preserved foods would be a shame to lose to spoilage...sort of defeats the whole purpose. (The canning rack is too big for the little jars so it's a lot of fumbling around. Works great for 7 quarts...I just need to make that next purchase of a small-jar rack)
SKK August 25, 2012
In agreement with ChefOno. I have been canning, dehydrating and preserving for years and learned from my grandmother and mother as well as taking classes. Don't know why the author of the book would make the recommendations she did. Real research has been done by universities and state schools, along with Ball. So follow the directions of the manufacturers and the excellent link Ono provided.

Don't know what problems you are having with your canning rack. I have two sizes of canners, one for quarts and the other for pints and half-pints. Maybe your rack is too big for your jars?


Voted the Best Reply!

ChefOno August 25, 2012

Don't do it.

Recommended by Food52