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Why Oven Canning is a Bad Idea

Why Oven Canning is Not Recommended - LivingHomegrown.com

I figure for every question I get from my readers – via comments or emails – there may be a few others with a similar question.

But when I get one question over and over, I know it’s time to write up that discussion as a blog post so that everyone can benefit from the information.

Such is the case with today’s post.

Why Oven Canning is Not Safe - LivingHomegrown.com

What is Oven Canning?

I have been asked several times lately about “oven canning”

  • Is it safe?
  • Have I ever done it?

In case you are not familiar with the term, Oven Canning is when you place jars of preserves in the oven to “process” them rather than processing them in a water bath.

A typical reader question goes like this:

“I’m wondering if it is okay to process in the oven instead of the water bath. I’ve heard of people placing the filled jars into the oven at 220 degrees for 15 or 20 minutes. It seems like this would work because you are placing the jars in the same temperature for the same amount of time. And it sounds easier. What do you think?”

I’m so happy to answer questions like this because it gives me an opportunity to not only squelch some bad information going around the internet, but to also explain the reasoning and the science behind the USDA recommendations on this matter.

I believe that by understanding the “why”, we care better equipped as canners to make these safety decisions on our own.

First – The Big Picture:

I know it sounds logical that this technique would work and yes, some people do it even though they know it is considered dangerous. Back in the day, I even tried it myself.

But canning recommendations have changed and I know better now. I would not do this today.

Let’s first look at the big picture here. When I can, I want to be sure that what I feed my family is as safe as I can make it.

If I’m going to the trouble to can in the first place, I don’t want to use any technique that is questionable. Using questionable methods pretty much defeats the purpose of working toward healthier food for my family.

I’m figuring you probably feel the same way.

That said, if I can look at the science behind a method or find testing that demonstrates the safety of something against USDA policy, I might consider it.

For example:

I do use Weck canning jars occasionally even though they are not recommended by the USDA.

But there is a big difference here:

  • Weck jars are tested and recommended via European countries.
  • The USDA is not recommending against them.
  • The USDA simply has not taken the time to test and recommend themselves.

Oven Canning is different.

The USDA strongly recommends against the practice of oven canning.

And Master Food Preservers are taught to preach against it. Here’s why:

Why Oven Canning is Not Safe - LivingHomegrown.com

Why Oven Canning is NOT Recommended:

1) Dry Heat: Although the oven is set to 220 degrees, there is a difference between dry heat (oven) and wet heat (water bath). The heat penetrates the food at a different (slower) rate. There are no tested standards for how long something must be baked in a home oven to reach the proper temperature internally to kill bacteria and create the proper vacuum seal vs. when we just cook the food in the jar. If the entire contents did not reach the proper temperature, the mold and bacteria are not completely killed. And we know for sure that a straight swap out of time is not long enough. The big problem is that no one knows for sure how long is long enough without baking the contents.

2) Thermal Shock: There is a risk that the jars can break – especially with the lids on and especially when removed from the oven. The jars are not tested or manufactured for this type of dry heat canning. And thermal shock is more likely with dry vs. wet heat. This could be dangerous if they crack or explode while you are removing them from the oven.

3) Vacuum Seal: Some people bake the jars and then put on the lids as they come out of the oven. The same problems mentioned above apply. But when doing it this way, you are more likely to get a weak vacuum seal (not as strong of a vacuum as water bath). Also this two-step process allows more entry points for surviving bacteria – especially mold.

NOTE: Although mold is not poisonous, it is a carcinogen and should be avoided.

Here’s the Thing:

I realize that despite the warnings, a small percentage of people still do this. And no, there are not 100’s of people rushing to the emergency room with shards of glass in their eye from jar explosions. (But I have heard stories of broken jars).

My question is this: Why choose oven canning over water bath processing when the results and  safety are questionable (beyond the possibility of broken jars)?

Oven canning is not easier or faster than water bath processing. In fact, it should take longer because the dry oven heat should be given more time than wet heat.

Perhaps it boils down to people not believing the safety concerns or they just feel lucky. They are free to make the choices that they feel most comfortable with.

For me, the whole point is to feel confident in what I am feeding my family. So, I do not oven can. As a trained Master Food Preserver, I do not recommend it.

What are your thoughts on this?

Please let me know in the comments.

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About the Author:

Theresa Loe is the founder of Living Homegrown® and the Canning Academy® and is the Co-Executive Producer & Canning Expert on the national PBS gardening series, Growing A Greener World®. Theresa homesteads on just 1/10th of an acre in Los Angeles with her husband, two teenage boys and several disorderly but totally adorable chickens. Learn more about Living Homegrown here and about the Canning Academy here.