Thursday, August 23, 2012

Oven Canning Is Dangerous - Do Not Do It

Over the past few months it seems there is quite a fad happening. People are turning to oven canning for food storage.  I had never heard of this, but did a little research.

It is a method by which one processes filled jars of food in the oven. Many years ago, people practiced oven canning, but it pretty much stopped with the invention of water bath and pressure canners.  There are valid reasons for this. 

For those of you who are considering canning in the oven,
you need to know that this is extremely unsafe and unreliable.

Why? Let me count the ways…
  1. Ovens are not consistent enough to be sure they reach the heat level needed to kill botulism.
  2.  Oven temperatures may vary.
  3. The dry heat produced in ovens does not penetrate the jars as quickly.
  4. Heat circulation is not the same in an oven as in a water bath or pressure canner. 
  5. Since the oven is not a pressure chamber (such as a pressure canner), food inside a canning jar in the oven can be heated no higher than the boiling point of water (212 degrees F at sea level), regardless of how high the air temperature is inside the oven. This is a basic law of physics.
  6. Heating foods in sealed containers causes a pressure buildup inside the container due to the expansion of food and entrapped air. If the metal band is screwed down too tightly, preventing the air to escape from underneath the lid, the pressure buildup will cause the food container to explode.
  7. It is unsafe even for acid foods, because the temperature of the food never becomes hot enough to destroy food-spoilage organisms.
  8. State supported extension services, utility companies, and canning jar/ lid manufacturers will not accept the liability of recommendations for oven canning!

What does all this have to do with dehydrating foods? 

  • Some sources suggest it is a good method of storing dry goods such as flour and grains.  
  •  Be cautious. This is a novelty and serves no practical application regarding the storage of dehydrated foods.
  • Oven canning dried things supposedly was intended to store beans, rice, flours, grains, and such. Not food you have dehydrated. 
Here are some problems with oven canning:
  1. The recommended temperature for oven canning is 250 degrees.
    1. One of the things we aim for is the least amount of processing possible.  More heat and high heat destroys nutrients.
    2. You have already preserved your food at the optimal temperature for long-lasting and nutritious food preservation. Why would you spoil that by cranking up the heat in canning jars?
  2. Canning jars are substantially more expensive than zip freezer bags. 
    1. One primary reason to dehydrate foods is economy.  Why would you spend more money on canning jars, rings, and lids, plus the additional cost of running your oven and heating your home when it isn’t necessary? Want to spend money needlessly? Send it to me!
  3. If you want to store your food in jars, go ahead.
    1. Simply put a lid on the jar and screw the ring down. That’s all you need. It works perfectly for things you will use over the next six months or a year.
  4. If you really, really, really MUST store your food in jars, most vacuum pack machines have an attachment for canning jar lids. 
    1. You can seal them perfectly without the damage to nutrients caused by over-processing and extended higher temperatures. Additionally, as long as the lids and gasket have not been damaged, you can re-use and re-seal the jars as needed.
  5. Are you planning on long-term storage?
    1. Instead of investing in canning jars, invest in a vacuum pack machine.  Your food will be lightweight, easy to transport (should an evacuation emergency be necessary) and take up substantially less storage space.
  6. See my post calledThis is Really Important” for more information on the problems of storing food in canning jars. 

Here are some links to tell you more about it:
Linda’s take on oven canning dehydrated foods:
Don’t be penny-wise and pound-foolish! *

 * That being said, this is my personal opinion based on a little prudent research.  Take for what it’s worth.


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