May 7, 2011

Canning :: Water Bath Vs. Pressure Canner

I made chicken stock yesterday, and was wondering if I could can it, rather than putting it in the freezer like I normally do. A quick look in my Ball Home Preserving book showed that yes, indeed, I could can chicken stock. (Which I'll share later.)

But it had to be done in the pressure canner, rather than just a water bath.

I never really knew why you had to do some things in the pressure canner while others could just be boiled until I started getting interested in canning things myself.

So here is what I've learned, just in case anyone else is curious.

Naturally high-acidity foods - like tomatoes and fruits (or recipes with tons of vinegar) -  can be water bathed because the acid will kill the botulism spore that would otherwise invade your body like a S.W.A.T team can swarm the house of an arms dealer on a coke bender. A water bath will heat up sufficiently for the rest of the germs the acid doesn't get.

Low-acidity foods - like vegetables and meats - need to be pressure canned because they don't have the added germ killing power of the acid, so they need the extra heat. Regular water-in-a-pot canning can't get hot enough to kill the beasties just by itself, since these foods need to be heated to 240 degrees to kill the botulism spore, and water only boils at 212 degrees (if you're at sea level. Lower if you're elevated higher than that). But by adding the extra pressure the water can super boil (basically), ensuring that your home made goodies are fine and safe to eat.

From the Ball Book of Home Preserving:
To safely preserve low-acid foods, a device called a pressure canner must be used. This equipment has a lid that is locked in place. As a result, when water in the canner is heated to the boiling point, it produces steam faster than the steam can escape from the vent and thus pressurizes the canner. The pressurized steam creates hotter temperatures, which surround the jars and cause the temperature of the food within to rise to 240 degrees.

So, be sure to check your recipes and follow whichever method they tell you to use. And if you're unsure of how to can your goodies, just remember that High acid = low temp, and low acid = high temp.

Because Botulism is never in fashion.

Happy Canning,


Kessie said...

"otherwise invade your body like a S.W.A.T team can swarm the house of an arms dealer on a coke bender."

I lol'd so much at that one.

I always wondered why some things you had to waterbath vs. pressure canning. I always thought it was a matter of preference.

Does it say anything about when you just turn jars of jam upside down to seal them and not waterbathing them? I've seen some controversy about that. Mom and I always just inverted our jam jars and never had sealing or mold problems, but people go around and around about it.

Meg said...

Kess: The heat processing allows for a tighter seal on the jars, that you can't achieve with turning them upside town - even if they seem tightly sealing. Also, the high heat is what's needed more than the sealing itself to kill the bad stuff, which obviously can only be done with boiling (or pressure canning).

From the book "Heat-processing home-canned food is not optional! It is essential for destroying food spoilage microorganisms and creating an adequate hermetic seal."

Farm Girl said...

It all looks so good Meg, I am so glad you like canning.
I was thinking it will be time to make some strawberry soon.
We got the whole garden planted today, finally!

no spring chicken said...

I haven't made friends with a pressure canner yet but I'm willing if one presents herself!

Blessings, Debbie

Sue said...

Great advise Meg,I have been canning for years and am looking forward to my new season of preserving. Thank you for sharing your experiences in growing, and preserving your own foods.
Wishing you a most blessed Mother's Day.

Allison said...

What does that look mathematical to me? I'm backing up while reading this...telling myself to hold steady... SURELY I can do this! :)

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