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This article is from the Food Preserving FAQ, by Eric Decker ericnospam@getcomputing.com with numerous contributions by others. Can I use a device sold as a steam canner in food processing?

No. These devices which consist of a lidded pot used to be sold as a
"atmospheric canner". Putting Food By is strictly opposed to such devices -
they do not do the job. USDA and AgCanada are strong in thier denunciation of
said devices.

That being said, a great explanation in explaining why the device is useless
comes from Robert Matern who wrote:

"The physics is clear, and undeniable. The only way to make convection
work faster for cooking of any form is to speed it up (forced airflow),
a sort of reverse-windchill. This is why something like the Jetstream
Oven and similar devices work so much faster than traditional ovens,
toaster ovens, and regular convection ovens - high speed airflow, not
higher temperature. This would speed up heat transfer with steam, also,
but none of the non-pressurized steam canners I've seen use forced
airflow. The time differential between regular convection and a
Jet-Stream type oven is 3:1 to 4:1 or more. For a steam canner, you'd
probably have to quadruple the processing time over boiling water
canning in order to be safe; but without standardized testing, you still
wouldn't be SURE. Why risk it?"

Sandy from halcyon.com writes another great article"

I wonder what catalog you're reading. I've seen this in the Territorial
Seed catalog, from Oregon. I think they have great seeds for the Pacific
NW, but this claim they make is idiotic. I've tried to get them to
remove that text, but they've refused. I have not been able to make them
understand that on this planet, under normal atomospheric conditions,
steam is not hotter than boiling water.

Here's what I've written in the past on this question:

When you boil water, it gets hotter and hotter until it reaches 212
degrees Fahrenheit. At this point, no matter how long you continue to
boil, it stays the same temperature. The water evaporates and becomes
steam. This steam is also the same temperature, 212 degrees F. The
only way to make the steam hotter (and/or to boil the water at a higher
temperature) is to put the system under pressure. This is what a
pressure canner does. (As an aside, steam heat in an apartment
building is steam that is generated under pressure and is therefore
hotter than steam generated by a pot of unpressurized boiling water.)

You can put your hand in a 200-degree F oven and it will feel warm but
tolerable. If you put your hand in 200-degree F water (close to
boiling) you will get a severe burn. This is due to the different
methods of heat transfer: air is a poor conductor; water is a good
conductor. Think of being outside when it's 70 degrees F (quite
pleasant) versus being in a pool of water at 70 degrees (feels very

This transfer difference is what makes steam canners poorly suited to
canning: you need good heat transfer so that not only the outside of
the jars, but the contents at the centers of the jars get thoroughly
heated to 212 degrees F. (This is also why smaller, narrower jars are
preferred over larger, wider ones -- the heat does not reliably reach
and cook the food at the centers.) This will definitely happen in a
boiling-water bath when jars are processed for the prescribed times.
This will not reliably happen in a steam canner. IF you're canning a
high-acid food, such as fruit jam, AND it's been made with a HIGH ratio
of sugar, AND you've cooked everything properly AND sterilized the
jars, a steam canner might POSSIBLY be safe to use. However, there are
too many variables to be absolutely sure and I, for one, use the
methods that result in the lowest risk. I'm not sure why everyone
thinks steam canning is that much easier, either. There's a high risk
of getting burned from the steam when removing the unusually large
cover, and you're still boiling water (although a smaller amount) which
will still heat up your kitchen. A steam canner is just a large pot
with a high lid but inverted -- the lid goes on the bottom and gets
filled with water, and the former-pot-but-now-a-lid sits on top to trap
the steam. Why not just get a good, large pot that will be useful at
other times of the year, too?"


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