If temperature is used to kill the baddies, then why the different "safe" temperature requirements?

Pasturizing fluids to use immediately 160 degrees or so.
Boiling fluids / water bath canning 212 degrees or so.
Pressure canning high acid foods 240 degrees or so.
Low acid veggie canning - commercial 250 degrees or so.

Should cooking thermometers be part of our BOB or Bug-in kits?

I suspect the lower temperatures represent situations, near term use and foods that are more susceptible to harboring food poisoning. Lower temperatures often 'deactivate' microbes, beat them around the head and shoulders and lower their populations to safe levels. This is okay short term but, inevitably, some of the bacteria will still be active. If the food is consumed quickly this small number isn't a problem. Whereas, if the food is a type that promotes easy growth and the food is not consumed in the short term those stunned bacteria start to multiply.

It's really a combination of time and temperature that does the work. For instance, you can pasteurize at 130 F, it just takes a several hours. Most pathogens don't grow well outside of their preferred PH range, which is why pickling works. Salt will desiccate their cell walls, too.

The reasons canning is done at a higher temp is that the food is being sterilized, not merely pasteurized. Pasteurization will result in as much as a 7D reduction in the amount of pathogens but since some of the most deadly thrive in anerobic conditions (eg a sealed can), given enough time even a very small amount of bacteria would be able to multiply to dangerous levels. This is why pasteurized milk won't keep forever, and why meats prepared sous vide are generally only considered safe to store under refrigeration for a few weeks. Heating to around 240 degrees for a few minutes kills "virtually" everything in the can. And of course, since water won't get hotter than roughly 212 F at atmospheric pressure you must use a pressure cooker to raise the temps to that level. Commercial canneries actually use equipment that agitates the cans as well, reducing the amount of time it takes to heat all the contents evenly.

Once food has been vacuumed and subjected to the heat of pressure canning it's shelf stable. While quality will eventually suffer food that's been properly canned can be safe to eat for over 70 years. MREs are another type of can; the retort pouches used to store them are actually called "flexible cans."

It's just different requirements for different conditions.

Pasturization doesn't sterile things, it just slows the growth of microbes. Milk and fruit juices, for instance, don't boil well.

Water bath canning is used for foods with either sugar (jelly, fruit in sugar syrup), or a high acid content (regular tomatoes, pickles); it's the two forces working together that get the job done at lower temps.

Pressure canning is to kill everything possible, used for foods that are low in sugar or acids (vegetables, meats).


You've got these a little mixed up:


Water-bath canning of high-acid foods needs temps between 212ºF and 250ºF -- the higher the temp, the shorter the time needed to get the job done.

Pressure canning of low-acid foods needs temps of 240ºF to 250ºF.



Unless you're planning on doing some serious milk pasturization, I would say No. If you can't recognize boiling by now, a thermometer probably won't help. And the temps that are listed are INTERNAL temperatures, anyway -- you can' reach them with a thermometer. The foods have to reach those temps for killing or inactivation of the pathogens.

Get going with your canning this summer, and after a few batches, you'll feel a lot more comfortable with it if you need it later.

Sue

Okay, thanks to all.

Now, why do I have to buy both a water bath canner and a pressure canner? Isn't there a decent multi-tasker out there?

And while we are at it, why can't there be an electric, self-heating unit, preferable with digital controls, that can be used without a burner - like in the galley of an under-equipped small sailboat?

You can use a pressure canner for water-bath canning, just don't put the lid on. See here for a chart on boiling times for water-bath canning, and you'll notice that the boiling time differs with size of container and density of contents.



The closest I have found is a Hot Pot which I discovered just a few months ago at a friend's house (she loves it). There is also the hot pot for liquids but they're more for just heating hot water to add to something. I've tried cooking things like soups in it directly, and it leaves a lot to be desired (very messy and some ingredients seem to react with the bottom heating unit). My Rival has lasted far longer than the others, but the design is very poor -- it dribbles all over when I pour.

What *I* would like to see are decent room lamps without cords.

Sue