" Canning applies some serious heat for a fair amount of time, often over an hour. "

Can you give an example of something that requires such long processing? Most apple products I can think of only require 15-20 mins. Apples are very acidic so any processing time longer than 10 mins is either due to density issues or the other ingredients, not the pH of the apples.

As for the 5 min processing, keep in mind that is only if you use pre-sterilized jars. Otherwise even jams and preserves require 10 mins. 10 min is the norm.

Dave

Dave I wasn't referring to canning fruit, just other stuff we can.

In that case, yes, it is because the fruits - most of them - are so acidic to begin with. There are a few exceptions however, even with fruits.

Dave

Perhaps you read 'Applies' as 'apples' digdirt? ;-)

Traditional jam, ie half and half sugar and fruit, doesn't get canned at all in my part of the world.

Good point floral! ;-)

Dave

Floral_uk, do jams not get canned even if you are doing a large quantity which will not get used up for months?

Probably others here remember, as I do, a parent or grandparent making jams or jellies that were just covered with a layer of wax. I have a preserving book from the UK that shows pictures of jars just covered with static cling plastic wrap, it appears. I will occasionally make an odd lone jar of jam and not can it, but intend it for more or less immediate use. These days I will put that lone jar into the refrigerator, because we don't eat jam as quickly as we used to.

matthias, Grandma often used paraffin to seal her jars of jam. In fact, I have some old jam jars that don't even have threaded lids, they just have a metal lid that sits on top of the jar. I use one by the stove as a salt pig.

Anyway, her jam and jelly lasted for long periods in storage, but it was a messy and cumbersome procedure. She had an old coffee pot that she used to melt the paraffin. Pour a thin layer, pop the bubbles with a needle, pour some more. Make sure it's all the way to the edges so you get a good seal. Let it set and store, then try to clean up the mess. Ugh. I even caught a pan of paraffin on fire once.

So, it's as much a quality issue as it is a safety issue. Grandma learned to use rings and flats and never looked back at paraffin because she had more spoilage with that than she did with lids. paraffin is still used in pretty much every other country than here and some here still use it so they can put their fancy jam in pretty glasses for gifts. Here's what NCHFP has to say about it:

"USDA and the Cooperative Extension are endorsing a boiling water
canning process for jams and jellies which will make the potential for mold spoilage as small as possible. The cost of ingredients is high enough to make any preventable loss unacceptable. Paraffin or wax sealing of jars is no longer considered an equally acceptable choice for any sweet spread, including jellies. Any pinholes, shrinkage or cracks in the wax paraffin allow airborne molds to contaminate and grow on the product. In addition, leaks or holes in the paraffin can allow product to seep out during storage. Once on the surface, this seeping product will provide nutrients for molds to grow on the surface and enter into the jam or jelly in the jar."

So, as Grandma knew, you have less spoilage with a more consistently successful process.

Annie

Nope, Matthias, we don’t can jam at all. But we also tend to make full sugar recipes and not the unorthodox types like low sugar or weird ingredients of the kind I read about here. Chocolate in jam? Good grief.

We used to use paraffin wax. Nowadays we use wax paper discs on the surface and plastic jam pot covers held with an elastic band. Like this. Personally I use a plastic cover and then a screw top. I find that prevents shrinkage. Since we don’t can the jars we can use any sound jar. All mine are recycled ad infinitum.

eta obviously commercially produced jam is canned.