Pressure Canning

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JonB
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Post by JonB »

adam2 wrote:I would agree that caution and great care is required in home canning, which despite the name uses glass jars and not metalic cans.

In a previous thread on this subject, I advised caution, though not as forcefully as jonb.

As pointed out, the real risk is botulism which can be fatal.
Whilst only a fool would consume food that looked, smelled, or tasted spoiled, remember that food spoiled by botulism often seems fine.
Food affected by botulism is still dangerous to eat, no matter how thouroughly cooked.
(very thourough cooking kills the botulism spores, BUT the toxins produced by the spores remain, and can kill if eaten)

Pressure canning is less risky than water bath canning because the higher temperature is more likely to kill disease causing organisms.
Still NOT risk free though.

Canning of fruits and vegetables is considered less risky than meat, still NOT risk free though.

My personal preferenc is for freezing, useing at least two ultra high efficiency freezers and an off grid power source.
Deaths in the USA from home canned food have declined in recent decades, allegedly because the REA made electric power for refrigeration affordable and reduced the need for canning.
I'd agree entirely.
There are other methods that do not carry the risk, so would be safe (from a bot. point of view).
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Post by JonB »

Keela wrote:Hmmmmm....

I did lots of pressure canning the first year with my All American canner. However to do meats (which I did) I found the time taken to pressure can it was huge. 1 & half hours at pressure for only 5 litres of meat. I carefully followed the instructions in the book and have always boiled the resulting stew for 10mins after opening. It just seems to take such a long time to do though! The freezer is much more useful! On the other hand it is very easy to open a jar of stew/soup and boil it up... defrosting is slow!

I still bottle tomato sauce in the autumn and usually just water bath it. If I add other things then I follow a recipe from the Ball book, or the US Gov one, and pressure can as instructed - but truth be told I haven't used the canner for months!

Thanks for the warnings Jon.
You sound like you have looked into it and followed the US guidance.

The issue in process time is the temperature reached of the mid point of any particle or material at the coolest point of the pressure vessel in the process. If you do not know this, then the process is unsafe. The manufacturer will produce data for their machines when they leave the factory against an ideal recipe. Problems can occur with seal partial failure, valve seats, pressure gauges (and their accuracy / calibration), the list is long.

Please be very careful.
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Post by JonB »

Keela wrote:
JonB wrote:I am extremely concerned by this thread.........
........If you must do this, I strongly suggest that you gain a strong, technical understanding of the process and its risks. This doesn't mean just buying a couple of books...............
Recommended reading?
Sorry, I wouldn't like to on this.
If I have any issues at work, I would consult a bot. expert (I'm not one)
I would consult an industry canning course as a good start.

This is a good book on botulinum.

http://www.DODGY TAX AVOIDERS.co.uk/Clostridium-Bot ... 390&sr=8-1

I know of both authors. Both are brilliant microbiologists who are senior industry figures, and the books are widely used in the food industry.
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Post by JonB »

Keela wrote:Hmmmm.... my comment above suggests that the spores breed which is not what I meant to imply .... of course it is the bacteria themselves that breed and not their resistant spores.....

So the bacteria can be killed by boiling - but their spores which are more resistant to heat cannot.

Live bacteria are dangerous.... but what about the spores they produce? Can the spores hatch in the human gut and become a danger?


Yes in babies. Causes infant botulism. Nasty.
For others, the problem is the spore surviving your process, then germinating in the container, growing and producing toxin.
To give you an idea, the recommended process is the mid point of any particle at the coolest part of the process is 121 C for 3 minutes.

What I'm asking is - if any potential toxins are destroyed by boiling after opening a jar, and the bacteria themselves are killed in the boiling.... can the spores that might have survived in an improperly canned jar do damage themselves??? (Afterall they will not be affected by the cooking after opening of the jar; as boiling is 100'C & not the higher temp needed to destroy spores..... )

Jon? 8)

I was led to believe that boiling for ten minutes before eating was a good "to be sure, to be sure" method of ensuring canned food was safe (along with the obvious proviso that it both looks and smells right and still has an intact seal). Am I wrong?
The toxin is destroyed by heat. However, in a canned product failure a huge amount of toxin is produced and as bot toxin is the most toxic substance by weight known to man, I would not bet my life on it.
I would strongly suggest you learn a lot more about botulinum.
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Post by JonB »

kenneal wrote:As I remember from biology lessons at school 45 years ago bacteria form spores as a protection measure against sudden changes in their local environment. If the changes are sufficiently quick they don't have time to change into spores and can be killed off completely. So it is important to change temperatures quickly, fast boiling and quick freezing, fast boiling and then quickly cooling when blanching, to preserve food properly.

Is that right Jon?
In theory, yes.
In practice, you cannot achieve that reliably in the home environment.
It also ignores the high probability that some spores already exist in the food matrix and will be unaffected.

Botulinum is an obligate anaerobe, which means it will only grow without oxygen. Therefore the normal environment encourages spore formation.
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Post by JonB »

Sorry for the large number of posts.
I thought it best to respond to each person individually.
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biffvernon
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Post by biffvernon »

Here are the data:
http://www.hpa.org.uk/Topics/Infectious ... gicalData/

Wound deaths (associated with drug injection) kills about one person per year in the UK. Food related: three deaths in 26 years.

Maybe we need to see things in perspective.

According to this page there are about 500 fatal cases out of a total of 850000 cases of food poisoning per year. Botulism doesn't seem to be too great a contribution to those numbers.
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Post by kenneal - lagger »

JonB wrote:Sorry for the large number of posts.
I thought it best to respond to each person individually.
Don't apologise, Jon. Thanks for your time and expertise.

Biff, could the low numbers reflect the small amount of home bottling currently undertaken in this country? In generations past the amount of home preserving would have been much higher and, possibly, the number of incidents and deaths.
Biffvernon wrote:Maybe we need to see things in perspective.
I would agree with that statement as well. Nothing annoys me more than the adverts on TV claiming that this or that product kills 99% of all known germs. 99% of all known germs are harmless and it's the 1% of particularly virulent germs which these products probably leave behind that cause the trouble. Killing off the competition leaves a clear playing field for the virulent germs, giving them a better chance.

Also if children grow up in a relatively germ free environment they don't have the immunity for when they come up against an infection. I am sure we have a greater death rate now than when we didn't use all these superproducts to disinfect our living environment. In my childhood days you got a tummy ache or the runs but didn't die from it or end up in hospital. Nowadays the first thing you hear is that people have been taken to hospital and a few have died from an outbreak of food poisoning.

It's the same with all these supadupa toilet cleaners. The answer is simple, "Don't drink from your toilet", and, of course, wash your hands after using the loo.

Most of these disinfectant products are a waste of money and are designed to increase economic growth. They are thus unsustainable and should be banned.

Rant over. :shock: :shock: :shock:
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biffvernon
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Post by biffvernon »

Yes, Ken, one needs to look at mortality as a proportion of the at risk population - those who eat home-canned food. It still looks a vanishingly small number though.

That 99% germ thing is not quite as you put it, I gather.

There's a standardised test using just the two commonest food-spoiling bacteria. A standard concentration of the chemical being tested is applied to the bugs for a standard length of time at a standard temperature and it is judged OK if 99% of those bugs die. This then gets translated into utterly meaningless advertising copy which the Advertising Standards Authority accepts.
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Post by adam2 »

As others post, the risks would appear limited, but caution is still advised.

Home canning is very rare in the UK, which may also account for the low body count.

The apparent very low risk is no consolation if an error in home canning wipes out your family, perhaps in some years time when the produce is consumed.

There are many other methods of preserving foods, inluding drying, salting, pickling, smoking and freezing.
Whilst these methods also carry risks, spoilage is normally readily detected with the senses.
Improperly cured or smoked meat for example will normaly look or smell "off" and no sensible person would consume it.
Home canned food spoiled by botulism often smells, looks and tastes just fine.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
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Post by JonB »

biffvernon wrote:Here are the data:
http://www.hpa.org.uk/Topics/Infectious ... gicalData/

Wound deaths (associated with drug injection) kills about one person per year in the UK. Food related: three deaths in 26 years.

Maybe we need to see things in perspective.

According to this page there are about 500 fatal cases out of a total of 850000 cases of food poisoning per year. Botulism doesn't seem to be too great a contribution to those numbers.
That's right.
Down to a lot of hard work.
The problem is that bot. has a high death rate.
I know someone who was at the company with the hazelnut yoghurt
problem. I wouldn't wish that situation on my worst enemy.
It is something that is still talked about and poured over in the industry today.
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Post by JonB »

Forgot to say, 80% of all food poisoning and therefore deaths are due to hygiene failures in the home environment.
For some reason this is not a priority to HMG. The FSA does make an effort, but its wider than that.
As Kenneal pointed out, domestic science has been lost. With proper hygiene taught as part of this, it could save a lot of lives, as well as a lot of money.
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Post by Leaf »

Can't believe I tripped over this site today!

I recently bought an All-American 21.5qt canner from Overstock.com.
Cheaper than ebay and guaranteed no additional charges.i.e. customs.

I've also got the recommended book on Botulism on its way.

When it comes to jars Le Parfait told me their jars are okay up to 1bar pressure. They also do a podcast for various recipes "le parfait tv".

Anyone got any ideas on converting sterilising times and pressure from a pressure cooker to a pressure canner?
I think I read somewhere that times for a pressure cooker were 1/3 longer that a pressure canner. Why I do not know!
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adam2
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Post by adam2 »

Home canning useing glass jars can be very useful to save seasonal surpluses for example.
It is not that dangerous, most people survive, but I would urge careful study of the risks before proceeding.
Death from botulism is very rare in the UK, but that might be because home canning is very rare in the UK.
Deaths occur regularly in the USA were the process is more popular.
Especialy see the cautions by JonB, some posts back.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
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emordnilap
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Post by emordnilap »

Welcome, Leaf.
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