canning without boiling - possible, but possibly deadly!

I'm going to use my moderator powers to bring this post to the front of this thread. Please heed this information well!

Eric Thompson wrote:Food safety is the main concern for any procedure and recipe for home canning. Any meat or vegetables that could have botulism should be pressure canned with a USDA approved recipe -- no matter how much someone insists how "Granny did it", botulism is deadly and not worth the risk.

My wife recently learned a method of canning in the oven that does not involve boiling cans in water and hence is less labor intensive.
Wanted to expose it to the community and take your input.

• Wash jars and heat them at 215°F (102°C, just above water boiling temperature) for 15 minutes.
  
• In the mean time, boil the lids in a pot.
  
• Remove the jars, put them on a blanket (lest the bottom cools and breaks)
  
• Fill with the product being preserved (which is boiling hot) and close the lids
  
• Put filed jars back in the oven and heat them at 315°F (157°C) for 10 minutes.
  
• Remove the jars, put them on a blanket and cover with a blanked so they cool very gradually for 24 hours.
  

This method requires decent quality glass. Ball and Kerr 32 ounce jars seem to work, except one we placed too close to heating element.
Also successfully tried French 1.5L Le Parfait and Italian Amici and Bormioli in various sizes.

More pictures to follow in the next post.

More pictures:

• Fill with the product being preserved (which is boiling hot) and close the lids
  
• Put filed jars back in the oven and heat them at 315°F (157°C) for 10 minutes.
  

More pictures:

• Remove the jars, put them on a blanket and cover with a blanked so they cool very gradually for 24 hours.
  

Looks like "water bath canning" without the bath. Water bath canning shortens the procedure, and I'm unsure of the energy trade off between boiling on a single element on the stove top and using the oven, although I suspect it leans more towards the single element. Be interesting thing to check with a watt use meter, although you could probably do a comparison of kwH used for bath canning and this process.

One caveat with water bath canning is it is fine for most fruit/vegetable canning, but many processes do require pressure canning to ensure food safety.

Food safety is the main concern for any procedure and recipe for home canning. Any meat or vegetables that could have botulism should be pressure canned with a USDA approved recipe -- no matter how much someone insists how "Granny did it", botulism is deadly and not worth the risk.

Some resources to keep it safe:
http://www.foodsafety.gov/blog/home_canning.html
Your local ag extension office

That link is excellent, and has a link in it to the pdf of the USDA's "Complete Guide to Home Canning".

http://nchfp.uga.edu/publications/usda/INTRO%20section%20Home%20Can.pdf

Low acid vegetables, meats and the like all need pressure canning to ensure you don't sicken and/or die from botulism. There isn't a "sniff test" for botulism.

I'm all for traditional food preservation methods like lax-fermentation, but not for attempting to defy death in the kitchen. The National Center for Home Food Preserving and the USDA advise STRONGLY against oven canning. I wouldn't eat that food, myself. If it's been less than 24 hours, you may be able to reprocess it properly. Otherwise, throw it out NOW!

Here's the CDC's overview on food-borne botulism: causes, symptoms, prevalence, etc. Don't risk it, it's not worth saving a joule or two.

I can't recommend this method for "canning." Yes, it's a bit less work but no, you're not transmitting the heat effectively to the product in the jar. Air is insulative and it just doesn't transmit heat like water does. The sauce in your pictures looks like it's got vegetables in it and unless you've added a fair amount of vinegar or lemon juice, I doubt the pH is below the 4.6 needed to ensure no botulism.

About 40 people a year get botulism in Italy, most from home canned vegetables. (204 over a 5 yr period, 1994-1998.) It's a thing. You can't smell it or see it. It's the only scary thing possible with home food preservation. If you are making acidic things and you mess up, you might get ugly molds, same with fermented foods. Nobody has ever died from eating home fermented foods. The same can not be said for botulism and low acid foods.

Even if you don't die you will most likely end up on a ventilator. I had a patient with infant botulism as a resident, she didn't need a ventilator, but she couldn't move her arms or legs or face for weeks, until she grew new nerve endings. The toxin binds irreversibly to your neuromuscular junctions, there is no antidote. We fed her with a tube going from her nose to her stomach and every 15 minutes the nurses came and sucked out her mouth, because she was at risk for choking on her own saliva.

I agree with everything Julia said above. The hot water conveys heat into the jar much more efficiently than hot air would. In an oven you never know if it might be much too hot and make a jar explode, whereas boiling water can't get any hotter than boiling point at your altitude unless it's under pressure, so you're protected from the jars getting too hot.

Boiling water bath canning doesn't need to be much more complicated than this oven process. Instead of special bottle-holding tongs, just wear either thick insulated rubber gloves (available in many hardware or grocery stores), or lacking that, thin winter gloves inside of thin rubber gloves. Then you can easily place the jars in the boiling water and take them out, adjust their position, and everything nice and careful.

Thanks for massive amount of feedback. That's was the reason I asked.
The recipes we use involve fair amount of vinegar.
Is "canning" an improper term then for what we do? Should I say have said "pickling" instead?

We have always preserved using water bath before, the only new step was using oven in lieu of water bath.
Colloquial grandmother wouldn't do it because her jars would explode.

Am I still missing something?

Speaking of botulism, wouldn't the excessive pressure build up and serve as a warning sign?

[quote=Seva Tokarev]Am I still missing something?[/quote]

When canning in an oven, you don't know what the conditions really are inside the jars... Ovens heat unevenly... Blankets vary in thickness...

Botulism doesn't create gasses in a jar when it grows...

In my most recent batch of canned pears, one of the jars broke during processing. Much better to have that happen in a pot of water than in an oven.

[quote=Joseph Lofthouse]
Botulism doesn't create gasses in a jar when it grows...
[/quote]

Now, that contradicts everything I knew. Could you please specify the source?

If other types of bacteria are growing in a jar with botulism, then those other species may produce gasses. The lack of gas creation by botulism is part of the reason why it is so deadly... People don't see/taste it lurking in the jar.

[quote=Joseph Lofthouse]If other types of bacteria are growing in a jar with botulism, then those other species may produce gasses. The lack of gas creation by botulism is part of the reason why it is so deadly... People don't see/taste it lurking in the jar. [/quote]

I was pretty sure that Clostridium botulinum [i]does[/i] produce notntrivial amount excess gases during its metabolism. Your saying contrary to that made me do research, and here is what I found:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC242325/pdf/aem00171-0229.pdf

According to that article, it depends on pH and glucose concentration. If glucose concentration is low or pH level is marginal (if it's lower than 4.6, C. botulinum does not grow at all,) toxin is produced but gas production is not.

According to my calculations, mere tablespoon of 5% vinegar per quart brings pH down to 4.2, and USDA guidelines call for much more vinegar than that.

[quote]In summary, this paper demonstrates that gas production is an unreliable indicator of growth and toxin production by C. botulinum[/quote]

There is a bit of good news I never knew before: according to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC546888/, botulinum toxin is quickly inactivated by heating (1 minute at 160°F.)

[quote=Seva Tokarev]
Speaking of botulism, wouldn't the excessive pressure build up and serve as a warning sign?[/quote]

NO!!! you can't count on warning signs. Gas may build up, but the myth of the bulging can is the sort of thing that gets people killed every year. From the DHHS (http://www.foodsafety.gov/blog/home_canning.html) Foodsafety.gov:

[quote=Foodsafety.gov]Clostridium botulinum grows well and can produce toxin inside closed jars of low-acid foods at room temperature, and you can’t always tell by looking. Jars of improperly canned vegetables and meats can contain the deadly botulism toxin without showing signs of spoilage. You can’t taste it or smell it, so you don’t even know it’s there, and it can kill you. The bacteria must be killed during the canning process for safe storage.[/quote]

Why oven canning is a bad idea.

The safety of long term storage of food in jars is a function of the sterility of the food and the integrity of the seal. The modern mason jar and lid works to pull a vacuum as the jar is heated (sometimes under pressure). The heat sterilizes the food, the vacuum creates the seal. It takes relatively little heat to create the vacuum*, far more for the food at the center of the jar to reach a temperature guaranteeing sterility.

The required temperature for sterility depends on the nature of the food: acidity or pH is the one we think about most, but also the density of the food. Juices take less time to heat than chunks of food in a syrup or sauce. The size of the jar is another variable. So the jar full of food has to be heated to a known, pathogen-killing temperature, and is sealed in the process. Why do it in water, instead of the oven?

1) oven temperatures are notoriously inconsistent. Unless your oven has been professionally calibrated (and the cheap thermometer from the home goods store that hangs on the rack isn't reliable either), you have no idea what temperature your oven is putting out.** Water boils at the same temperature (at a given altitude) everywhere on earth. Boiling water is the standard way to calibrate a thermometer. Safe recipes can be calibrated to use this known temperature. You can trust your life to the laws of physics of boiling water.

2) heat transfer in boiling water is faster and more uniform than in an oven. Ovens have cool and hot zones. Cookies on a sheet don't always cook the same from one side to the other. And some recipes you even need to move the cookie sheet from the upper to lower rack in the middle of the baking to compensate for the inconsistency. That's why they invented convection ovens, to attempt to even out the heating within the box. Boiling water is the same temperature everywhere.

3) More importantly, heat transfers much faster in water than air. Think about it. You can stick a bare arm in a 500 degree oven to retrieve your pizza, but you can't use your hands to scoop pasta out of boiling water without getting burnt. Water transfer heat much faster than air. Think about how long it takes for a cake to bake all the way through to the middle-somewhere around 30-45 minutes. Or a quiche, which takes as long or longer. Eggs will set at temperatures as low as 144. So if it takes a quiche 45 minutes for the center to set, how long is it going to take food in the center of a jar to hit a safe temperature?

4) We need a correction factor for altitude. I live at almost 7000'. Water boils here at 199.5, not 212. I have to add significant time to published canning recipes to account for the longer time it takes the center of the jar to reach a safe temperature. When I can under pressure (because low acid foods need a higher temperature to ensure safety than the maximum 212 reachable in a boiling water bath, I have to add more pressure. One of the scarier things about these oven canning recipes going around is that no one even mentions altitude.

One of our members, Erica Strauss, has a great infographic on how not to die from home canning.
http://www.nwedible.com/how-not-to-die-from-botulism-what-home-canners-need-to-know-about-the-worlds-most-deadly-toxin/

Her post also has a link to a Seattle news story about a guy who nearly died from home canned elk meat.
http://www.kplu.org/post/home-canning-hobby-leads-near-fatal-medical-emergency

Oven canning is one of the easier ways to earn a Darwin Award, and harm or kill the people you care about in the process. Just don't.

*I reuse canning jar lids for short term storage of leftovers in the refrigerator. Often just the cooling of the hot leftovers will pull a vacuum. That doesn't make it shelf-stable!
**Half of people's baking woes are from miscalibrated ovens. More ovens are wrong than right. Why someone doesn't offer a calibration service is a mystery to me. I still wouldn't can in an oven, but it would be nice to get my cookies to come out right.

[quote=Seva Tokarev]

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC242325/pdf/aem00171-0229.pdf

According to that article, it depends on pH and glucose concentration. If glucose concentration is low or pH level is marginal (if it's lower than 4.6, C. botulinum does not grow at all,) toxin is produced but gas production is not.

According to my calculations, mere tablespoon of 5% vinegar per quart brings pH down to 4.2, and USDA guidelines call for much more vinegar than that.

[/quote]

This is an example of dangerous or incomplete thinking or communication. The mere tablespoon of 5% vinegar per quart does not address the starting pH. It does not account for what ever liquid or alkaline substances exist inside the chunks that float in the liquid. Further, it is not just glucose, it is the concentration of sugars and or salts that affects the osmolarity of the solution. What's needed is a high enough concentration to create an osmotic pressure that prevents the growth of micro organisms. What's that concentration? I don't know, but it has to include the liquid that is incorporated in all the cells of the plant or animal material in the solution.

Here is how cautious I am: when I made tomatillo salsa for the first time, I had research from U of New Mexico, Las Cruces that said tomatillos were ~3.5 pH. But I was adding onions and chilis, both higher pH, and fresh garlic. The garlic, coming out of the ground is likely to bring the clostridium spores with it (they are ubiquitous in the soil). And it only takes ONE to kill me!

I don't want to die. I DON'T WANT TO DIE! And I don't know these people from Las Cruces, maybe they aren't very smart.... And being an expert carries NO special status with me. Experts are wrong every day, so I adjusted the pH down to 3 using pH paper. And water bathed it an hour.

I think people should be VERY cautious in all high risk activities, which means we need to understand what all the variables are in any given situation.

Sometimes I throw out a quart of chicken broth (pressure canned) just because I thought of the risk of botulism in chicken broth, and am superstitious enough to suspect that if I thought of it, it might be the one bad jar.

As for boiling for one minute, or it was quoted one minute at 160 F, I grew up with people boiling high risk food such as canned green beans for 20 minutes, at sea level. I would not risk my life on 160 F for one minute. When I am having company and I make chicken soup with the home canned broth, I boil that for 20 minutes. And then it crosses my mind that boiling at 5000 feet is not the same temperature as boiling at sea level, where I grew up, and all those people were boiling those green beans...

You just can't be too careful with food preservation. We lost a lot when there was a break in the generations passing the knowledge down, and now that there are young people wanting to learn to preserve their own food, where are they to go to get reliable information?

The links here are a good starting place, but as I said, I am careful even with the advice of the certified experts in the field.

Thekla

I'm going to lock this thread now.

I'm leaving it up in case it serves as a warning to anyone else who is thinking of trying this technique, but I think all the concerns have been addressed, and I want the take-home message to be

'don't try this at home'.