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Tim F 10-15-2008 05:48 AM

Preserving jars in a WFO
Has anyone ever tried sterilising jars of fruit and veg etc in their WFO? It occurred to me today that you could stew or bake things while the oven is hot, put the lids on, then leave the jars in when it gets down to 120C or so.

egalecki 10-15-2008 06:50 AM

Re: Preserving jars in a WFO
I do a fair amount of canning of jams, salsa, beans, tomatoes, etc. I use a big pressure canner to do it. (I don't have to sterilize the jars if I process in a pressure canner)

I don't think it would be safe in the wfo for anything not high in acid or sugar- which can be canned in a boiling water bath. If you're doing low acid foods (green beans, etc) you really need to do it in a pressure canner, which raises the boiling point to a level which will kill clostridium botulinum- 240 deg. F.

I also think you'd end up with less than predictable times for canning- the wfo isn't temperature regulated.

I can see drying fruits and veg inside your wfo and then storing them, though.

Botulism is pretty darn unpleasant, so I don't think I'd risk it. I'm all for using the retained heat, but I don't think this is a good choice.

brokencookie 10-15-2008 05:41 PM

Re: Preserving jars in a WFO
I own and run a small premium jam business. I make jams, jellies, fruit butters and sauces. Over the last 12 years I have educated the local health department and many other canner about safety.
There are two different types of canning. High and low acid. Low acid Pressure canning is used for meat and veggies and anything with a pH of greater than 4.5. Temperature and pressure are related. By increasing the pressure you effectively get a rise in temp. As previously stated, you cannot kill the active molds and bateria until about 240 degrees. If you get your food up to that temp for the required amount of time you would not want to eat it. So pressure canning is a safe way to do this and still have edible food.
I specialize in high acid foods. High acid foods are foods with a pH of less than 4.5. Some of these foods have this pH naturally, some canners use additional acid ( like a lemon juice) to lower the pH to a safe level. The jars are then placed in a water bath for three reasons.

1. Water boils at a constant temperature making it easy to maintain for the required amount of time
2. Getting the product up to 210 F (100 C) expands the material in the jar, forcing out the air. As the product cools it pulls down the lid and forms a vacuum seal ( when rapidly cooled ). This is why canners leave 1/4 inch head space when they fill their jars.
3. Water bathing kills the active bateria (see more below), but does not kill the spores.

The final part of safe preserving is sugar content. This is not because of sweetness. Sugar is a preservative that inhibits baterial growth. However, you must have the combination of a less than 4.5 pH with a minimun of a 45 brix (% sugar) for this to work. If your sugar content is not high enough you have to use a preservative like sodium benzoate or potassium sorbate to keep the spores from growing. The most common is potassium sorbate( also used in wine making).

Sorry about the rant. I just spent 3 hours convincing a new health agent that a 100 year old process is safe. The tried and true methods work very well and, despite the simplicity, represent some fairly intense science. Canning in your WFO is more trouble than it's work and could potentially be dangerous.

Frances 10-16-2008 12:52 AM

Re: Preserving jars in a WFO
Cool, I knew the how of jam making but not the why. Learn something new each day, thanks cookie.

Tim F 10-16-2008 05:12 AM

Re: Preserving jars in a WFO
Good advice, thanks!

Mapleone 10-16-2008 11:17 AM

Re: Preserving jars in a WFO
It is so easy to use a pot and boiling water, it seems like it would not be worth the risk of trying to use a WFO.

Guerito 10-22-2008 01:04 PM

Re: Preserving jars in a WFO
brokencookie…Great explanation.

The pH scale is somewhat counter intuitive. High acid is at 0, and low acid (base) is at 14. As an old food processor, I can only reinforce what BC said. Botulism is more than a pain, it is a killer. You can’t see it or taste it. Just say good bye! :(


jengineer 10-22-2008 03:05 PM

Re: Preserving jars in a WFO
"Sorry about the rant. I just spent 3 hours convincing a new health agent that a 100 year old process is safe."

Wow if that was a rant I would like to see when you really get going.

Thanks for the primer. Good info especially when you talk chemistry

I don't totally agree with the Botulism comments though as being bad. When we visited Italy and Sicily I got a real good case of food poisioning. I puked on Naples and Dad Puked on Pompeii. We were staying in Rome at the time and were on our way out of town to a small village on the eastern side of the country. We decided not to tell mom. if we did it would have been more time in Rome and I was stuffed with too muchinformation of my past. You know it is bad when you can't hold down water. Suffice it to say that mom figured out something was wrong when she noticed neither dad nor I ate for 3 days. She called an army surgeon in Germany for advice - get fluids and electolytes in us. A doctor that visits the town once a week was going to take some blood as it was feared my kidneys and liver were starting to shut down. I said no worries if you don't take anything in nothing comes out - duh. Well I got worried when the urine came out BLACK and syruppy. However when the Doctor pulled out a needle and started cleaning it I siad no thanks I would rather die. Bottom line after a month in Italy I came back 5 pounds lighter!

Bugs kill and so do reused needles!

brokencookie 10-22-2008 05:12 PM

Re: Preserving jars in a WFO
Because we are so educated regarding food safety in my house we have a saying

"When in doubt, throw it out"

It is cheaper to throw out questionable food than to throw money at the hospital.

As cheap as I am, I never hesitate to throw out food that is even remotely off. Just think of it as an opportunity to go out and buy better food :D

jengineer 10-23-2008 08:25 AM

Re: Preserving jars in a WFO
Agreed - about 3 years ago I fianlly got a compost pile going. The wife is now more prone to feed the worms instead of wiaitng until a science experiment gets going.

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