It might be. AFAIK, though, nobody knows as testing hasn't been done with that particular set of conditions.

There's a huge problem with oven variability and unreliability, as well as various "hot spots" and "less-hot spots" depending upon the oven. So one of the main issues is that it would be almost impossible to come up with a consistently safe time to accomodate every possibility out there.

On the other hand, boiling water is boiling water, so regardless of how long it takes a particular stove to come up to heat (even a wood stove), once at temperature processing results will be reliably safe for every appliance.

I might also add that 4 hours in an oven is can be incredibly energy-wasteful.

Carol

Agree. It is very wasteful of energy not to mention much less efficient. Manufacturers of canning jars do not recommend baking or oven canning in the jars. Does it result in safe food? Who knows. Do jars break? Yes, so disadvantages? Yes. Does it have any advantages over a BWB? Can't see how it could.

Dave

Oven Canning Oven-canning is extremely hazardous. The oven canning method involves placing jars in an oven and heating. In oven canning, product temperatures never exceed the boiling point, and uniform heat penetration cannot be assured. It is, therefore, not considered safe to use for home canning. Because this process fails to destroy the many bacteria, including the spores of Clostridium botulinum, it can cause the food to become toxic during storage. Also, canning jars are not designed for intense dry heat and may explode resulting in serious cuts or burns.

You have to have the water over the tops of the jars by 1 to 2 inches. Just part way up will not suffice.
How would you keep water boiling the entire time to process jars ? It take boiling water for a determined time for each food to kill the types of bacteria in the jars that would cause spoilage as well as get a true vacuum seal. Not having the water boiling the entire processing time would not allow for the food to be safe.
Processing on the stove top is much more effecient and faster.

a huge problem with oven variability and unreliability

I would have to say this would be my biggest concern. When we bought our home 23 years ago, it came with a stove and fridge. The first few times that I cooked in the oven, I couldn't figure out why things weren't getting done when they were supposed to. Some things cooked too fast, some too slow. Needless to say, the oven temperature "thingy" was out of whack. Good excuse to buy a new stove :-)

Val

I raised my own tomatoes, so I knew they were high acid. They could make chapped lips squeal. I open kettle/ oven canned them for 20 years without losing a jar, but I was extremely careful and clean. Also I knew my oven.
Oven canning of dry ingredients might or might not work, but it won't hurt you. Bacteria won't grow in noodles that won't grow bacteria in a box on the shelf. Flower might get bugs, but it probably won't. Oven sugar? Can't hurt you. If the jar seals, ants can't get in. I seal-a-meal sealed a 5 pound bag of flour, and forgot it in a drawer for ten years. I thought it would be bad, but no bugs, and I couldn't tell any difference in bread, pie crust, or gravy. I didn't tell, and my family didn't say a thing.

They could make chapped lips squeal. Doesn't necessarily mean they were high-acid. They could just have been low sugar.

Cleanliness is no guarantee either. Botulism can grow with clean product in a sterile jar.

But, if someone wants to can jams in the oven, cognisant of the possibility of jar breakage, that's their prerogative. So is sealing of dry goods, though I would think you could achieve the same results with lids prepped in hot water and hot jars. I doubt you'd even need to use an oven.

However, it's all personal choice. We try to point out benefits and risks. It's up to the individual to decide what to accept and what to reject.

Carol

I raised my own tomatoes, so I knew they were high acid.

Sorry but there is no such thing as a "high acid tomato". All varieties have been pH tested numerous times and charts are available for the results.

As Carol said, oven canning and open-kettle canning are your choice, risks and all. But neither proven to be unsafe approach is something to be advocated for others.

Dave

I met a woman at a farmers market this weekend who has a new small business and cans in an industrial kitchen. I asked her about her methods of canning because she creates all of her own recipes. I wanted to know how she knows her recipes are safe and whether she has had them tested. She told me not to worry and explained the oven canning process that she uses. Her products are in 1/4 pint ball jars. She makes tomato and fruit jams.

Do you know if oven canning is ok for food companies (maybe they have some special equipment)?
Is there a reason she can make up her own recipes and sell to the public? For example, is testing required?
Do you think it is safe to eat her jams? I brought a group of students to the market and some I them wanted to buy the jam.
Is there a way I can make up a recipe (fruit/tomato/pickle or low acid vegetable) and test it for safety?

Thanks so much for your thoughts on this!

I worked in a cannery as a college student and don't know of any commercial cannery that cans in ovens. Generally they use pressure canners and their methods are determined by the standards of the FDA.

The fact that someone uses an "industrial" kitchen is irrelevant. Using an oven is not recommended for canning for the reasons posted above, and a commercial oven would be no different.

Her jams are probably safe (not sure about the tomato jam depending upon the recipe) as most fruits are high acid and jams are also high sugar. So the product itself is for the most part low-risk regardless of the process.

It sounds as if your first step is to do a lot of reading and studying to bring you up to speed on the principles of canning and the safety issues before worrying about "making up a recipe." I'd recommend the NCHFP self-paced online course. It's free and a great way to begin.

As far as your seller is concerned, I wouldn't touch anything she sells aside from a high-acid fruit jam. Many farmer's markets are not adequately regulated and there is risk with some of the products sold.

Carol

Here is a link that might be useful: NCHFP Home Page

Do you suppose that she meant that she cooked the food in the oven to reduce the liquid, then canned it the traditional way and sealed it in a boiling water bath. Otherwise, that's just scary.

You don't say what state the farmer's market is in. Laws vary from state to state, but AFAIK, if you are a commercial food processor (and not a cottage industry, as some states allow farmers to process their own fruit into jams and jellies without testing), you must have documented procedures on file. I can't imagine that oven canning would be allowed - but then again, apparently the Blue Chair Jam company does it, since that is the method described in their/her cookbook (an alternate method is described as "according to the manufacturer's instructions" - we can only assume that means BWB as described on Ball's website).

As far as your seller is concerned, I wouldn't touch anything she sells aside from a high-acid fruit jam. Many farmer's markets are not adequately regulated and there is risk with some of the products sold.

Ditto what Carol said.

And the seller's "don't worry" and "making up her own recipes" comments would have inclined me to contact the local health department about her too. Most counties and states have at least some rules the seller has to abide by when selling to the public.

Do not make up your own recipes is the #1 rule of safe home canning.

Dave

I would like to make some of the jams in the Blue Chair Jam cookbook but I am wary of the oven thing also. I wonder how she sells those jams in big name stores in California. We have a lot of regulations. My question is how do you convert the oven times that a book like that recommends to water bath processing times without overprocessing and losing the fresh flavors. I've never processed anything high acid under ten minutes.
Mary

The standard time for any sweet preserve in 8-oz. jars is 10 minutes BWB. Sometimes I see a recipe which specifies a longer time but 10 minutes is perfectly adequate.

Carol

I am from Europe where oven canning is very popular and not considered "dangerous", so I am shocked that it is in the USA. Knowing a little physics and chemistry I find the arguments for not canning in the oven silly. I have been canning in the oven without any problems - just have everything hot and watch for bubbles in the jars. Here is a very good explanation written by science teacher on thriftyfun.com why canning in the oven CANNOT be unsafe (I hope that she doesn't mind me copying her comment as I found it very good and educational):

By ann.welch 1 09/30/2015: "Firstly, I can't possibly see why food in a glass jar which
is placed in an oven for long enough won't reach the desired temperature
throughout. If I thought that it wouldn't, I'd never eat a roast chicken ever
again !!! I'm a physics teacher and heat is transferred if there is a gradient
i.e. like water, it will "flow" either up or down with time and temp
difference. The bigger the temp difference the quicker it will flow. You need
to realize that we are talking about heat flowing through the liquid inside the
jar and not the air in the oven. Heat transfer through the air in the oven is
irrelevant as it is already at the desired temperature which is then maintained
by the elements.

Secondly, submerging the jar makes no difference to air
bubbles rising. They will rise in an oven just the same as a water bath because
they are contained within a jar. What's outside the jar (water or air) is again
irrelevant.

Thirdly, if the lid isn't sealed the jar is NOT going to
explode, trust me !! Why on earth would it. Glass is red hot when it's made in
the first place and would only break in an oven due to either high pressure
inside (if the lid were sealed) OR if the glass was thick and it was unevenly
heated very quickly (thermal shock) i.e. if the inside surface was much colder
than outside surface which would cause uneven expansion within the glass
itself.

I do understand that some people might not follow the
instructions properly and that Botulism etc. therefore could be an issue BUT
that's the same situation whether the jar of food is placed in a water bath or
an over.

Sorry to disagree with you all but if you are going to quote
physics please get it right."

Here's the thread referenced in the comment above mine. http://www.thriftyfun.com/tf19564724.tip.html

It doesn't feel right to pick apart someone's comment when that person isn't even present, so I won't do it. All the safety issues have already been stated anyway (both in this thread and in the one I've linked).

Rodney

Dear theforgottenone1013(MI zone 5b/6a) - I do not understand what you are talking about. My purpose was not to quote the whole link on the thriftyfun, but to quote one opinion from one person. I DID NOT pick apart any comment, so I do not know what you are talking about. I just omitted irrelevant first sentence ("I
know this thread is a little old but I thought it worth a comment anyway,
particularly as it still forms a reference to those looking for information"), but the rest is quoted exactly as it appears on the thriftyfun. You are obviously the opponent of oven canning and it is fine, but everyone can make their own decision - we only have to have facts to learn from, not myths.

More real life stories of oven canning: http://whatjuliaate.blogspot.com/2011/02/oven-canning.html

or By MarieJ1 08/02/2011 from the same thread on thriftyfun (starting with "I have canned in the oven for decades. I have never lost a jar of food by doing so…"); and I'm sure many more stories like that, but I do not have time to look for them for you. Or ask any person from Europe if oven canning is safe…

I think Rodney meant that there was no point in us picking apart (arguing with) the quote you posted since the individual quoted isn't here to defend themselves.

I'll add that their observations are nothing more than anecdotal info based only on personal experience and posted on a source which is not any sort of authority on the subject. The value of information is at least partially based on the value of the source of that information.

On the other hand lab testing by the USDA has shown that it is NOT safe to oven-process food because the temperature will vary according
to the accuracy of oven regulators and circulation of heat. Testing on jars that have been processed in that way show inconsistent internal temperatures, pockets where the temperature can vary by as much as 10 degrees F and such pockets do not appear in the foods when boiling water bath processing is used instead. This is because dry heat vs. wet heat is
very slow in penetrating into jars of food so much longer processing times would be required. Also, per the jar manufacturers, jars can indeed explode in the oven.

So when dealing with high acid foods or pickled foods in a brine that is at least 50% 5% vinegar those pockets of inconsistent temperature may pose no threat other than molds, fungi, and a shorter shelf life. But in low-acid foods or foods not properly acidified bacteria can survive easily. For that reason alone oven canning is not considered safe to do by the USDA and FDA.

The research available at NCHFP/USDA but still the choice is always yours whether to follow those guidelines or not.

Dave

Well, Dave, I think that physics laws are pretty good source of information. Of course how people apply them is a different story.

Think: the liquid in the jar, in the oven or not, will boil, to make it simple, in 212 degrees (boiling temperature of water). Is it right? So, even if you have heat fluctuations in the oven, the liquid in the jar will not boil until it reaches 212 degrees. Do you agree? So it might take a bit longer than in water bath, but it is equally safe or even safer, since one should heat oven to 250 degree. Anyway, it is safe in Europe, and I do not know what is the exact reason why it is not with NCHFP/USDA. The only thing I can think about would be that people wouldn't follow the safety procedures for oven canning and that would create a lot of lawsuits.

As for "individual quoted isn't here to defend themselves." - no one was attacking anyone, so there is no need for any defense! Are you and Rodney saying that I cannot quote anything because the person who wrote what I quote is not participating in the discussion? I clearly stated that I am quoting (and the quote is in the public domain), so every person knows that it is a quote, meaning the author is not necessarily participating in the discussion.

I am not going to participate in this thread anymore; I've looked at the oven canning material in the Internet only because I am translating the procedure for my american friend.

I hope that I haven't upset anyone with my posts, if I did - my apologies.

Are you and Rodney saying that I cannot quote anything because the
person who wrote what I quote is not participating in the discussion? I
clearly stated that I am quoting (and the quote is in the public
domain), so every person knows that it is a quote, meaning the author

No we aren't saying that. Just that it would be unfair to critique that person's comment without their participation.

Think: the liquid in the jar, in the oven or not, will boil, to make it
simple, in 212 degrees (boiling temperature of water). Is it right? So,
even if you have heat fluctuations in the oven, the liquid in the jar
will not boil until it reaches 212 degrees. Do you agree?

I agree in theory but the issue is the amount of time required for that to happen - reach boiling point - and then the time required to keep it at boiling point. No such times have been calculated with any research. And even if they had been, as explained early on in this discussion, those times could easily vary from oven to oven, vary based on the number and size of jars in the oven of one time, vary based on the amount of air circulation within the oven and among the jars, and vary based on the density of the jar contents.

Lastly is the point that there are little to no advantages to oven-canning over BWB canning. It requires a greater expenditure of energy and more time.

There are many food preserving practices in other countries that those of us trained in the USDA/FDA methods are aware of, methods that are strongly discouraged in the US because of research done on them. But ultimately the methodology used remains the individual's choice as each of us chooses the level of risk we are comfortable with.

Dave

"I think Rodney meant that there was no point in us picking apart (arguing with) the quote you posted since the individual quoted isn't here to defend themselves."

Yes, that's what I meant.

Rodney