Monday, February 28, 2011

Oven Canning


NOTE: Oven canning is a controversial subject that I wanted to discuss, not necessarily to recommend. I want to state again that the NCHFP is against oven canning, and they make the guidelines for safe food preservation. If you are a new canner, please stick with a boiling water bath to process your food. Please read through all the comments, they are informative and helpful. I want to stress that when discussing this procedure, it is with regard to high-acid jams, marmalades and jellies only.

Recently I made some star fruit jam (recipe to follow in a few days!). It was a rather large batch, so I felt it was time to try something new: a method of sealing your jars that is called oven canning. There's a lot of dissent on the subject, and I'm writing down what I've come across, both yay and nay, in order to make some sense of the subject. I'd love to hear from you in the comments section if you have any thoughts!

I first became aware of this technique via artisan jam company, Blue Chair Fruit. BCF proprietor, jammer and author, Rachel Saunders, uses the oven for sealing her jars and recommends this process in her book. Many other small jamming companies use this procedure. Why? I think the biggest reason is because you can process a lot of jars at once. What's surprising is it's frowned upon by the National Center for Home Preserving, and many other canning heavy hitters. So then why are companies allowed to do it? [Side note: Honestly, you could let your jars seal on their own (which is called open kettle sealing) and no one would be the wiser. It's sealed, right? Who cares how you sealed it? And, as you won't get any really bad stuff from fruit (as long as said fruit are not low acid) you really would never know. Oops! I'm digressing.]

I've been asking around about this, ever since a friend of mine took a class with BCF and raved about the technique. She loved that she didn't need to bring her big pot out, and fill it with water, etc. etc. Point taken. Rebecca at RCakewalk also found it to be a great technique; check out her post on it. I pestered Doris from Doris and Jilly Cook about it and she said, sure, why not? As long as you don't get silly and use this technique with anything but fruit. Why? Because fruit is higher in acid, and generally less risky. (Please see Doris' comment below, with clarification on what she had said to me about oven canning.)

Here's how it goes:

Oven canning: Heat your oven to 250 degrees. If you are not sure of your oven's temperatures, and don't have a oven thermometer, I suggest that you stick with water bath canning. (And then, go out and buy a oven thermometer, for goodness sakes! They're, like, four bucks.) On a cookie tray arrange your jars facing up. You will want to heat these for a good thirty minutes. BCF recommends putting the lids in at the same time, but I thought that might compromise the rubber seal so I put them in, rubber side up, at the last ten minutes.

Be careful! If you leave the jars in over a half hour (which is fine) please watch out when you start ladling your fruit in. Always, always pour a little bit in first. If the jars are too hot, it will bubble immediately (and possibly splatter you). If this happens, let the jars cool a few minutes before you begin. Fill the jars as directed in your recipe (usually 1/4 to 1/2 inch). Seal the jars, and return them to the oven for about fifteen minutes. When they are done, put the cookie tray with the jars on it cool on a rack. They will ping as usual, and seal themselves.

It took me a while to try this out as I'm a creature of habit, and I've come to find that this technique seemingly works just fine. The best thing about it, is that when doing larger batches (which I rarely do) it's easier. It's also a lot quieter. Call me crazy but a pot of water boiling furiously for almost an hour sort of keeps me on edge. Using the oven, it was just me and the pot of jam. I usually do very small batches, only around four or five half-pints at a time.

However, I am new to this process and am still feeling it out. I would love hear what you have to say about it. Have you tried it? Do you love it? Do you utilize it in your business? When Saunders was on Martha Stewart's show, she made a jam and also showed her oven technique. Martha seemed to dig it. There's a lot of appreciation for it, but there's also a great deal of vehement opposition.

Here are a few quotes from some venerable institutions, all in the anti-oven-canning-camp:

From the National Center for Home Food Preservation:

"Is it safe to process food in the oven?
No. This can be dangerous because the temperature will vary according to the accuracty of oven regulators and circulation of heat. Dry heat is very slow in penetrating into jars of food. Also, jars explode easily in the oven."

From the Agricultural Extension Service at the University of Tennessee:

"...food inside a canning jar in the oven can be heated no higher than the boiling point of water (212 degress F at sea level) regardless of how high the air temperature is inside the oven. This is a basic law of physics."


From Pick Your Own:

"Oven canning is extremely hazardous."

59 comments:

  1. Well, as with all canning, it sounds likely to lead to burns - I learned one very important lesson in my high school chemistry class: (up to a very high point) Hot glass looks exactly the same as cold glass.

    Thanks for this clear write up.

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  2. Here are my problems with oven canning:

    1. In my oven at least, the temperature varies wildy from spot to spot. Edges, front, back, middle - they can vary up to 40 degrees. I do have an oven thermometer, but it would be hard for me to fill a tray with jars and have them all be at the same temperature.

    2. My oven is gas, which means it cycles on & off, on & off. It's difficult to keep it at a consistent temperature, especially over a short interval like 15 minutes.

    3. I can roast a chicken in a 375 degree oven for an hour and it will just reach 170 degrees. Granted, jam/preserves should aleady be close to boiling when you put it in the oven, but I'm not confident that 250 degree air temp is really keeping the contents of the jars at 212 for that period of time.

    4. As you say - for high acid fruits, you really just need to ensure a good, long-lasting seal (which is pretty much the only reason for water bath canning of fruit jams, IMO). Again, a good seal is provided by the strength of the vaccum which is provided by the contents boiling and forcing out air. Just not sure how well this will happen in an oven. And if I am not overly concerned about a great seal, just worried about botulism/acidity.. well, I would skip both the water bath and the oven process and just fill jars and allow them to seal.

    So - there you are. :)

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  3. I love the controversy! I am also aware of Rachel's method and would love to try it. I currently use water bath canning and pressure canning (pumpkin) for my business and it is very time consuming. I am always looking for ways to increase the business productivity. I appreciate your post :)

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  4. I like the concept of oven canning, but sheesh, I have no idea if it's a wise method. I hate when there are so many conflicting opinions to sift through. If it's a matter of taste, I love debate, but when it's a matter of safety, it's not so fun. Truthfully, if I had a canning question I'd just ask you and Shae for your opinions.

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  5. I'm with Denise- any canning questions I'd just ask you, Shae, Kaela or Kate.
    The concept seems worth trying for jams and high acid things!

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  6. Thanks for doing this post, Jules. I think it's important to dispel the idea that oven canning "is extremely hazardous" for high-acid fruit preserves that get poured piping hot into jars. Cuz it's just not. It's fine.

    That said, I know I'm not the friend who came back from Rachel's classes raving about the oven-canning method, because while I learned it there and have great respect for its ability to get a large number of jars processed quickly, my one attempt at it was not so good.

    I was going to say "not so hot," but it was very hot. I painfully burned myself more than once (which I almost never do while water bath canning) and for some reason I had a serious boil over problem, with the mixture in the jars bubbling up and spilling over while in the oven, even though I'd used the correct head space. It was a mess. Granted, I desperately need a new oven because the temp control on mine is terrible. I'm sure I'll try oven canning again after we get a new range, but I'm not in a rush.

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  7. I love that you posted about this alternate method of canning. My great grandmother used to can this way when canning large batches of jam, if she didn't just open kettle them, and she never had an explosion of jars. Now that I'm starting to can on a regular basis, my grandmother and mother are eager to find out if I'll use my great grandmother's techniques, and up until now I've been water bathing religiously thanks to fear instilled by the USDA. I think I might give this a try, maybe with one of my great grandmother's recipes, just to see if it turns out the same.

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  8. I took a marmalade class from a famous jammer in the Bay Area a few years back. She used the oven to heat/sterilize her jars, then canned them by the open kettle method with no additional processing. She said that extra heat processing can sometimes ruin the set of a preserve, especially for delicate jellies and marmalades. Her preserves are very tasty and sell very well, but I like the extra safety buffer that waterbath canning gives me.

    While oven canning sounds attractive, it doesn't seem like the same processing times would apply to oven canning compared to waterbath canning. Water is a much more effective conductor of heat than air is, so it heats jars more quickly and more evenly than the oven. The factor I'm thinking about are those few minutes between when you put the filled jars into the waterbath and when the water comes to a boil. In a waterbath, when it starts to boil it most likely means that the jars are now at 212 degrees. How would you know when you reached that temperature with jars in the oven?

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  9. Fab post. Thanks for all your research. Need to try this just so's I can tick it off the list.

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  10. such a great post! i have to mention, my mom taught me the open kettle method (which she used for all of her jam through my whole childhood) and I used it until just a few years ago, and- not ONE bad jar. not a SINGLE ONE. so.... i don't actually know what that means. I still think open kettle is fine if you do it properly! (hot sterile jars, hot sterile lids, piping hot jam)

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  11. oh, so what i meant to say there was bring on the alternative methods!

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  12. In the UK we always use the open kettle method for jams and marmalades. Regular recipes call for high amounts of sugar as the preservative and that all works fine until you start messing about freestyle and wanting your jam less sweet. I was mortified when my morello cherry and whitecurrant jam, entered in the village show last summer, came nowhere. Wondering if the judges had actually sampled it, I opened the jar to find some specs of mould on the top!!!!!! Canning rules now as far as I'm concerned. Suppose the oven method means you could use regular jam jars with screw tops rather than canning jars, which cost a bomb here?

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  13. Great post I like Libby took the class at June Taylor and she never even put the jars back in the oven. The problem I had was I only have two hands and it takes two or more people to get the tops on quick enough while they are at the right deezzgrezz. Also like Kaela said the oven goes on and off but the heat is regulated....Habit we all are creatures of it. And I found that when we get to a new way of doing something we do it and until we feel completely comfortable the Bath works just fine...thanks for the share ....

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  14. interesting. I have not tried oven canning yet so have no opinion. but the jam looks delicious!

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  15. Let's clarify here, in terms of safety, i.e. botulism: if you are canning a nicely acidic fruit jam or marmalade, there is essentially NO difference between open kettle, water bath and oven canning. Botulism spores are not killed at 212 degrees, which is the highest temp that either the water bath or the oven will achieve. Botulism spores, however, are essentially inactive in an acidic environment, so it's the acid in the fruit that keeps your jams safe, rather than the method of sealing your jars.

    In this instance, the differences in water/oven/open kettle are all about achieving a good seal and preventing mold. Mold won't kill you - but it's pretty gross. I tried open kettle for a few recipes, but found I had some seal failures within a few months (which has never happened to me with water bathed jars), and spoiled jars. Now I routinely water bath high-acid preserves simply to ensure a good seal. But I don't think that any one method is the be-all, end-all; if you find a method that works for you, and routinely results in little to no seal failure, I say go for it, as long as it is a HIGH ACID preserve. That's the important part of the equation.

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  16. Really interesting post! My grandmother has been making jam for ages, and it's interesting to remember how she used to do it--definitely not the recommended approach today, but at the time it was the prevailing wisdom. As I've said a million times, I'm a little freaked out about not being 100% by the book on things like food preservation, but it does make me wonder, especially when there is so much variance on things, even country by country. Spoilage concerns aside, I think the idea of an exploding jar of jam is enough to put me off, though.

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  17. Gloria mentioned something that I think is a big point in favor of oven canning (even though I'm not yet sure it's something I'll adopt as a regular practice) -- you can use professional-grade, screw-top lids instead of two-piece lids. That really expands our options for jars.

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  18. Thank you all so much for commenting! And for commenting more than once.

    Livia - Indeed. Hot freaking stuff. See Shae's comment.

    Kaela - Thanks for the thorough response. And yes, ovens vary wildly. Mine included. I forgot about that. Duly noted. And yes, please please only high-acid fruits. No figs! And I've done open kettle numerous times and only once they got funky. Still, it's easy enough to ensure not throwing something out. I've never had a problem with a BWB.

    Wendy - I do too! The water bath must be tough for you. I really think most small companies use the oven approach. Is that true?

    Denise - Good point. I think if you're not doing too much canning, it's best to stay with the tried and true. But if you're cranking out a lot, you have to question the quicker methods. And I'm flattered you'd ask me for advice!

    Meg - And thank you too! I think it's worth a go. Especially for a high-acid marmalade.

    Shae - Yes, I remember your oven canning comments! I think I heard it first from you, but no you weren't the friend who loved it. And thank you for bringing attention to Gloria's comment!

    Denise - that is so cool that you have such provenance in canning! Let me know how it comes out!

    Libby - Very good point. I guess you might not know, but if the jars were in the 250 oven sterilizing for thirty minutes prior I would say they would be close? No?
    Interesting on the open kettle method for sale! I'm sure it happens all the time. Read Christine Ferber's books. No processing at all.

    Caroline - Great story. Love it! Your moms sounds cool.

    Gloria - Thanks for sounding off on this. Yes, the hot water bath is not something you ever used to do, right? I really wonder about the lid issue. How to large companies use those lids? I want a factory tour!

    Lani - Thanks for the comment! Yes, you are right. Creatures of habit are we.

    Eve - thanks! I've been meaning to ask you about your fig "stick." : )

    Sara - You know, as I get more into all of this, I become a little more freaked out, when I should be less freaked out. I guess it comes from having to feed the little one. Another person with a grandmother who preserved. Wish I coulda talked to my g-rents about it!

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    1. I make fig preserves, but add lemon and citric acid to make them more acid.

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  19. I don't do any oven canning because I know from roasting meat that oven temps don't correlate to internal temps.

    I want the assurance that the internal temperature of the foods I'm canning exceeds the temperatures that harmful bacteria can exist.

    Oven canning doesn't provide that assurance.

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  20. I will say, that I find it interesting, we as younger women are getting back into the canning swing of things.. and our mothers and sometimes grandmothers (at least mine) got away from it. IN part due to the failures of some of the previously accepted techniques... melted wax on the surface anyone? That being said, I also think that the canning "authorities" had to write for the lowest common denomenator ie.. well if they make more than one of these mistakes it could be dangerous so lets "outlaw" all of the most questionable techniques... The other thing to keep in mind is the shallower bump on the new canning lids will ping with much lower pressure than the older bigger(deeper) bumps. So you could get that that ping with lower temps and not have as strong of a seal as if you did a water bath and think you were safe(i am thinking of open kettle rather than the oven method)Though I can seriously see the benefit, if you dont want over processed mushy fruit.

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  21. The lawyers make the rules, and the food police scare the pee-waddin' out of us if we dare vary from the policy. Drives me nuts, but then again I am old.

    I have been making jam since 1964, using exclusively the "inversion method". Hot jars, lids and jam, turn the jar over for 15 minutes, and then return to upright. Ping, ping, ping. Never had one jar go bad. And, contrary to my ex-husband's assertions, I ain't dead yet!

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  22. I don't really have an opinion on oven canning, and I will have to mull it over before I decide where my feelings lie. I have only thought about it in terms of "dry canning," ie. canning dried goods for long term preserving.

    But it is so interesting to me that we can have this conversation on the internet. Our grandmothers or great grandmothers may have done it this way or that way, but what opportunities did they have to discuss methods with hundreds or thousands of other people? It's an exciting and fascinating time to be alive. Thanks for sharing this, Julia.

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  23. NO! It's against MN regulations....only water bath and pressure canning are recommended as safe canning methods

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  24. Heya Julia--delighted to see this post. But I would like to clarify my comments. I believe I said I would think this is OK for *hot* fruit, particularly sweet, acidic cooked things (jams and chutneys). I don't this is a particularly wise idea for whole objects (like, say, peaches). There are two separate problems. There is, of course, the "it will never get hotter than 212 inside the jar" problem. But there's also heat circulation. Water is a much, much better heat conductor than air. My concern is with whether the stuff inside the jars ever hits 212. With something like a jam, or a chutney, that's pretty much a liquid and that you've already brought to a boil, no problem--a hot oven will keep it at that temperature. But if it's NOT already hot, I don't think you'd get there in any reasonable amount of time.
    Gosh, this comment was long. Perhaps I should take it over to my own blog? :)

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  25. Kari - Well put. Thanks for the comment.

    SapperAngel - Indeed. I love hearing about the grandmother's ways! But yes, it's true. The laws are set to make sure there's no error, so it's easier to just say don't do it. There are real guidelines to stay within with oven canning, and it can get confusing. Hence, my post!

    Kris - That's awesome. Thank you for sharing. I think it's important to do what you feel is best.

    Jess - Isn't it cool? That's my favorite part of having a blog. Talking with a lot of really interesting people. Thanks for the comment!

    Anon - MN? Is that Minnesota? I totally appreciate your comment, even if you don't approve of oven canning!

    Doris - I was realize I made you sound breezy, and that was certainly not the case! Thanks for sounding off on this, and please do a post on it! My thought is indeed regarding hot high-acid fruit jam/jellies only (which makes it somewhat restrictive, right?). I wasn't even thinking chutneys...Oh, I think you'll need to take this one to the goats!

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  26. i love that it is so lively over here! I have not tried oven canning yet but have been wanting to give it a try, and will. to be honest tho, water bath canning has become so routine to me that it's hard to imagine the oven method any 'easier'.

    i do get concerned about overcooked fruit and have taken to the habit of sterilizing my jars first and water bath processing for just 5 minutes on most of my jam, jellies and marms.

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  27. I tried this method after getting the Blue Chair Jam cookbook a few months ago, and I am NOT a fan. With the water-bath method, I've only had ONE jar not seal, ever. With the oven method, I had 4 jars out of 15 not seal in the big batch of marmalade I made. Nearly a third of the jars not sealing? That's just not acceptable in my mind. And they were brand new lids, so I don't think that was a factor. Plus, I found that a loaded up tray of jars was really unwieldy. I didn't burn myself, but I came awfully close.

    I have to say, I love the recipes in the Blue Chair cookbook, but I think it's really irresponsible for Saunders to present this method as utterly acceptable (and, in fact, she doesn't even talk about water bath canning at all), when there's so much controversy over it, and every other reputable source I've been able to find recommends against it. I won't do it again (although I probably WILL continue to pre-sterilize my empty jars in the oven).

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  28. I'm squarely in the camp of "nuh uh, no way, never" when it comes to canning in a way that's not approved by leading home food preservation scientists. We put too much time, money, and effort into our canning to risk it going bad, even a single jar, and our loved ones are too precious to risk their health with spoiled food.

    It's BWB and pressure-canning for me. I don't care how convincing the argument for "alternative" methods might be, and "neither Grandma nor I have ever killed anyone" is not a compelling argument in this matter. As far as I'm concerned, there's no discussion.

    If you're a new canner, trust only the Home Food Preservation website for guidelines and never trust what any blogger, author, or relative says that may contradict it.

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  29. Tigress - It is lively, right? I totally do the same thing, regarding the five minute rule. You know that's not condoned by the NCHFP either! Water bath banning is totally routine for me. I think this procedure would be helpful if you were making large batches, which I don't.

    ChrisC - Good comment. Thanks for letting me know your experience with it. I agree with you. When I first caught wind of this method I was really surprised that BCF didn't discuss it any further. And yes, strange that she never even discusses water bath canning. But there are many, many canning books that don't go into safety (think Mes Confitures by Ferber) or even recipes that don't seem to be tested for safety.

    Interesting idea on sterilizing in the oven...

    Jenn- Well put. And I absolutely agree, if you are a new canner stick with the pros!

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  30. maybe i would try this if i had any faith in our stupid gas stove. There are too many cold spots inside for me to feel like this would be ok- though we go through jam so dang fast most things would not have time to spoil...i am pretty cautious though since i am new to this, and because the one time i went "off book" and did the inversion method I lost 2 jars of applesauce..(ok when i say lost you should read opened say some mold, skimmed it off, heated the whole thing to boiling again and served it over pork to my mother in law)

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  31. I meant to comment after I read this, and didn't until I am now on a keyboard and not my phone... ANYway.

    I liked reading all of these comments! I really enjoyed reading the Blue Chair Jam book, and also was surprised that Saunders didn't refer to water bath canning at all, or talk about any issues that the government tells us may be unsafe. But the thing I was most surprised with is that she said that she cans all of her jams (I assume for her business as well) this way.

    If small business are able to sell oven-canned products, but it is deemed unsafe for home canners something seems amiss - and I kind of agree with Kris Watson above... we don't make the rules! (and I remember inversion canning the first several times I canned strawberry jam, even after my Mom had given it up!)

    That said, I really did like using the oven method. I have an electric oven. I loved being able to sterilize in there - (and will sterilize this way from now on I think), and because I have a small kitchen and no exhaust fan I LOVED that it didn't feel like a sauna in here. I canned the lemon marmalade, and had 10 out of 10 seal just fine, no exploding jars (or even the bubbling up of jam like she said may happen). Like Tigress said, I didn't feel like I canned. It didn't seem as labor intensive or something - and it was so quiet without that boiling water. I don't think I would can anything other than high acid/sugar fruits this way - but may give it another go come strawberry season. The Saunders strawberry recipes looked mighty good too....

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  32. Regina - I'm beginning to realize that my oven is way too cranky for this method. Lately it's been really freaking out. And good move on the applesauce!

    Rebecca - Thanks for the comment--I'm a little late to respond--but you are right, that it is not okay in every day use, but companies use it seems very strange indeed. I'm sure if the canning thing continues in its popularity, this might be addressed. Or not? Who knows? But what I do know is this: strawberry season is soon!

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  33. Whoa! I had just heard of oven canning & landed here via google... i'm a newly interested gal in canning and it's so funny that I would be attracted to such a hot topic at the beginning of my preservation quest :)

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  34. Hi Sadie - Indeed! Make your own choices for sure, but I'd say it probably wouldn't be a bad idea to start out with regular water bath canning until you completely get the hang of how canning works! Good luck, and thanks for stopping by!

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  35. The way my Mom described my Grandma's oven canning, is that the jars were filled with fruit/vegetables first, then the sealing cap and ring were put on loose, then put in the oven until the contents boiled, then tightly sealed. She eaid they never had problems. This was in Riverside, CA in the 20's and 30's - they would buy fruits and vegetables by the "lug".

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    1. Hi Anon- That's so interesting! Riverside, CA must have been a very different place back then!

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  36. My mother now, 90, canned tomatoes in the oven for years, the exception being she did NOT preheat the oven. She put the filled jars, with lid and rings on a baking sheet in a cold oven, put the temp on 325 for 30 minutes, then turn the oven off, and leave the jars until the next day. I have canned this way and took the jars out some 6 hours later, and they were fine. BUT she NEVER opened the oven door when the oven was still hot to the touch. The tomatoes are beautiful and whole when done this way. She added 1 teaspoon salt per quart. Happy Canning!!

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    1. Hi Ginna! Thanks for stopping by and taking the time to tell such a great story! Happy Canning to you too!

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  37. Why would the stuff inside the jar have to reach a certain temperature? It's already cooked ! Only the jar itself needs to reach a certain temperature and glass heats up QUICKLY !

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    1. Um, because we aren't eating the jars.

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  38. I grew up on my mother's oven canned raspberries, pears, peaches, apricots and apple sauce and now can these in the oven myself ( I am 53). I also oven can pickles - bread and butter and dill- and pickled beets and beans, and canned tomatoes- and have never had problems. As long as everything is sterilized, lids, jars and liquid, either the sugar syrup or the salted water/vinegar are boiling hot I have no mould problems and a good seal can be achieved. I put the hot full jars into a cold oven, set it to 225 F and once the bubbles are starting to rise in the jars, take them out using hot mitts and put the jars onto a dry wooden board to dissipate the heat so as not to shock the jars ( they will break if you put them onto a cold or wet surface.) I put as many jars as I want into the oven but try to use all pints or all quarts. I only use canning jars. I have never been burned or had a jar break.

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    1. Thanks for you feed back, Anon. It's always good to hear these stories!

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  39. My mother-in-law canned all her life and always used the oven for tomatoes. She would put the clean jars, lids on and full of tomatoes & liquid - into a 9x12" cake pan with hot water in it, oven 250. She could watch for when the water in the cake pan was boiling, let the jars boil for five minutes then just leave the jars in the pan until the water cooled down and it could be emptied without danger of getting burned. You could hear the lids popping, almost at the same times. I used this method during the years we had a tomato garden and it was easy to keep up when I worked outside the home; just do enough jars each alternate day as they ripened.

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    1. Love hearing these stories, thanks for commenting!

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  40. In all the articles I have read about OVEN Canning, most canners use it for DRY foods like flour, spices, herbs and dried fruits and vegetables. The reason they use it is to keep bugs from getting to this items like weevils and such. I see it as a much better method for dried foods that only need to have an oxygen reduced storage container. This would save having to buy oxygen absorbers for other storage methods like gallon cans you cannot reuse or plastic buckets with liners.

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    1. Hello, Anon, yes indeed I have heard of the oven used for these methods. Thanks for mentioning it!

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  41. I can using the German Weck jars which the food police don't approve of either. They are so much more attractive as food gifts and I never have a bad seal. They have been used in Europe for many years. Are German food scientists not as smart as American food scientists? When I take the clamps off I can tell if I have a seal. Three months later I can instantly tell if I still have a seal. All to say I often wonder if Ball jar pays for some of this American research. I'll try oven jar sterilizing but I'll sterilize my glass lids and rubber rings in boiling water and process in a water bath just because I'm not sure about rubber rings in a dry oven. I also love my huge Weck electric canner with the temp dial. Now if I could just figure out how long to water process Blue Chair Jam's recipes so they come out as fresh tasting as with the oven processing.

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    1. Mary, I love that you have one of those electric canners! I'm so intrigued by them!

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  42. I realize it's late to be adding to this conversation, but there are a few things I would like to say.

    First of all, the botulin toxin is real and people can die from it. Clostridium botulinum spores need four things to grow: an ambient temperature, an oxygen-free environment, a low-acid environment, and a product that has over 35% moisture. Without these, the toxin will not grow.

    Jams, jellies, pickles, etc., with their high-acid profile, are safe from Clostridium botulinum by their very nature. We preserve these to keep them safe from other bacteria and mold. Therefore, they do not need the 240-degree temperature that low-acid foods need, and 212 degrees is more than enough to kill any spoilers.

    To say that food in a jar can only reach 212 degrees in a boiling water bath or in an oven is to misunderstand physics. It is true that water boils at 212 degrees. As it goes above that temperature, it turns into a gas (steam) and takes on dramatically different properties. The water itself can only reach 212 degrees. The inside of an oven, where hot air is the heating medium, is another story. Air is already a gas and operates under different principles than water. Air CAN be heated to very high temperatures, certainly higher than 240 degrees.

    If you use a pressure canner, you can get your temperature up to 240 degrees because the contents are under pressure, which changes their nature. The steam cannot escape, and thus builds the pressure and the temperature as well. A pressure canner is one way to safely can low-acid foods. An oven is another. While the oven is not pressurized, it can easily reach very high temperatures and cause food temperatures to go way up as well. If food is already boiling when placed in the oven, it will not take long to get it up to 240 degrees and the required 15 minutes held at that temperature to kill the Clostridium botulinum spores. It is the temperature that kills the spores and not the pressure.

    It also bears keeping in mind that when closed jars are placed in an oven and heated, they also build their own pressure inside themselves. The food/air/steam inside the jar cannot get out and, thus, pressure builds. This is why occasionally a jar will explode in the oven, although usually that occurs because the jar already had a very fine nick or scratch in it.

    One other thing I'd like to point out is just because water can only reach 212 degrees on a stove top does not mean that other liquids are confined to that measure. Anyone who has made old-fashioned jam or jelly knows that you must heat your product to 219 degrees or 220 degrees, respectively. How is that possible on a stove top without pressure? It's because a catalyst has been added to the water in the mixture (i.e., fruit, etc.) and changes the nature of the substance. So, yes, foods can be heated on the stove top to well above the boiling point for water. The same can occur for the foods in the jars in the oven. They are not confined to the boiling point of water because they are not water.

    Having said all of this, use your head. Be scrupulously clean and do your research. Do not allow scare tactics to frighten you, and do try to realize that our large government organizations have their own agenda and you might not be part of it. Think.

    Melanie

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  43. Just stumbled here as I tried to find info about using oven. I just used it for a large batch of strawberry jam and add my 2 cents in case someone else wanders here and sees this old discussion (and I pinned this!). I used it yesterday for steamed juice (...not fresh juice as it was steamed, but I don't know what they call it in English...). Nothing has exploded...

    First, thanks for Melanie for the helpful information in the previous comment. It is very much in line with what I have studied about botulism, as well as common sense. Some points to add:

    The oven method described in this blog post is not a "standard" or the only way to utilize oven. 1) You can use the oven to sterilize the jars - my mom uses this with the open kettle method. 2) You can use it to achieve a seal after you have filled the jars - however if you fill them with hot jam to the top they will seal on their own as the jam cools. 3) You can use it to kill bacteria and increase the likelihood of sealing. 4) You can use it to cook the product in addition to purpose 3 (I found a lot of discussions by fishers who make interesting canned fish meals and spreads this way). With purpose 1 it would be practical to bake the jars but boil the lids. With purpose 2 you simply re-heat the closed product briefly as you do in the water boil method. With purpose 3 you continue baking longer, to ensure bacteria dies. With purpose 4 you cook as long as you need to - according to recipes I saw the whole small fish became soft after 4-6 hours (the "bones" of the small fish).

    The American system assumes you have a lid that is in two parts. I've never seen those in Europe. I use Italian jars made by Bormioli Rocco that are beautiful and available easily. Also very practically designed. Starting cost is quite a bit, but if you continue making jams year after year it is not bad at all for such a functional product. You can buy new lids replacements. If you are going to store the jars in a cold place, you are fine with open kettle and do not need new lids every year. A brand new lid should be used when you want to make a sealed product than can be stored in room temperature. I've been doing this as I don't have a cellar yet but I want to make more jams and juices my fridge can take. So I baked my jam for half an hour in 125C. I put the filled jars in the cold oven so they heated smoothly, and counted time from when the oven reached the temperature. I have a new oven and modern air system so I'm sure it works. I saw the jam making a little bubbles like you would see in a glass of soda (but even smaller) and I turned the heat off and they will cool there in the oven until next morning. So I only deal with warm not hot jars and jam - no burns. It is possible I am overcooking my jam this way but so far I haven't got enough "official and precise" information about this process to make me compromise what my common sense is suggesting. I note the American instructions tell precisely what to do but do not explain why and what happens which makes me uncomfortable. I mean the style is authoritative without building full understanding of what's going on.

    About acid: I've learned somewhere that some lemon juice should be added to red jams (strawberry, rapberry) to preserve colours. First time I made jam it turned brownish red but after learning this trick my jams are bright red and lovely. And based on what Melanie and others wrote, it seems to help with keeping the jam to stay good, a bonus I was not aware of.

    Saara

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  44. This is fantastic. I have a lot of food in storage, but recently had a battle with grain moths, fortunately just in my cabinets and not in my storage area. But because of that it has become a concern for me, I’ll definitely be doing this!!
    My blog

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  45. Awesome post.
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    Cabinet ovens

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  46. كافة خدمات شركة تنظيف منازل بالمدينة المنورة مقدمة من شركتناحيث نسعي للوصول الى ان نكون افضل شركة تنظيف منازل بالمدينة المنورة مقدمة حيث نقدم كافة خدمات التنظيف داخل وخارج المنازل بالمدينة المنورة هل تبحثون عن جودة الخدمة المقدمة من شركة تنظيف منازل التي تبحثون عن خدماتها فقط اتصلوا بنا حيث نبذل مجهودنا لنقدم افضل خدماتنا لكافة العملاء .مستخدمين في ذلك كادر من افضل وامهرعمال التنظيف الداخلي والخارجي للمنازل بالاضافة الى ماكينات التنظيف من الداخل والخارج للمنازل بالاضافة الى اجود المنظفات المستوردة لدينا في تنظيف منازل بالمدينة المنورة.

    تنظيف منازل بالمدينه المنوره

    شركة تنظيف منازل بالمدينة المنورة فنحن من اهم شركات النظافة حيث تستخدم انواع كثيره من أفضل أنواع المطهرات والمنظفات والمواد الخام للنظافة ونقوم باستخدامها فى كافة أرجاء المكان داخل شقتك مثل الأحواض وحوائط المنازل والأرضيات والاسقف والرخام والسجاد والألواح الداخلية والخارجية والمكاتب والمبانى والزجاج والخزانات وجميع انواع الأثاثات ,
    شركة تنظيف منازل بالمدينة المنورة
    الى جانب ذلك تنظيف منازل بالمدينة المنورة تقوم بتنظيف المطابخ بكافة انواعها المختلفة مهما كان احجام المطابخ كبيرة ام صغيرة. شركة تنظيف منازل تهتم برضاء العميل قبل اى شى فاذا أردت أن تتخلص من كافة الأتربة التى توجد داخل الشقة الخاصة بك فلا تتردد فى الاتصال بنا فى اى وقت طوال اليوم ,
    تنظيف منازل بالمدينة المنورة
    فسوف تقوم تنظيف منازل بالمدينه المنوره بمساعدتك باستخدام احسن وأفضل المواد المنظفة وسوف نساعدك على افضل بريق واعادة البريق واللمعان الخاص بك , فقط اعتمد علي شركة تنظيف شقق بالمدينة المنورة واحصل على أفضل الخدمات التى تريدها بل افضل من الخدمات التى تريدها وتتوقعها .


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