flowerbug
Sustainability Master
you need a reliable oven which doesn't vary the temperature by much. if you don't have a thermometer to see what your oven is actually doing you would want to get one to make sure you're not overheating because that can cause issues (like jars breaking in the oven or blowing off lids/rings).
in recent years mostly what i have oven canned are:
tomato chunks, tomato juice, dill pickles, bread and butter pickles, three (or more) bean salad, pickled beets, apple sauce and various jams (grape, strawberry, blueberry, peach).
note all of these are high enough acid foods that they do not require pressure canning (when done properly - i'm very picky and clean about how i do things so we don't have many issues with items spoiling).
in the past few years Mom has oven canned beets, but since they are not high acid i didn't eat them and it turned out she didn't eat all of them either. we ended up feeding them to the worms. not because they were bad, but because she just didn't like them any more (her tastes have changed). we no longer grow beets or can any of them (pickled or regular).
when i was a kid she oven canned everything we put up (all the stuff above plus chili sauce, beans, potatoes, carrots, etc.).
the basic method is to get the jars warm, hot pack everything (leaving some head space), wipe down the rim and then put a warmed up lid on and a ring tightened hand tight plus a quarter turn or so (it's a certain feel you get used to when you've canned a lot).
then depending upon what is in the jar adjust your processing time in the oven. most high acid items i'm only processing enough to get the seal to set. so that is 250F for about 15 minutes. tomatoes or things which aren't going to be used in the next year i might go twice as long. if the contents have cooled more i will go as much as 45 minutes. i don't want the contents to boil much beyond a few tiny bubbles. the main idea is to heat the air in the headspace so it expands and then vents around the lid. i have had things boil a bit more but that isn't what i want to happen. i just want the seal to be set.
what is nice is that if you've gotten the contents hot enough and the jars are warm to hot then it doesn't take much additional heat to get the pressure to vent from the jars and then for them to seal.
while packing jars and putting them in the oven i will keep the oven at 225F. i can fit 24 quarts at a time in the oven. that is the biggest reason i think oven canning works so well for us, because we're not having to heat up a lot of water, we're just heating up the contents and then the jars in the oven after they've been filled and sealed.
after the time is up then we turn off the oven and leave them to cool before moving them too much. i rarely do more than one batch at a time anyways, but i've also managed to move them while hot without issues other than making sure i have some good oven mitts to grab the jars without tipping them too much.
you can blow up jars, if you don't notice a crack or a chip, i've also had some lids not work and they end up blowing off the jars if they don't let the air escape from the headspace. i've never had a problem with Ball lids doing this, but i have had a problem with one batch of generic lids where i ended up taking them back and exchanging them for others. those worked fine.
it can be a mess in the oven if a jar breaks. if you have enough room underneath to put a pan down you can do that. i've not bothered because it happens so rarely to us. we've had perhaps two or three jars break since we've been canning in this house.
as for what to do with low acid foods and oven canning. i won't do it, but Mom will. they go a long time and i don't like the results. if i want mushy vegetables i'll just buy the cheapest canned stuff at the stores. i hardly ever do this now as i'd rather buy frozen veggies if they are available. the idea of running an oven in the summer to do beans for two or three hours just doesn't appeal to me at all - but that's how Mom used to do it all the time.
as for how many jars we normally do a season. last year we did a few hundred quarts. that wasn't as much as normal (mostly dill pickles, tomatoes and bread and butter pickles). this season i expect we'll be doing 300-500 quarts total. we planted a lot of tomatoes. we won't be doing any pickles - we have enough already. Mom thinks she's going to do some beans but i'm going to try to talk her out of that or see if we can do some bean salad quarts instead (which are pickled sweet and sour). higher acid things i don't worry about.
the reason i talk about low acid and high acid items is that botulism poisoning occurs for items which are not acidic enough and if they've not been properly processed to get them to the high enough temperature needed. for low acid items this means pressure cooking and you can't do that with oven canning unless you have some kind of fancy oven i've never heard of before.
high acid items like certain varieties of tomatoes or pickles they can be done in a boiling water bath and that's the same temperatures reached in oven canning.
