I'm getting ready to can fig preserves, and read recently that i can put freshly washed canning jars in a cold oven and turn it up to 250 degrees to sterilize the jars. Anyone want to weigh in on this? I'd love to use this method as long as i don't risk making my friends sick.



bhw July 29, 2011
For preserves, you don't really have to worry about botulism poisoning. Canned fruits with added sugar will usually ferment if they go bad and you'll notice this right when you open the jar, if the lid hasn't popped open from the gas pressure that builds up.

Happy canning!

mainecook61 July 28, 2011
Figs from your tree---I am faint with envy here in Maine. Trade for blueberries?
hardlikearmour July 28, 2011
Or gifts for helpful foodpickle friends?
Frontalgirl July 28, 2011
My thanks to everyone! I made the perserves this morning. 5# figs, 6 cups sugar...boil the hell out of it till nice and thick. Added 1/2 cup fresh lemon juice and bits of thinly sliced lemon. Put the jars in cold oven and set to 250 degrees. They were in for about 45 minutes as i cooked the preserves. when I filled the jars they were HOT! I've been canning for years so am aware of the other great bits of advice. :) i processed them for 15 minutes and they are beautiful! The tree is prolific this year so i may be doing this again in a day or two. Gifts for friends will be a jar of figs with a nice sharp cheddar!
Eugenia B. July 28, 2011
According to the USDA, you don't need to sterilize jars that are going to be water-bath processed for more than 10 minutes at sea level (the time increases depending on your altitude). Since jars (with or without food in them) are sterilized when boiled for 10 minutes at sea level (adding 1 minute for every 1,000 feet above sea level), during the course of water bath processing, the inside and outside of the jar, and its contents are sterilized. Your jars and bands just need to be clean, especially on the threads, as per mainecook61 (you should simmer new lids in hot warer for a few minutes before every processing though--this softens the rubberized flange which increases your chances of a good seal). If the food you are canning calls for processing 10 minutes or less, then the recommendation is to sterilize the jars first, by boiling in a water bath for 10 minutes at sea level (adding 1 minutes for every 1,000 feet above). Again, use new lids, simmered in hot water, for every processing.
latoscana July 27, 2011
I think the concern about heating in the oven is that the glass could break and it might not get the jars really hot enough. The Ball Blue Book says not to do it - and not to count on the dishwasher doing the job well, either. But Ball also says there's no need to sterilize if you are going to process the food longer than 10 minutes. Usually, only jellies are processed less than 10 min. So, if processing longer, you need to get the jars heated up (so they won't break when you pour hot liquid in), but don't need to sterilize. Lids need to be heated to 180 for 10 min.
greathill July 27, 2011
Everyone here really sounds like they know what they are doing! But for me, my routine is to thoroughly clean the jars with soap and hot water then I put them on a cookie sheet in an oven heated to 250-300 until I'm ready to fill the jars. I usually do this right before I'm ready to fill the jars so they aren't in the oven more than 15 minutes or so. And I always boil the lids. I hope your preserves come out great! I'm sure they will.
mainecook61 July 27, 2011
Right about tomatoes and figs being on the low-acid side (depending on the variety). Tomatoes might indeed need a tsp. of lemon juice or vinegar in the jar (unless you use a pressure canner), but the sugar in fig preserves is the main inhibitor to bacteria growth. Toxins like botulism are really not a concern in properly canned jams, jellies, etc. Take care to leave only a bit of headspace at the top of the jar (1/4") and to wipe the threads clean with a damp cloth before putting on the lid. Syrup on the threads is one of the main reasons for sealing failure. Jeez, I sound old, but I've been making jam, et al. for a long time.
thibse July 27, 2011
I run my canning jars through a hot water rinse in an otherwise-empty dishwasher, and leave the door closed until I'm ready to use them. It may not be very energy-efficient if you're only making a few jars, but works perfectly for a full afternoon of canning.
sarabclever July 27, 2011
I think figs (and tomatoes) are an exception; in that they are a low-acid/borderline fruit so they have to be acidified a little to be safe.
mainecook61 July 27, 2011
Jams and preserves contain such high levels of sugar and acid that you don't have to worry about dangerous bacteria the way you might if you were canning a low-acid item (like beans, which must be pressure-canned). Before rings and lids, people regularly just sealed the tops of jams with hot paraffin (and some people still do). I haven't tried the oven technique; however, as mentioned in another post, heating jars and lids in the hot water you're heating for the hot water bath you must have to get a reliable tight seal is pretty efficient.
Helen's A. July 27, 2011
I've never tried this. I always boil my jars for at least 10 minutes. I process my preserves in a hot water bath anyways so I have the canner boiling so it's not really any additional work for me. Your technique sounds great, curious to see how it comes out.

BTW - I made a great rhubarb fig jam this spring, highly recommend.
hardlikearmour July 27, 2011
Since the big bacteria you are worried about is C. botulinum, that strategy should be effective. At 250º F you will get a 12-D reduction of the bacteria in 2.52 minutes.
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