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How do I re-process unsealed strawberry jam?

I made strawberry jam today and canned it in Ball jars via the Blue Chair Jam cookbook method. For any unfamiliar with this method, you sterilize the jars by leaving them in a 250 F oven for 30 minutes, add the hot jam, put on the lids and return the jars to the oven for 15 minutes more. Once removed from the oven, the seals on the jars activate. However, this time I had several jars that didn't seal. Can I reprocess these jars? I only removed them from the oven about 1 1/2 hours ago. I don't want to compromise the safety of the jam by partially cooling, then reheating in the canning process. What do you guys think? Put them back in the oven or leave them as is?

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Trena added 11 months ago

I've never heard of the Blue Chair Jam cookbook method. When I water bath can I typically refrigerate any jars that don't seal. Perhaps someone else in the Food 52 community has better advice. Enjoy your strawberry jam!

dymnyno added 11 months ago

I wouldn't worry about reprocessing the jars. Jam has a lot of sugar which is a great preserver so the jam won't to bad fast. Just heat the jam and start over with clean jars.

clementinebakes added 11 months ago

I make jam and keep it for a long time in the fridge, but these were intended for gifts in the future. Change of plans?


Abbie is a trusted source on General Cooking.

added 11 months ago

You can re-can but you will need to un-jar the jam and clean the jars, reheat the jam, and use new disc tops to can. Otherwise the safety of the jam on the shelf is compromised. Other wise into the fridge it goes!! I have only used the oven method once and it makes me nervous - I like the sure knowledge of boiling water and quickly popping seals ...

clementinebakes added 11 months ago

Thanks! The last time I did it, it worked perfectly, this time I used a few old jars, and those were the ones that didn't seal. Maybe the edges were chipped and I just couldn't see. I like the oven method for my tiny kitchen, where I don't have room for a canning pot. Thanks for your help!

Trena added 11 months ago

After doing some research on oven canning I've learned that this method is considered unsafe. I've copied and pasted an answer to a question previously posted on Food 52 from ChefOno below who I think spells out the pitfalls very clearly. Please find it below.
The reasoning / science behind abandoning oven canning is manifold:

As suggested, actual oven temperatures can vary considerably from the set point, both due to inaccuracy of their thermostats and from the way they function. Ovens cycle on and off to regulate temperature and there can be a considerable variation between the temperature at which they turn on and when they turn off. The set point can represent the high, low or average temperature -- or none of the above in many cases. In contrast, water boils at a consistent point with simple, known adjustments for altitude.

Transmission of heat through air is inefficient compared to water or steam. Put your hand in a 250F oven and then put it in boiling water if you want a quick demonstration of the principle. So a 250F oven will not heat food to the same temperature as a boiling water bath unless it were to remain for a considerably longer time. And even then it wouldn't if the surface of the food is left exposed due to heat lost through evaporation. Canning requires known times and temperatures to be safe.
ChefOno states:
"Radiated heat from direct exposure to an oven's heating coils has shattered many a jar causing injury, loss of food and one hell of a mess. Blue Chair's desire to return to a simpler time may give some people a warm and fuzzy feeling but could very well produce fuzzy food and a case of botulism in the process."

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