I'm really interested in discussing the concept of shelf-stable canning of acid food products with an immersion circulator. This has come up in the forum a few times in the past without really going anywhere.
Home canning of acidic foods with a pH of 4.6 or less is typically accomplished in a boiling water bath that covers the jars. The processing time both effectively pasteurizes the jar contents and forces out enough air to create a vacuum when the jar cools, which provides essentially indefinite shelf life until the seal is broken. With acidic foods there is no concern about clostridium botulinum, but the jars must be processed for long enough to eliminate any spoiling bacteria, molds, and yeasts that may be present. The National Centre for Home Food Preservation, various extension offices, and jar manufacturers like Ball provide a range of tested recipes and processing times for various products and instruct home canners to not deviate from them in any way.
@Chris_Young_80640 says he contacted the USDA while working on Modernist Cuisine and was told they couldn't provide a list of target pathogens because the water bath processes they recommend are based on data so old it has been lost, so
he wasn't a ble to create any canning guidelines for MC. I have been going through food safety resources and came across some interesting links, including a 2015 study of steam canners that discusses core temperatures and lethality as well as target pathogens in some depth. I also note that Douglas Baldwin has stated the sous vide pickle recipe should effectively pasteurize anything with a pH of 4.0 or less, which covers quite a lot of canned fruit products.
My interest in developing processes to use with immersion circulators is mostly with respect to certain fruits which tend to violently expel air and expand and press on the lids when canned in boiling water. However, there are many other products it could also apply to which benefit from cooler processing. Personally I will never again process pickles in a boiling water bath because the quality of the product is so much better with the ChefSteps sous vide pickle method. As an example of something I would like to expand this concept to, stewed rhubarb can be very difficult to can because if it isn't boiled soft beforehand and cooled for a long time in the canner, it will often leak or even pop off a lid when exposed to room temperature because it expels air so violently. In an immersion circulator bath it can be processed at a lower temperature for a much longer time (e.g. 190°F for 90 minutes), which allows it to gently expel air and significantly improves the quality of the product. Having read the steam canning study and done some informal testing of internal temperatures, I am confident this is perfectly safe.
The pitfalls of any general guidelines are things like ensuring adequate heat penetration as well as pH when some components of a recipe are not acidic enough on their own. It is also essential to ensure enough air is expelled, which is difficult or potentially impossible with many foods at very low temperatures like what is suggested in the pickle recipe. However, I think this process could easily be applied to simple canning of items like the rhubarb I mentioned.
I'd love to discuss this further. Here are some resources I gathered on the subject.
ChefSteps sous vide pickle recipe:
NCHFP guidelines for safe canning:
Healthy Canning discussion of principles of water bath canning:
Healthy Canning discussion of pH testing to ensure correct acidity:
FDA resource on testing and target pathogens and typical pH of various food products:
Journal paper testing steam canners:
Old ChefSteps forums posts:
