My girlfriend and I were talking about the summer produce season approaching and hit on the idea of canning sous-vide. That is, rather than sterilizing by high heat for a short amount of time, you could sterilize with low heat for a large amount of time with a sous-vide setup. Particularly in the case of vegetables, which don't start to cook much until around 170 degrees, we thought that if we could use a lower-temperature process for a day or so we could can pickles and jams without having to boil them half to death. So: why is this stupid?
Here is why it's stupid:
- Sous-vide doesn't get hot enough to kill botulism spores. Low acid foods will be very dangerous.
- Boiling is required for a strong seal on canning jars.
- All pectin jellies I have seen require boiling to set.
High acid recipes often call for processing in a water bath for a mere 10 minutes to seal the lids. Recipes that don't call for the water bath universally call for the product to be refrigerated.
Perhaps high acid foods could be vacuum sealed instead of bottled and pasteurized. It seems feasible but this is not the sort of thing you should experiment with. The failure conditions are catastrophic.
Low heat pasteurisation is common in the food processing industry. They also use many other techniques including batch laboratory testing. Two low temperature techniques are:
Narrow tube pasteurisation. To ensure all food/liquid has been evenly heated and then cooled. Only suitable for food/liquid that can pass through a grid of narrow tubes. Can be as low as 72°C for 15 seconds. Similar to what happen on a dairy farm. Besides juices it is often used for tomato paste and fruit fillings
High voltage electric pulses (PEF?). Typically 20,000 V pulses for a few seconds. Used in juices and meats
None of these are suitable for a home environment, and it would not be worth the risk if you live in an area with a common botulism problem
Most people quite like the "bottled" (canned) taste and texture for none staple foods
Actually, you can use sous vide to preserve food in canning jars. The company "Chefsteps" has a guide on their website. They use an acidic brine, and quote well-known expert on sous vide safety, Douglas Baldwin, who writes: “Distilled 5 percent white vinegar, at about 2.6 pH, is very acidic. Food pathogens can’t grow below 4.0 pH, and vinegar is 25 times more acidic than this. (The pH scale is logarithmic, so 3.0 pH is 10 times more acidic than 4.0 pH.) Cooking or pasteurizing the pickles kills the pathogens that can grow below 4.6 pH, and the vinegar in this recipe is 100 times more acidic than this. For reasons of both taste and safety, our brines contain between 38 and 44 percent vinegar. So as the brine diffuses into the fruits and vegetables, it quickly acidifies them to below 4.0 pH, and so no food pathogens can grow. Since no food pathogens can grow, the pickles are safe to store in your cupboard.” Of course, this does not address making jams.
I ferment dill pickle spears. Many web sites suggest that you can pasteurize fermented pickles in a 180 degree water bath for 30 minutes. I am going to try this with my fermented pickles. I don't have enough room in my refrigerator to store all the pickles I ferment. I feel confident that the salt and lactic-acid from the lacto-fermentation process will be make everything fine.