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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?

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2 Answers 2

Here is why it's stupid:

  1. Sous-vide doesn't get hot enough to kill botulism spores. Low acid foods will be very dangerous.
  2. Boiling is required for a strong seal on canning jars.
  3. 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.

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I would upvote this ten times if I could. Especially important (apart from the health risks) is the pectin gelling temperature. –  daniel Apr 13 '11 at 4:00
    
Per Douglas Baldwin, "a 6D reduction in non-proteolytic C. botulinum requires 520 minutes (8 hours 40 minutes) at 167°F (75°C), 75 minutes at 176°F (80°C), or 25 minutes at 185°F (85°C)" so I disagree with point one. Like with many other safety temperatures, boiling is recommended because it's instant death and doesn't require precision. Sous Vide allows a level of precision that lets you use much lower temperatures than traditional "safe" metrics. –  yossarian Apr 13 '11 at 13:48
    
Also, wrt 3, the pectin may need boiling to set, but that doesn't require that it boils for the whole time (assuming you're adding pectin rather than using the fruit's natural pectin). Bringing to a boil and then finishing sous vide would decrease the total amount of cooking you are doing and still allow the pectin to set. –  yossarian Apr 13 '11 at 13:50
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Hmmmm, actually, I retract the information from Douglas Baldwin. That's only relevant if you're consuming the food quickly as the spores can survive these temperatures and become active again after canning. –  yossarian Apr 13 '11 at 14:02
    
@yossarian- I agree with you. It seems for high acid jam you could boil for a little while to set the pectin (possibly separate from the fruit), seal in a vacuum pouch and pasteurize. Is it possible to test this approach for safety without a lab or electron microscope? –  Sobachatina Apr 13 '11 at 14:42
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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:

  1. 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

  2. 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

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