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How often do you need to change the water in your Sous Vide machine? Given food never touches the water I don't think I need to change it every time, but it does seem like I should change it once in awhile. Any rules of thumb?

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I would suggest changing it when you see particles floating in it, it smells off, or you catch pets drinking or playing in it. – SAJ14SAJ Apr 2 '14 at 22:42
The food may never touch it directly, but how sure are you that the exterior of the bags/vessels are 100% free of any bacteria or other contaminants? – Aaronut Apr 2 '14 at 23:38
@Aaronut I think the point was that the water couldn't contaminate the food, not that the food couldn't contaminate the water. – Jefromi Apr 3 '14 at 0:06
I think your constraints here come from legionella danger, not from food pathogen danger. Not so sure what the max safe time for standing water is, though; the basic advice is "don't do it". – rumtscho Apr 3 '14 at 10:03
Thanks All. I was just concerned that the heating of the water then cooling may make it more likely to create bacteria. – Jack Sinclair Apr 3 '14 at 13:38
up vote 6 down vote accepted

The water frequently sits in the danger zone for bacterial growth, and even though it is a sealed bag, fats can migrate through the plastic (not considering contamination to the outside of the bag either from cross contamination or from juices drawn out during vacuuming/sealing).

I would suggest changing the water if:

  1. is looks dirty/cloudy
  2. it smells like anything other than water

Additionally from the PloyScience site:

Occasionally or when a cooking pouch may have leaked, simply replace the water with a vinegar/water solution and run unit at 160°F for 25 minutes to remove any residuals or lime.

So you can probably throw a little vinegar into the water to up the pH and make it more hostile to bacteria (though it will smell up the house when you use it).

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