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I'd always assumed that things cooked sous-vide (which translates as 'under vacuum'!) needed to be under a good vacuum for the most efficient heat transfer into the meat, since air is less convective than water. I also thought there might be a hygiene issue with having the meat exposed to the air in the bag.

However, in the video on this Kickstarter page (at around 1.00), she simply puts the steak in a sealed Ziploc bag and then into the water bath, without evacuating the bag. So, are my concerns unfounded?

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up vote 7 down vote accepted

Yep, Ziploc bags are fine although make sure you have ones that are appropriately heat sensitive for whatever temperatures you'll be cooking at. There's a good guide on the Cooking Issues blog:

http://www.cookingissues.com/primers/sous-vide/part-ii-low-temperature-cooking-without-a-vacuum/#sectionII3b1

  1. Fill a container with water deep enough to easily submerge your food and bag.

  2. Always add some sort of liquid to the bag –fat, stock, sauce, etc. The liquid is necessary to fill the gaps around your food and expel the air from the bag.

  3. Add your food item. A significant advantage of Ziplocs over vacuum bags is that the food can be added to the bag hot. All vacuum bagging procedures require your food to be cold (more on that in the upcoming vacuum section of the primer). If you are searing meat and adding it directly to the Ziploc bag make sure the surface of the meat is below 100˚C (212˚F) or the bag will melt. Be especially careful to not touch the bag with a hot set of tongs or spatula.

  4. Close the seal of the bag almost to the edge, leaving the last portion of the seal open –make sure you have correctly sealed the bag. Put your finger in the corner to make sure that part of the seal is open.

  5. Carefully immerse the bag in the water starting with the closed corner, not the open one. Make sure you do this step carefully, allowing air to escape up and out of the open corner.

  6. Just as the open part of the seal is about to go under the water, close it up.

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Regarding steps 4-6: it seems as though this technique uses the water pressure to partially evacuate the bag. So it seems like a vacuum is necessary, though it can be achieved to an acceptable level without a vacuum pump –  Benjamin Hodgson Aug 9 '12 at 22:40
    
Perhaps, but is it really a vacuum if there is never empty space? At least, I wouldn't quite consider it a vacuum in the sense that a bell jar would be. –  Ray Aug 10 '12 at 1:35
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By the way, your point about sous vide being nonsensical without a true vacuum is spot on, and why the folks at the linked site (cookingissues.com) seem to prefer the term "low temperature cooking". Admittedly, I find that term a little too imprecise exactly where "sous vide" is a little too precise. Maybe you call it "water bath cooking", but that lacks the punch of "sous vide". All the traditional forms of cooking have great names like "fry", "bake", "boil", and "grill". How could "water bath cooking" ever compete?? –  Ray Aug 10 '12 at 1:38
    
Grant Achatz uses this technique to cook thanksgiving dinner in a series of youtube videos (e.g. youtube.com/watch?v=PM3O1xRJ4XU ). If you're not using a liquid, I'd recommend the zip-lock vacuum bags, which Michael Ruhlman uses. They're also good for freezing leftover portions of food. I've used them to sous-vide lamb loin (in a styrofoam cooler) with excellent results. –  Steve Aug 10 '12 at 4:23
    
I would venture to say the answer to that question very much so depends on what your finished product should be like. For example, something like a steak or pork chop a strong vacuum makes the cooking more efficient and has added benefits, however for something that's more delicate like a fish or chicken breast too tight of a vacuum can adversely effect the texture of the finished product. So yes, removing excess air is necessary to be more efficient but too much vacuum can also be bad. –  Brendan Jan 29 '13 at 16:26
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For cooking a portion of meat sous-vide; use a zip lock style bag slightly bigger than the meat. Add the meat and zip the bag closed, but leave a very small opening. Then scrunch and roll the package with your hands to remove all the air, and then close fully the zip. Be careful not to tear the bag

Trying to do this in a bath of hot water is just silly. Your hands can exert much more pressure than a few cm of water could ever do

If the meat has bones sticking out; either use a sous-vide grade bag, or put a small strip of plain brown cardboard over the bone protrusion. After water bath cooking, make sure to discard the cardboard before finishing

As Joe mentions, if you have a cooking liquid to add to the bag, this task is even easier. Just fill the bag with meat and liquid, then let the bag rest on the bench until the liquid just starts to overflow the zip, and then fully close bag

For light foods, or foods where you can't get all the air out without the use of a vacuum pump; use a slightly larger bag than normal, and place some heavy objects in the bag (stainless steel food weights, or teaspoons) with the food. When this is placed in the water bath, the food will remain under water and in close contact of hot water/bag boundary, and the contained air will form a bubble at the top of the bag

I have used zip lock style bags, and haven't been too fussy with air extraction, and have had excellent results with sous-vide cooking

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The pressure of your hands may be greater (of course it is), but the pressure from the water is even. It need not be hot. –  Ray Aug 10 '12 at 2:32
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@Ray : but if you have some liquid in the bag, all you need to do is squeeze 'til the liquid comes up to the bag closure, then seal, and you're (mostly) assured that the bag's air free. (I say 'mostly', as there could be trapped pockets of air). A water bath's only going to exert a little pressure depending on its depth (~3kPa/foot), while a vaccuum would be near 100 kPa (depending on elevation). –  Joe Aug 10 '12 at 2:50
    
@Joe updated, thanks –  TFD Aug 10 '12 at 3:50
    
@Ray Why would a low, but even pressure be of benefit? A normal sous-vide portion is not much bigger than what a hand can compresses at the same time. So in practices you find the hand does an extremely effective job at removing air from the bag. Also the bag tends to stick to the damp meat surface, thus once compressed it tends to stay put, and not let air back in –  TFD Aug 10 '12 at 14:48
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In my experience, squishing by hand does not remove enough air to prevent flotation, whereas the submersion technique normally does. But hey, if it works for you, go for it. –  Ray Aug 10 '12 at 16:45
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