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I frequently use the water displacement method to seal ziploc freezer bags when I sous vide. I can get maybe 99% of the air out, but technically the bag is not under vacuum. If I clip the top of the bag to the side of my container, any air pockets that emerge collects at the top, and the meat is entirely in contact with the bag and immersion bath. Alternatively, if I seal the bag with a marinade, there are no pockets of air between the meat and the immersion bath.

I can't imagine that the temperature transfer can be any more effective when vacuum sealed. So why does a site like SeriousEats still suggest that a vacuum sealer is needed for best results with longer cooking times?

update from http://www.seriouseats.com/2016/08/how-to-seal-food-airtight-without-vacuum-sealer-water-displacement-method.html#comments-299859

In the context of food storage in plastic bags, SeriousEats claims, "excess air causes oxidation that can develop into off flavors or promote spoilage." But I never sous vide for the freezer, it gets served when done.

There was a comment that asked if food contamination might occur for cooking times longer than 48 hours, but it was never answered.

What is the science behind this statement? How much residual air is "too much"?

If the bag remains submerged, does not leak, and the food in full contact with the water bath, is that enough to duplicate the benefits of a true vacuum seal?

update 2

Also, what is the scientific impact of trapping small amounts of residual air in a pocket above the water bath? This assumes that there is still a very strong thermal coupling between the water bath and sous vide item.

In the photo below, you can see at least a 2inch gap between the air pockets above water level and the actual short ribs. From a heat transfer perspective, I can't imagine that a vacuum sealed bag can perform significantly better—certainly not relative to a 48hr cook time. Is there a possibility of bacterial contamination?

sous vide bag with residual air above water bath

marked as duplicate by moscafj, GdD, Stephie, Cindy, Catija Feb 16 '17 at 0:40

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • +1 - Excellent question and welcome to this site, Michael – BaffledCook Feb 10 '17 at 8:25
  • Very good question. Personally I would change the title to reflect the question more accurately i.e. that you are asking about the efficacy of sous vide without a vacuum sealer, not how to actually do it. – canardgras Feb 10 '17 at 8:41
  • I agree with it beeing duplicate and the top rated answer there suits perfectly to this question and would also be my answer ;) – Silent-Bob Feb 10 '17 at 12:15
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The main problem I've found is that air pockets can cause the bag to float, causing uneven heating. If your bag sinks, or if you have something to make it sink, it should be fine.

(Note: I find the water displacement method to be kind of a pain and not really effective. I use a cheapo manual vacuum pump, which I got for about ten bucks. It's very slightly more effective, and cheap.)

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The dedicated vacuum sealer makes better seams than the ZipLoc Freezer bag edges. For long duration cooking, this is a big advantage. I have to double-bag when I am doing an extended cook at a higher temp. And working out air pockets is twice as painful with two bags and hot water!

  • I've never had a problem with leakage from a ziploc freezer bag—even when cooking times reach 48-72 hours. – michael Feb 11 '17 at 13:22
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    If hot water is a problem seal your bags in tepid water then immerse them in the circulator bath. – user23186 Feb 14 '17 at 19:12
  • I found that preheating the water to 100F (I.e. Hot tub temp) makes it much easier to evacuate air bubbles from the bag. It is much more pliable at temp, but still not too hot for your hands. – michael May 31 '17 at 12:14
  • @user23186 In my personal experience, air pockets tend to reveal themselves after the cooking has begun. This is especially true when the food is double-bagged. – Keith Payne Jun 1 '17 at 12:37
  • @michael That is a good idea! – Keith Payne Jun 1 '17 at 12:38

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