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Why Ziploc bags are perfectly safe for sous vide cooking

No need to splurge on a vacuum sealer -- cheaper Ziploc bags and water work just fine.

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Food-safe zipper bags work great for sous vide.

Josh P. Miller/CNET

I'm known to go the cheap route whenever possible, so while learning to cook sous vide I used Ziploc bags instead of vacuum sealed bags. 

I have never had a problem with them. They didn't melt, burn or make me sick. Still, though, I had some lingering questions about their safety. 

Too much air?

Some believe that Ziploc bags don't remove all of the air, resulting in less penetration of any marinades and -- worse -- bacteria growth in the food while it's cooking. Is it true?

Probably not. Research has found that it is the temperature you cook and store the food at that prevents bacteria growth, not the vacuum sealing. Plus, if you want to get all of the air out of the bag without a vacuum sealer, you can use the water displacement method to get the best results. 

Here's how:

  1. Fill up your sink or a bowl with water.
  2. Fill your Ziploc bag with the ingredients up to 1 inch (2.5 centimeters) away from the opening and close the zipper almost all of the way.
  3. Submerge the bag in the water, slowly, leaving just the open zipper area exposed. Pressure from the water will force the air out.
  4. Zip the bag closed before raising it out of the water.
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A bag sealed with water displacement. 

Taylor Martin/CNET

Will chemicals leach into the food?

Another worry is that the chemicals from the plastic may leach into the food when heated, since a study and some other research got people to suddenly start pitching their plastic containers in the trash. 

That may be so, but it isn't any more likely than with vacuum bags designed for sous vide cooking -- they are made out of the exact same kind of plastic. The Ziploc website, for example, says that all of its bags are BPA and dioxin-free, which are some of the chemicals that most people are afraid of when using plastic.

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Most zipper bags are safe to use for cooking in water baths.

Alina Bradford/CNET

To be on the safe side, stay away from any brand name or generic plastic baggie made with polyvinyl chloride (PVC). A little research on the company's website should tell you what the bags are made of. High-density polyethylene, low-density polyethylene and polypropylene are the safest plastics to cook with. Thankfully, that's what Ziploc bags and most other zippered bags are made of.

Will they melt?

Well, yeah, if you subject them to high temperatures. Polyethylene plastic, which is typically used to make these bags, will start to soften at about 195 degrees Fahrenheit (90.6 degrees Celsius). If you put them in boiling water (around 212 degrees F or 100 degrees C), they will melt. Most sous vide cooking temperatures are below 190 degrees F (87.8 degrees C), so you shouldn't need to worry about melting.

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First published Nov. 20, 2015 and has been updated.
Update April 6, 2018 at 2:26 p.m. PT: Refreshed article with photos and video.

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