From the blog March 12, 2013 Nathan

Is It Safe to Cook with Plastic?

Since writing Modernist Cuisine and Modernist Cuisine at Home, we’ve been asked many times to comment on the safety of cooking in plastic bags. Many of our sous vide recipes, from our Sous Vide Salmon and Rare Beef Jus to our Cranberry Consommé and Scrambled Egg Foam, require vacuum-sealing or using a zip-top bag. Similarly, many of our recipes that utilize microwaves, such as our Microwaved Tilapia, Eggplant Parmesan, and Microwave-Fried Herbs, require plastic wrap.

According to the latest research, the safest plastics for use with food are high-density polyethylene, low-density polyethylene, and polypropylene. Virtually all sous vide bags are made from these plastics, as are most brand-name food storage bags and plastic wraps such as Saran wrap. Polyethylene is widely used in containers for biology and chemistry labs, and it has been studied extensively. It is safe.

Less expensive, bulk plastic wraps sold to the catering trade are not as safe, however. These products are commonly made from polyvinyl chloride (PVC), which can contain harmful plasticizers that have been shown to leach into fatty foods such as cheese, meat, and fish. Legitimate concerns exist about food exposed to these plastics at high temperatures. Polyethylene-based plastic wraps are available at only slightly higher costs and do not raise such concerns. An easy way to spot the difference is to check that your cling wraps or plastic bags are rated microwave-safe. Bags and wraps made form polyethylene are generally microwave-safe, whereas those that contain polyvinyl chloride plastics generally are not.

Many professional kitchens use clear, rigid, plastic storage containers that are made from polycarbonate. While they are currently approved for food use, these plastics also may be a cause for concern because they contain bisphenol A (BPA), a chemical that can disrupt hormone activity and leach into foods and beverages. Cracks and crazing due to wear and tear increase the rate at which BPA leaches out of polycarbonates.

The bottom line is that bags made expressly for cooking sous vide are perfectly safe—as are oven bags, popular brands of zip-top bags, and stretchy plastics such as Saran wrap. If you remain hesitant to try cooking sous vide due to concerns over plastic, you can always use canning jars instead, but beware that cooking times will be longer.

—Adapted from Modernist Cuisine and Modernist Cuisine at Home

Discussion

  1. Hatton W. Sumner March 12, 2013 Reply

    Nathan,
    If you were cooking something that required 1 hour @ 140?F in a plastic bag, how long would it take in a Mason jar preheated to that temperature?
    Hatton

  2. Justin March 12, 2013 Reply

    Nathan,
    What about the claims of leaching EA into the bags.

    This blog post has a solid summary of the issue, and a recent study found many BPA free bags still leach chemicals with estrogenic activity (EA). I won’t dive into why this is problematic but was curious if you have seen this study.

    study
    http://www.ncbi.nlm.nih.gov/pmc/?term=10.1289/ehp.1003220

    blog post.
    http://nomnompaleo.com/post/12463202060/cooking-sous-vide-plastic-safety

    • Larissa Zhou March 19, 2013 Reply

      @Justin –
      The paper raises some important questions. With regards to sous vide cooking, while the study did find that a significant percentage of HDPE products contained detectable levels of EA, the stress (>100 C autoclave, repeated microwave exposure, etc) exposed to these products were very different from the type of stress occurring during sous-vide cooking. This study shows that we are learning more and more about the chemicals that surround us, though it does not answer questions such as the health effects of EA on humans, and if there are indeed negative effects, the minimum dosage for detection. For now, as nom nom paleo concludes as well, bags made specifically for sous vide are your best bet.

      Larissa
      Research scientist at Modernist Cuisine

  3. Jonathan March 16, 2013 Reply

    there’s a lot of discussion about plasticizers here.

    Are there concerns about the release and binding agents used in bag manufacture?

    • Larissa Zhou March 19, 2013 Reply

      Are there certain ones that you have in mind?

      Larissa

      • Jonathan March 24, 2013 Reply

        Hi Larissa,

        This is where my knowledge gets limited, unfortunately. I dug into this a bit and ran smack into the end of the internet.

        I would assume the most useful information would be about the processing agents used in producing Ziploc brand freezer and ‘sous vide’ bags, as those are the bags most of us in America use.

        Sorry to be inspecific, is this enough to clarify?

        Thanks.
        Jonathan

  4. ChuckMD April 13, 2013 Reply

    A widely used appliance for vacuum sealing of foods, one of wich I own, is FoodSaver (TM). Are FoodSaver brand bags suitable for sous vide cooking?

    • Judy April 19, 2013 Reply

      Yes, we use them for cooking sous vide all the time.

  5. Yann June 24, 2014 Reply

    According to the Pacific Northwest Pollution Prevention Resource Center, no studies were found in the literature evaluating migration of chemical additives from plastics in simulated Sous Vide conditions. And manufacturers have been unwilling to disclose the full formulations and additives. Source: http://goo.gl/yZRrw7

    So, I am opinion, whether “bags made expressly for cooking sous vide are perfectly safe” is still an open question.

  6. Larissa Zhou March 19, 2013 Reply

    @Raf – Heating can cause the plastic to break down and increase the speed of diffusion of the molecules into the surroundings. There are now BPA-free blender pitchers available (from KitchenAid, for example). However, the temperature of caramelized carrot soup and the duration of blending is much lower and shorter than the circumstances of the experiments that raised the issue of the harmfulness of BPA. For example, in the paper that Justin mentioned, samples were autoclaved at 134 C or heated in a microwave 10 times for 2 minutes each.
    For general ease of handling and if you are concerned about the temperature, you can wait for the soup to cool down a bit before blending.

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