Are harmful chemicals leached from ordinary Ziploc bags when used for sous vide cooking?

Question

Sous vide cooking is a style of cooking where you seal meat in bags and soak it in water at a specific temperature for a very long time, sometimes days. Some worry that in this process, harmful chemicals can be leached from the bags.

In the Environmental Health Perspectives study, Yaniger et al. set out to determine the estrogenic activity of commonly used plastic consumer products.

They bought more than 500 plastic products at places like Wal-Mart, Whole Foods, Trader Joe’s, Target, and other major retailers. They selected from all categories of plastic, including tupperware containers, bags and wraps.

Then they cut the containers into pieces, put them into liquids that contain similar chemicals found in food and drinks, and subjected them to stresses that mimic normal use, like UV light (sunlight), microwaving, or moist heat (like boiling or dishwashing).

Their results showed that over 90 percent of the products leached estrogenic chemicals before they were even stressed, and after being stressed essentially all of the products showed estrogenic activity.

The chemical referred to in this article is BPA.

Should I worry that using Ziplocs for sous vide style cooking could cause harmful chemicals to leach into the meat? If chemicals do leach, do they do so at an amount that could cause damage?

Answer 1

Ziploc brand bags do not contain BPA, according to the manufacturer:

http://www.ziploc.com/Sustainability/Pages/Safety-and-Plastics.aspx

SC Johnson’s Ziploc® brand Bags and Containers are BPA free. Our products are extensively evaluated for toxicity and safety and comply with applicable quality and safety regulations.

Nor do they contain Dioxins:

After we researched these claims, it became clear that the information was misleading and unnecessarily alarming. Dioxins only form when chlorine is combined with extremely high temperatures (such as 1,500 degrees F). The most powerful kitchen microwave oven will never reach this temperature. Even if you reached 1500F (theoretically), all Ziploc® brand products are 100% dioxin-free.

Glad brand food storage bags also claim to be BPA-free:

http://www.glad.com/faq/

No. Glad food containers, wraps, storage bags and other food contact products are not made of phthalates or polycarbonate. Nor is Bisphenol A (BPA) used as a raw material in their production. For more information, read our official statement.

As that cooking style requires a vacuum-sealed plastic bag, you might be best served by sticking with one of these brand names, which have more to lose by containing toxins than a no-name store brand.