Is it Safe to Sous Vide in Any Plastic Bag?
The first time I saw boil-in-a-bag rice, I was horrified — and also a little dumbfounded. I couldn't understand how the plastic wouldn't melt when boiled. And even if it didn't melt, wouldn't it leech chemicals into my food?
Years later in culinary school, we learned to sous vide — essentially, to cook (but not boil) food in plastic bags. Sous vide is a very old cooking technique that literally translates to "under vacuum." The idea is that when you put food in a vacuum-sealed plastic bag and submerge it in water heated to a specific temperature (generally under 190 degrees Fahrenheit), it cooks incredibly gently and evenly, and retains more moisture. Chefs love that they can sous vide well in advance, and finish the dish right before serving: sous vide food is nearly impossible to overcook.
Okay, I'm sold. It's the best ever stress-free way to cook for a party. But will any old plastic bag do or do we need very special, heavy duty bags to prevent the plastic's chemicals from transferring to our food?
To find out, I turned to one of my favorite food safety experts, Dr. Don Schaffner. I know the good doctor from Rutgers — who has served on the US National Academy of Sciences, World Health Organization, and the Food and Agriculture Organization (FAO) — will always err on the side of being more protective of our health. He's a very careful guy. Here's what he had to say.
"There are risks for cooking sous vide, but I don't consider using zip lock bags high on the list of what those risks are." From a microbiological perspective, said Dr. Schaffner, the key to safety of sous vide cooked food is getting the cooking time and temperature right.
Now, Dr. Schaffner wouldn't approve of just any old plastic bag. Inexpensive, flimsy zip top bags may contain BPA and phthalates, substances which act as "hormone disrupters" that can transfer to our food when heated in the microwave. They may also contain polyvinyl chloride (PVC) which can leech into foods — especially fatty foods like cheese, and meats. (That's why we were warned several years ago to not rest plastic wrap directly on food when microwaving.)
Look for bags made from high-density or low-density polyethylene and/or polypropylene. They can't be boiled, but are food safe (and won't melt) up to about 195F. (You wouldn't sous vide at that high a temperature anyway.) Ziplock and Glad brand bags are made from polyethylene plastic, and are free of BPAs and dioxins. A good rule of thumb is that when a bag is rated as microwave safe (which requires FDA approval) you can use it for sous vide. Even Dr. Schaffner agrees.