Cooking Sous Vide: Plastic Safety

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You know I love cooking sous vide.

Despite my hectic work schedule and parenting duties — not to mention daily food blogging! — I’m still able to whip up healthy, tasty, perfectly-cooked meals with minimal prep time, thanks in large part to my SousVide Supreme. It’s one of my go-to kitchen appliances, and I’ve developed a number of recipes that call for vacuum-sealing various proteins and dunking them in my temperature-controlled water bath.

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So naturally, I was alarmed to read Chris Kresser’s recent post about a new study that shows that most plastics — including many that are BPA-free — can leach out chemicals with estrogenic activity (EA). In the study, researchers tested over 500 plastic products available to consumers — including baby bottles, tupperware containers, sandwich bags and plastic wraps — and found that virtually all of them leached chemicals that “produce an increase in circulating estrogen, which in turn can cause problems such as early puberty in females, reduced sperm counts, altered function of the reproductive organs, obesity, increased rates of certain cancers and problems with infant and childhood development.” 

Yikes.

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But that’s not all. Chris is an avid sous vider, and has been using reusable plastic bags to seal his food for cooking — so he had a special note of warning for his fellow sous vide fans:

After reading this study, I’m feeling very uncomfortable about the idea of eating anything that comes out of a plastic bag that has been sitting in a hot water bath for several hours. This is a crushing blow, as I love cooking with the Sous Vide. But in light of the evidence that even BPA-free plastics bags leach chemicals with EA even without added stress like a hot water bath, I think erring on the side of caution is probably wise.

Double yikes.

This isn’t the first time I’ve heard of concerns about cooking foods at low temperatures that have been vacuum-sealed in plastic, but a number of food science gurus, including Harold McGee and Nathan Myhrvold, have given sous vide cooking a big thumbs-up — provided the proper materials are used for vacuum sealing. But none of ‘em had squarely addressed the EA-leaching issue that Chris raised.

My initial reaction? Crap. I can’t sous vide anymore. When it comes to Paleo science geekery, Chris is one of my favorite and most trusted resources, so when he talks, I listen. And in light of my mother-in-law’s recent bout with a form of estrogen-fueled breast cancer, Chris’s words of warning freaked me out.

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Still, given my ardor for sous vide cooking, I wasn’t about to give it up without exhausting all options. Once the initial shock of Chris’s post wore off, I sprang into action.

I did some serious digging, y’all. And luckily, I learned that there are some bags on the market that are indeed safe for sous vide purposes, and pose no problems from a BPA or EA perspective. The key is to stick with vacuum bags that are free of BPA, phthalates, and other plasticizers. It’s the plasticizers — chemical additives like phthalates that increase the pliability and fluidity of the plastic — that contain EA. 

I was able to confirm, for example, that Jarden’s FoodSaver bags are made from polyethylene glycol and nylon, and don’t contain BPA, phthalates, or other plasticizers with EA-leaching additives.

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Last year, Richard Nikoley shared this quote from an email list, noting that there is “absolutely zero danger” in cooking with FoodSaver bags:

The plastic that touches the food is made of 100% polyethylene, contains no plasticizers or estrogen-like compounds. The FoodSaver bags are 5 layers of polyethylene with an outer layer of nylon. While you might get BPA from your cans of coconut milk, there is simply no BPA that will get into your food from sous vide. 

The temperatures of sous vide are also low (polyethylene doesn’t begin softening until 195F), although I would imagine that a very small amount of polyethylene would still make it onto the surface of your food through diffusion. Polyethylene, however, is considered biologically inert, and scientists have been unable to detect any toxicity in animal tests (unlike BPA). It passes the Ames test and other studies of damage to DNA, and doesn’t have a similarity to estrogen. 

At this point, I’m unaware of any evidence at all that polyethylene poses any harm. As always, it’s up to you, but for me the taste and health benefits (less AGE production, nutrient loss, and protein degradation, and more retention of fatty acids) that sous vide provides far outweighs what seems to me to be an almost arbitrary possibility that it will harm me.

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I also reached out to Dr. Mary Dan Eades — the mother of the SousVide Supreme herself! — for her take on the EA issue. She, too, pointed out that the estrogenic additives in plastic “generally comes from the various phthalates and BPA” — neither of which are contained in the bags made and sold by her company. Dr. Eades continued:

[O]ur quality assurance testing on the plastics used in our cooking pouches involves stressing for 4 hours at boiling (which is never the cooking temperature in sous vide anyway) in migration studies using alcohol, olive oil, and distilled water in the pouches to simulate different types of foods that would be cooked. The results were that plastic components were not found to migrate into the food simulants even under stressed conditions.

Long story short: Both the SousVide Supreme pouches and the FoodSaver bags are perfect for quick, airtight vacuum-sealing, and it looks like both are also free of BPA- and EA-leaching issues. These pouches should be fine for sous viders who are concerned about minimizing prep time while maximizing food safety.

[UPDATED 1:30pm PST - Hold the presses! Stuart Yaniger, one of the researchers who published the study referenced above and a Vice President of R&D at PlastiPure, a company that certifies products as EA-free and thus “PlastiPure-Safe”, has commented below to offer an opposing viewpoint. According to Yaniger, EA can lurk in other additives as well, and thus no plastic or silicone products are truly safe “unless a manufacturer has developed the product specifically to be free of EA” (for example, PlastiPure-certified products). Please see his comment and my response below for more details.]

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But what if — like Chris Kresser — you’re reluctant to purchase single-use vacuum pouches for sous vide purposes because of the environmental waste? As Chris put it, even if the plastic doesn’t end up hurting you, it all “ends up in a big floating island in the middle of the ocean somewhere.” Other folks have also written to tell me that they consider it incredibly wasteful and eco-unfriendly (not to mention expensive!) to use single-use vacuum bags or pouches for sous vide cooking. 

Well, I think we’ve found a solution that addresses both the EA-leaching risks AND the environmental concerns.

The answer? Food-grade silicone bags.

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Fitbomb hit upon this solution and chatted with one of his workout buddies — Jackie Linder, the founder/CEO of LunchBots — about the possibility of using silicone bags for sous vide purposes. She, in turn, suggested that we check out Lekue’s reusable silicone food pouches (available on Amazon for $20 per bag). We looked into ‘em, and ordered some to try in our SousVide Supreme.

[UPDATE 9:55am PST - It looks like the clear Lekue bags are selling like hotcakes now! They’re temporarily out of stock at Amazon, but the green, blue, and red ones are still available.]

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The verdict?

It works! (Well, with the one recipe we’ve tried so far, anyway!)

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Yes, the silicone bags are thicker than typical vacuum-seal food pouches, so some recipes may require a bit of experimentation when it comes to cooking times. They’re not huge, so big or oddly-shaped foods may not fit. Additionally, manually squeezing/displacing all the air out of the silicone bags can prove a bit tricky and take some extra work. But these Lekue bags are dishwasher-safe, re-usable, and relatively inexpensive. So all you hippies out there can start sous viding guiltlessly!

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Am I saying you should ignore what Chris Kresser has to say about EA leaching from most plastics? Not at all. He cites valid concerns about using plastic food and beverage containers and utensils, and since reading what he had to say, I’ve cleared my cupboards of all of our plastic bottles, cups and bowls, and replaced them with stuff from LunchBots and other makers of stainless steel and glass dinnerware. Yes, I realize that statistically, the health risks of using a plastic plate is nowhere near the risk of, say, getting into a car and driving to work — but there’s no reason to keep feeding my kids out of plastic receptacles when I could just as easily serve ‘em meals using glass or stainless steel containers.

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Likewise, if you’re vacuum-sealing your food with plastic bags containing BPA and/or plasticizers like phthalates, you should switch to something else pronto. As I’ve described above, there are options out there that are perfectly safe for cooking sous vide.

One final note: In case you’re wondering, I’m not a paid shill for any of these products. Sure, I’ve gushed about my SousVide Supreme and guest-blogged for them in the past (for free), and I’ve purchased reams of FoodSaver bags from Costco and Lekue silicone bags from Amazon. But cross my heart and hope to die, stick a needle in my eye: I wasn’t asked by anyone to hype ‘em up in response to Chris’s post. If you end up buying any of these products from my Amazon shop, I get a small percentage commission, but that’s it. 

I’ve spent a TON of my own hard-earned dinero to buy all my kitchen tools myself (including my SousVide Supreme and various types of bags). I just love sous vide cooking, and want to use BPA- and EA-free pouches that are safe for my husband and kids.

After all, I’m not trying to kill them — even when they piss me off.