Sous vide (pronounced “sue veed”) is a cooking method that chefs and restaurants have employed for a few decades. Recently, sous vide cooking has gained popularity with home cooks as well.
Sous vide means “under vacuum” in French. It involves sealing food in a plastic bag, submerging the bag in water and heating the water to a low, stable temperature, generally in the range of 140-160 degrees Fahrenheit. Early adopters of sous vide often created their own do-it-yourself sous vide cookers, but now machines are widely available both in stores and online.
WHY IS SOUS VIDE TRENDY?
What makes the sous vide method so popular is that submerging the food in water makes it possible to reduce the cooking temperature substantially. Instead of cooking something at 300 to 400 degrees, sous vide allows for cooking at 160 degrees. Moreover, cooks can hold food at this temperature for extended periods of time without overcooking or otherwise damaging the food. With most other cooking techniques, cooks have a narrow time frame to get a dish just right—neither under- nor overcooked. Sous vide extends that window almost indefinitely.
A restaurant or chef cannot know exactly who will order which dish when. With the sous vide technique, they can prepare a wide array of dishes ahead of time, pulling them when finally needed. This allows chefs to prep dishes much earlier in the day, which is a boon given the busy nature of modern restaurants. The same also goes for busy families. Many people who eat traditional foods have embraced sous vide because of the convenience factor.
SOUS VIDE IS SAFE…OR IS IT?
Because of the extended time window for sous vide cooking, food is in contact with plastic under temperature for much longer than many people realize. Is the convenience of sous vide matched by consumer safety?
As I wrote a few years ago in Wise Traditions, the safety of plastics has become a hotly contested and, at best, unclear issue, especially for so-called BPA-free plastics.1 BPA (bisphenol-A) is an additive that improves the clarity and toughness of the plastics to which it is added. Problematically, BPA displays estrogen-mimicking and hormone-disrupting properties. Public outcry over BPA-related health concerns caused companies to adopt “BPA-free” alternatives.
Many sous vide proponents point to these changes as being sufficient to ensure sous vide safety. These individuals downplay or completely dismiss any concerns over the plastics used in this cooking method. For example, a food and technology company “on a mission to help people cook smarter” states: “Although we cannot predict what may be discovered in the future, we believe that given today’s knowledge, using high-quality bags and handling them properly minimizes the potential risks of cooking with plastic. The way we see it, risk is just part of life—every time we cross the street or get behind the wheel of a car, we’re accepting a certain amount of risk.”2
Another sous vide enthusiast similarly dismisses concerns about cooking with plastic: “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 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.”3
Unfortunately, the science does not support these sous vide advocates’ position. Instead, research shows an alarming set of concerns around plastics in general, and especially plastics used in food preparation. As I wrote previously, “BPA-free does not mean safe, nor free of, other similar or even more dangerous chemicals that act similarly or even worse than BPA and other estrogen mimickers.”1
This is confirmed in a toxicology study published in 2011 in Environmental Health Perspectives, which examined more than four hundred and fifty commercially available plastic products used to contain foodstuffs.4,5 The investigators found that almost all of the products sampled “leached chemicals having reliably detectable EA [estrogenic activity], including those advertised as BPA free. In some cases, BPA-free products released chemicals having more EA than BPA-containing products.”5 As these authors note, chemicals with estrogenic activity can cause numerous adverse health effects in “fetal and juvenile mammals,” “especially at low (picomolar to nanomolar) doses.”5
Thus, there is no basis for claiming that the plastics commonly used in sous vide cooking are safe for consumers. On the contrary, there is clear evidence that all types of plastic, when exposed to heat, leach various chemicals into any surrounding medium, including food.
BETTER OR SAFER OPTIONS?
When concerns over plastics and sous vide cooking first emerged, the response among wellness folks was mixed. Some sought to find safer alternatives, such as other types of plastics or silicone-based cooking bags.
Once a big proponent of sous vide cooking, Chris Kresser had this to say about the safety concerns raised in the Environmental Health Perspectives study:
Special note for Sous Vide users: 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.6
Interestingly, Dr. Stuart Yaniger, one of the authors of the Environmental Health Perspectives study, responded both to Chris Kresser’s post and to a post at another website (which argued for the safety of polyethylene bags or silicone bags for sous vide).7 Dr. Yaniger’s response (see comment in reference 7) was instructive:
I am one of the authors of the study on EA in plastics that you cited…as well as an avid amateur chef. These…statements from your post [that some plastics are safe for sous vide cooking, as long as they do not contain plasticizers] are categorically untrue. There are many additives to plastics, and especially to the types of polyethylenes used in bags, that have EA, not just plasticizers. There are antioxidants, slip agents, antiblocks, process lubricants, and antistats. Additionally, there are low levels of impurities such as catalyst residues which can have significant biological activity, despite low concentrations. Silicone is no relief—although silicones can be formulated to be free of leachable endocrine disruptors, most aren’t, including most medical grades.”
For Dr. Yaniger, the bottom line is this:
Unless a manufacturer has developed the product specifically to be free of EA and can provide valid test data to confirm this (not a generic ‛this passes FDA standards’—FDA allows the use of BPA!), consumers should assume that the plastic is likely leaching endocrine-disrupting chemicals.
Now, how much of a health hazard [are] estrogen mimics from plastics? That’s still debatable and there’s a lot of research going on to pin this down. But if you’re concerned about the health effects of BPA, switching to a different plastic just means you’re swapping one hazard for another. It’s a fixable problem, but industry won’t fix the problem until consumers demand that they do.
Wow! Again, what we clearly see is that there is no such thing as safe plastics or silicones when it comes to food preparation. Yaniger’s response matches what I wrote about in an article on silicone bakeware8 and in my previous article on BPA.1 Silicone, while touted as safe, shows incredible problems under normal use, with leaching and contamination into food.8
Unfortunately, many wellness bloggers continue to defend the use of silicone bags,9 because they have not come across information deeming silicone bags unsafe. Silicone bags, in fact, are even more troubling than silicone baking molds and other silicone cookware because of the various additives and other chemicals needed to manufacture such materials.10
The reason why so few manufactured items are safe has little to do with the main ingredients or agents in these products. The main ingredients, even if not natural, are generally inert and innocuous on their own. Instead, it is the immense array of “processing additives”11—lubricants, colorants, solvents and sundry other chemicals—used to make the final products that are the source of contamination. For example, researchers note that “disposable plasticware is used in life science laboratories worldwide,” and “although labeling of plastics as ‘sterile’ appears to offer researchers some assurance that products are free of bioactive contaminants, the presence [and leaching] of processing additives is unavoidable.”11 These additives have “potent effects on enzyme and receptor proteins.”11
Similarly, the reason silicone bakeware and bags are problematic is because of everything other than the silicon that goes into making the final product. Until manufacturers find safer alternatives to replace these currently necessary industrial additives, or develop new methods of production that do not require them, almost any plastic or silicone product is going to come with concerns over contamination caused during the manufacturing process.
First and foremost, strive to reduce your exposure to all types of plastics and unnatural materials in all types of products, but especially food products and food preparation, handling and storage. Avoid silicone bakeware and cooking utensils. Instead, use glassware, such as Pyrex and similar glass storage ware. Use high-quality metal water bottles instead of plastic bottles.
For canning and fermenting, go with the lovely and excellent quality Weck canning jars with glass lids. A number of companies now also make all sorts of gizmos and gadgets that work with traditional mason jars, turning them into drinking bottles, fermenting vessels and more.
For cooking, a crock pot or a modern pressure cooker offer convenience without the risks and plastic pollution created by sous vide cooking.
No amount of convenience is worth risking the health of your family, particularly its youngest members who are most susceptible to the wide variety of estrogenic and other chemicals found in modern products, especially silicones and plastics.
1. Moody J. Don’t get canned: prepare now for canning season. Wise Traditions 2014;15(1): 48-50.
2. ChefSteps. A complete guide to sous vide packaging—safety, sustainability, and sourcing.
3. CNET. Why Ziploc bags are perfectly safe for sous vide cooking. https://www.cnet.com/how-to/why-ziploc-bags-are-perfectly-okay-to-use-for-sous-vide-cooking/.
4. Hamilton J. Study: most plastics leach hormone-like chemicals. http://www.npr.org/2011/03/02/134196209/study-most-plastics-leach-hormone-like-chemicals.
5. Yang CZ, Yaniger SI, Jordan VC, Klein DJ, Bittner GD. Most plastic products release estrogenic chemicals: a potential health problem that can be solved. Environ Health Perspect 2011;119(7):989-996.
6. Kresser C. How plastic food containers could be making you fat, infertile and sick. https://chriskresser.com/how-plastic-food-containers-could-be-making-you-fat-infertile-andsick/.
7. Tam M. Cooking sous vide: plastic safety. http://nomnompaleo.com/post/12463202060/cooking-sous-vide-plastic-safety.
8. Moody J. Silicone molds for baking: when to use, when to lose. http://www.thehealthyhomeeconomist.com/silicone-molds-baking-safety/.
9. Wellness Mama. What is sous vide (& how to do it without plastic). https://wellnessmama.com/156270/sous-vide-without-plastic/.
10. Skjevrak I, Brede C, Steffensen IL, et al. Non-targeted multi-component analytical surveillance of plastic food contact materials: identification of substances not included in EU positive lists and their risk assessment. Food Addit Contam 2005;22(10): 1012-1022.
11. McDonald GR, Hudson AL, Dunn SMJ, et al. Bioactive contaminants leach from disposable laboratory plasticware. Science 2008;322: 917.
This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly magazine of the Weston A. Price Foundation, Fall 2017.