Since I am a medical, allow me to make one point very clear.
There are many types of plastic bags, various plastic categories then there are variations that result in a myriad of plastic types. There are many uses of plastics in cooking, including using plastics in the microwave.
If you’re looking to create plastic food packaging or Sous-Vide cooking, it’s essential that you understand which plastics are food-safe. Foods that are highly acidic or that contain alcohol or fats can leach plastic additives from the packaging or container into the food.
Food-safe plastic resins are those approved for contact with edibles by the US Food and Drug Administration (FDA) for determining how materials may be caused in contact with food products. They are known as food contact substances (FCS). The FDA defines food contact substances as “any substance that is intended for use as a component of materials used in manufacturing, packing, packaging, transporting, or holding food.”
Food-safe plastic resins are separated from food by a functional barrier, they are nonvolatile and do not react to liquids, acids in the food, or bases, & biologically inert if ingested.
There are various kinds of plastic bags, some are not food safe at all, some are food safe only at low temperatures, and some are food safe even at or above boiling. Sous-Vide should always be done in bags that are food safe up through boiling, just by security.
The food-safe plastics bags are food-grade high-density polyethylene, low-density polyethylene, and polypropylene. When food-safe plastic bags are mentioned "microwave-safe" or "boil-safe", you can cook Sous-Vide. Plastic freezer bags are not all "microwave-safe" or "boil-safe" or "Sous-Vide" certified, I mean they are not high temperature certified.
My personal preference for food-safe plastic (freezer & cooking) bags is for products made of called polyethylene - Low Density Polyethylene (LDPE). It is widely used in containers & plastic films for biology and chemistry labs, and it has been studied extensively. LDPE can hold your food products without leaching any harmful materials or allowing microorganisms to permeate, plus breaking down collagen in meats for fork tenderness, then it is safe & good.
But, do avoid very cheap plastic zip wraps when cooking. These are made of polyvinyl chloride (PVC), and heating them presents a huge risk of chemicals leaching into the food.
Bottom line :
- Food-safe plastics bags made expressly for cooking Sous-Vide (or mentioned "microwave-safe" or "boil-safe") FDA / FCS approved are safe, so far. But most plastics – including many that are BPA-free – can leach out chemicals with estrogenic activity then we must be aware that limited information exists indicating whether any of the resins or additives used in these food-safe plastic cooking bags, or their degradation products, migrate or do not migrate from the plastic into the food
during the 3 or 4 hours long process of cooking.
However, the temperatures of Sous Vide are also low (polyethylene doesn’t begin softening until 195F), then, in my own opinion, it is a positive result, most of the toted benefits come not from the vacuum sealing but the high precision water bath.
Just provide the proper materials & cook at the right temperature, there are just a few easy precautions to watch for !
- I would definitely avoid the use of biodegradable plastic bag in cooking for the reason they made with additives. Biodegradable plastic, which is also made from petrochemicals (around of 25% less fossil fuel than regular plastic), is manufactured differently, made from organic, renewable sources, such as vegetable oils, corn, grains etc.. Biodegradable plastics are plastics that can be broken down by microorganisms (bacteria or fungi) into water, carbon dioxide (CO2), light, heat, and some bio-material. In my own opinion, they may more or less degrade during cooking under the influence of long heat. Moreover & unfortunately the biodegradable plastics produce methane when decomposing.
- Microwave cooking : While food contact materials are not intended to alter food, they are not necessarily inert or biologically inactive. Given the vast number of chemicals that may be used in food contact materials, I don’t microwave plastic.
Interested in more info for plastic? For clarification about plastic certification standards please check out :
Plastic Codes Explained
A good website for Sous-Vide cooking tips :
No Danger in Sous Vide Plastic Bags | Dr Terry Simpson
I should like to take this opportunity to stating also that we must use only Certified Water Pipe (Certified for potable water delivery), Polyethylene made with approved silicon, to fill our fresh water tank even if we don't drink fresh water from the tank, to avoid virucidal & plastic chemical (I never use use garden hose) activity on skin (shower, bath). Certified fresh water hose is also resistant to ozone and U.V. over long time periods. Easy to do and doesn't take much effort, the addition of a 5 micron filter to the inlet of the water hose when filling fresh water tank is a critical factor as well, since bacteria love to grab on micro-particles found in water & multiply very rapidly as a biofilm in oxygen-rich environments like the tank.