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Freezer bag cooking refers to cooking by boiling water in a pot, add the boiling water to a zip-lock type freezer bag filled with the meal, placing the filled bag in an insulating cozy, and letting everything soak/heat/cook until edible. I have read varying views on the safety of the method concerning adding boiling water to the plastic bag and chemicals leeching into the food. Andrew Skurka says:

Do you think it’s safe to heat food in a freezer bag? Ziplok does, based on the standards set by the EPA for food-grade plastics. I’m not concerned with what they know, but what they don’t know yet (a la BPA), and I’d rather not chance it when there’s a reasonable alternative.

while TrailCooking.com says about the safety of freezer bag cooking:

Our personal opinion is yes, but you really should do the research yourself and make your own informed decision. We have provided some discussion points and links below to help you make that decision.

Has anyone done a proper chemical analysis or study to determine if it is safe?

  • 1
    That's a tricky one to answer, many studies have been done on polyethylene for heating food and the opinions are mixed. But it is not an immediate health threat. Meaning any adverse health reactions are thought to be much later and cumulative rather than after one meal. See also sous-vide cooking which is thought to be safe because of its lower temperatures. Boiling water tends to make polyethylene reach its softening point, which has been shown to have an increase of leached chemicals. Whether or not those chemicals are bad for you is a hot debate.. but they are chemicals.. – Nate W Feb 13 '18 at 23:25
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    "I’m ... concerned ... what they don’t know yet" Since you can't know all the things you don't know, the only possible answer here is to not do it. – Olin Lathrop Feb 14 '18 at 12:08
  • @OlinLathrop the Skurka approach seems overly cautious. It seems like there might things chemists/biologist do know that could tell us it is bad. Alternatively, they might be able to identify unexplored areas where dangers may be lurking. They may also be able to say that it has been tested every which way and no reasonable person should be concerned. – StrongBad Feb 14 '18 at 19:42
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TLDR: It looks like the bigger risk is spilling the boiling water onto yourself.

Here is what Ziplok has to say about their products,

That’s good news all around.Ziploc® brand containers are made from polypropylene and can be recycled in a limited (but growing number) of communities.

...

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.

...

A few years back, concerns were raised about the alleged dangers of using plastics in microwaves. The presumption argued that a combination of fat, high heat and plastic releases dioxin into food and ultimately into the cells of the body, which would then increase the risk of producing cancerous cells. After we researched these claims, it became clear that the information was misleading and unnecessarily alarming.

Source

According to National Geographic the is used in,

  • deli soups, syrup, yogurt and margarine containers
  • disposable diapers
  • outdoor carpet
  • house wrap
  • clouded plastic containers,e.g. baby bottles, straws

and there are

No known health issues

Source

From a SAFETY DATA SHEET Polypropylene (PP)

Ingestion:

No known significant effects or hazards

...

Melting Point | 150-170 °C (DSC)

Decomposition temperature | >300°C (>572°F)

...

Chemical stability:

This product is a stable thermoplastic with no chemical reactivity under normal handling and storage conditions.

Possibility of hazardous reactions:

Under normal conditions of storage and use, hazardous reactions will not occur.

Conditions to avoid:

Strong oxidation agents, avoid temperatures above 300 degree C (570 F).

This article says that polypropylene is considered less risky for leaching compared to other types of plastic..

There appears to be even less concern – which has translated into fewer studies – regarding leaching of toxins from polypropylene (recycle code 5), the other plastic dinnerware workhorse. Polypropylene bowls and plates are also considered safe to use in the microwave.

What about BPA and phthalates?

What we do know though is that neither polypropylene nor melamine contain two of the toxins that have raised concern in recent years: bisphenol A (BPA) and phthalates.

Other notes I found,

All of the plastic food containers that we examined in our kitchen were branded with the number 5, which means they’re made of PP, or polypropylene. That’s a cloudy plastic generally considered to be food safe.

Source

Not so, says vom Saal, who notes that there are plenty of other materials, such as polyethylene and polypropylene plastics, that would be fine substitutes in at least some applications. "There are a whole variety of different kinds of plastic materials and glass," he says. "They are all more stable than polycarbonate."

Source

I also found a study where the microwaved water in plastic containers and tested for leakage.

The Effect of Microwave Radiation on Polypropylene Used in Food Containers

The question of whether or not any potentially hazardous organic compounds were being introduced into food by the plastic itself was also addressed. Although there were not any specific answers given to these questions, the quality of the plastics commercially available were evaluated. The results proved that the plastics used in everyday food containers are of good quality and do not leach enough hazardous material to be in anyway harmful.

...

The results indicated support of the original hypothesis. No evidence was found of any harmful chemicals leaching into food from the plastic dishware.

  • "...and do not leach enough hazardous material to be in anyway harmful" key qualifying term – cr0 Feb 15 '18 at 19:09
  • seems that statements about bag safety at room temperature (most of your answer) aren't relevant to the question. – johny why Sep 21 at 4:40

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