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This question is about the plastic "Oven Bags" used to roast various kinds of meat or poultry in. I have some of these made by Reynolds Co., and in the Cooking Guide that came along in the package, it says: "Add 1 TBSP flour to bag. Shake! This helps prevent bag from bursting." This was before you put the rest of the food into the bag. Well, it didn't burst, so I guess that means it worked, but they also had me cut six slits into the bag to let steam escape.

My question is how would the 1 TBSP flour prevent the bag from bursting, and why would it burst anyway, with six slits in it?

  • Can't answer and I was surprised about how adamantly the company insists on using flour. The oven bags available here in Germany don't mention flour at all in their instructions. And yes, the slits prevent bursting. Perhaps they want to thicken the juices into a kind of gravy? – Stephie Nov 24 '17 at 20:09
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See this 1972 NYT article from back when these bags were a recent invention and the explosion problem was still current news. https://www.nytimes.com/1972/04/08/archives/why-cooking-bags-explode.html

In recent years, news was made of the dangers of boiling water in the microwave in something like a Pyrex measuring cup, because water heated in that manner could potentially become superheated (hotter than the normal boiling point, but not bubbling, steaming, or visibly boiling) if the surface of the container is so smooth that "nucleation sites" don't form. It then sits there, hotter than boiling but looking still (as if it weren't boiling yet) -- until something disturbs the surface (like the next ingredient, or your hand jostling the cup), at which point it can violently and simultaneously boil, seeming to explode.

Apparently the same thing was thought to be happening in these cooking bags due to water getting trapped under a layer of grease from the meat, and the flour would help those nucleation sites to form (called "boiling chips" in the NYT article) and also bind with some of the fat and water to form a gravy instead of letting the water remain separated. I am not a scientist but I don't think I've said anything egregiously wrong.

Justin Wilson mentioned the explosion risk and the need to use flour in one of his cooking shows back in the day while demonstrating the bag, but didn't go into the science of it, just mentioned that the flour was needed and went on with the show. It's in an episode called "Cajun Meat and Potatoes".

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My hypothesis is that they believe (correct or not) that the flour will absorb excess moisture. Absorbing this moisture could prevent a build up of steam and the bag "blowing up", and perhaps they also think it could lead to crisper skin. I don't know how true this is, but it seems like a plausible hypothesis!

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