Careful with what dry ice you get, not all of it is pure carbon dioxide and may have contaminants in it that you wouldn’t want in your food.
If it didn’t displace the O2, then the total pressure would rise and either pop the lid off or rupture the container.
Atmospheric gasses would be displaced away from the brick of dry ice; this is why you place the brick at the bottom of the container, as far from the opening as possible, so that atmospheric gases get displaced toward the opening.
If a pile of flour weren’t porous/permeable, you might have a problem. But it is, so everything will be fine.
For anyone interested in avoiding the tedium of the USDA defect level handbook, you might prefer this short pop-quiz.
No, but I’m pretty sure that there are also a higher percentage of bug bits in a rural Indian diet than in the highly processed American diet. (Probably. I hope.)
Bolding mine. This sounds like it would work. I’ve had some experience with dry ice, and found that it’s generally found it impossible to contain the gas (CO2) build-up. If the box is closed too soon, what happens is…
You might be amazed at how much pressure can be generated otherwise.
I’ve seen somewhere a recommendation to store flour in a freezer for a while (a couple of days?) to kill any eggs that might be in it. Then it can safely be stored at room temperature without any danger of bugs hatching. I think that would be easier than the dry ice idea.
Aaah! Get 'em off! Get 'em ooooffff! Shakes around wildly
Dopers,
Your amazingly speedy and informed response has inspired me. That along with the realization that I can get dry ice at the grocery store near my house.
I have four airtight-or-nearly-so plastic food containers, about one quart each. Into each container, I have placed two cups of all-purpose flour. Into two of the containers (“the experiment”) I have placed a small (maybe 2 tablespoons) amount of dry ice (solid CO2, -109 deg F, “Penguin” brand), under the flour (the ice went in first). The other two are in all ways similar, but without dry ice (“the control”).
Preliminary observations:
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Let the gases vent. I was “burping” and re-sealing the containers to watch the tops bubble, took a comfort break, and was surprised to hear a “pop” as one of the lids went flying. Fortunately, no mess.
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Dry ice is absurdly cheap ($1.09/pound, and thats in a grocery store, so you know I’m paying a premium). I spent $0.15 on a few chips of dry ice. So this might actually be, well, not practical, but economically logical.
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Dry ice sublimates while you wait, so a long line at the grocery store means I saved a few pennies. Ha!
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Weather-wise, it is June in Washington, D.C. Hot (90F+) & humid. Occasional scattered T-storms.
I will keep you posted on the outcome.
Yes, the quote is xkcd.
Biology is not my strong suit, but do bugs (the ones we don’t like in our flour, that is) require oxygen to survive? Are we only assuming that the lack of it is detrimental to their health (because it is to ours) or is that a sure thing?
From April of this year:
Scientists have found the first multicellular animals that apparently live entirely without oxygen.
Lack of oxygen’ll kill any insect found in flour. However, carbon dioxide is not only not oxygen, but it’s flat out toxic:
The gas probably messes with an insect’s internal pH.
I keep my flour in the freezer, in a closed plastic box. But I use only whole wheat flour, so I have to.
Why? Why for whole wheat flour, specifically?
Or you can have fun doing the math. The molecular weight of CO2 is (approximately) 44 grams. So one mole of dry ice is 44 grams, and when it all sublimates it will expand to 22.4 L (volume of an ideal gas at standard temperature and pressure.) It’s then a simple equation to figure out just how many atmospheres of pressure you’ll get in your sealed box as a result. This is left as an exercise for the reader.
I have to say, now I wonder how much pressure your standard Tupperware container can take before the seal at the lid fails.
How about doing it the other way? Put it in a container equipped with a one-way valve and pull a reasonable vacuum. Ideally you’d keep it under a constant pull, since otherwise the box would probably leak and eventually repressurize. This, of course, will be noisy, suck a lot of power, and ideally you’d need to keep some sort of cold trap on it.
Whole wheat flour contains more fat than white flour, and that fat can go rancid and make it taste funky. Freezing your whole wheat flour makes the rancidity process slow, so you have longer to use it before funkification.
Oh, come on. You can’t leave us all wondering. Get in the kitchen and start experimenting, Mr. Wizard! Post pics. 
But wasn’t it toxic because it displaces oxygen, both in the air and in blood (once the ratio of CO2 to O2 is high enough)? It drowns you. CO and CN- have the same mechanism but at much, much lower ratios (they “stick” to blood a lot better than CO2); saying that “CO2 is toxic” is more akin to saying that “water is toxic” than to saying that “CO is toxic”. Dihydrogen monoxide kills people every year but outside of an MSDS you won’t usually call it toxic.
Whole wheat contains the wheat germ, which is refined out of white flour, along with the wheat bran. Wheat germ gets rancid quickly and that’s the reason most flours are refined. I also have a jar of wheat germ, which I keep refrigerated. Toasted wheat germ is a better option if time is the main factor.
That’s what I said. It’s specifically the oil (fat) in the germ that goes rancid.
I knew I heard that somewhere before.
Well, I needed the containers, and we were cleaning the kitchen, so here are the results after 2+ months (28 Jun - 04 Sept)…
No bugs in any of the four containers (2 experiment, 2 control).
So no conclusive results, either way.