Who doesn’t love the smell of bread baking? And you can’t have bread without flour, can you? Flour has been one of humanity’s staple sources of nutrition through the ages with our tradition of bread making going back, at least, thousands of years. But has our desire for bread left us open to the risk of fire and flame? Is flour something we should be more cautious about using?
Flour is flammable and can catch fire or even explode in some situations. This is mainly due to the high surface area as a powder, which makes for a high air to fuel ratio.
Flour has a serious explosion hazard when the dust is in the air and it’s very important to be cautious. Here’s what you need to know.
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Also read: What Makes Something Flammable?
What Is Flour?
Flour is the catch-all name for powders that are created by grinding down roots, beans, nuts, seeds, and grains.
Flours can be employed in the manufacture of many different food items and in Western culture, the most common flours used are cereal flours (and, in particular, wheat flour) for the production of bread.
In Mesoamerican cultures, corn flour has been the preferred flour and in parts of Europe, rye flour was the staple ingredient of bread.
You can make flour from either a mixture of the bran, germ, and endosperm of a cereal which is what we call whole-grain flour.
It can also be produced just from the endosperm and in that case, it’s called refined flour.
Another similar product to flour is “meal”. It is made using the same process but with a coarser level of grind that produces a bigger end particle than that of flour.
There is no official definition of what makes flour vs what makes a meal. Thus, cornflour and cornmeal might be very similar when purchased off the shelf or they might be very different.
The name “flour” comes from “flower” and is derived from the French word, “fleur”.
While this literally means “flower” it also refers to the “finest ingredient in a meal” and thus flour represents the “finest” part of the crop used to make it, with the coarse and indigestible matter being removed during the milling of the flour.
How Is It Used?
Flours of all types are used in cooking.
Many flours result in bread (whether leavened or unleavened), but others may be turned into cakes and desserts in Western culture.
But other flours may be turned to all sorts of uses, for example, potato flour (which is not potato starch) is the basis of “instant mash” or “smash”.
Hemp flour, on the other hand, can be used as a green dye for other flours or it can be used in its own right to make products from.
And so on…
Is Flour Highly Flammable?
If flour were kept in a single solid piece, it would not be flammable, in fact, it’s unlikely that in most cases it would burn very well at all.
However, it is not kept as a single solid piece, it is fine dust, and dust and powders tend to be very flammable, even if the solid product is not.
This is because creating dust dramatically increases the surface area of the product when compared to its overall volume.
This allows it to absorb far more heat and far more quickly than the solid product could and thus, it will burn far more easily than the solid would.
This means that flours are, generally, highly flammable and need to be stored very carefully and, in particular, not allowed to congregate in the air.
Also read: Is Dust Flammable? When To Worry…
Is Flour Explosive?
Flour is highly flammable but if it sits in the air, it is also an explosive risk.
That’s because once the flour catches fire, it produces enough heat to set the next piece of flour on fire and the next and the next, the whole reaction can self-propagate very quickly, indeed and that can lead to a serious explosion.
If you have any doubts that flour will actually explode, watch this:
Why Did The Flour Explode In Equalizer 2?
This is a popular question among movie fans, but it’s not made explicitly clear that the scene in which dust particles are blown by industrial fans and then set on fire, actually does use flour – it could also be sugar.
However, as we’ve already seen it doesn’t matter too much if it’s flour or sugar, dust in the air is highly flammable and the Equalizer 2 uses this knowledge to drive towards its violent conclusion.
Can Flour Mills Explode?
Yes, one of the earliest records of this in the United States, took place in 1878 at the Washburn A Mill.
It killed 18 people and destroyed a very large area of land and buildings.
While no flour explosion has been as serious in the United States since dust explosions still take place fairly regularly across a range of industries.
For example, in Georgia in 2014, a sugar mill exploded killing 14 and injuring many more.
The milling industry works very hard to reduce the number of dust particles in the air at any given time and the workforce is well-trained to spot fire hazards and deal with them but accidents are still a real risk due to the highly flammable qualities of dust.
This video talks more about how this can happen:
Does Flour Stop Fire?
As we’ve already established, flour is highly flammable and potentially explosive and it must never, ever be used to try and extinguish a grease fire.
If you’ve ever seen someone using a dusty substance to put out a small grease fire – that substance was probably baking soda (sodium bicarbonate) which does not burn, even in dust form, and can soak up the grease and thus, remove the fuel from the fire.
If you were to use flour instead of baking soda, you would make things much, much worse and potentially blow up the kitchen rather than saving it.
What Happens If You Smoke Flour?
Flour can be smoked, not in a cigarette mind you, but in an industrial process to help change the chemical properties of the flour to influence the kind of bread that it will make.
This isn’t something that you should attempt at home, as you’re likely to create large clouds of flammable dust, but it’s something that industrial bakeries and mills do on a fairly regular basis.
Does Flour Expire?
Yes, flour has a fairly long shelf life but after 3-8 months it will start to turn bad.
White flour tends to last the longest as it has less fat in it than other forms of flour.
If you’re worried about this, you can help to extend the life of your flour by sealing it in an airtight container, keeping it out of light, and either refrigerating or freezing it.
The expiration of flour has little effect on its flammability, mind you, unless the expired flour starts to clump and stick together, in which case – it becomes less flammable.
Flour doesn’t smell very much when it’s fresh, but when it goes bad it will often have a sour smell or even smell of must/mold.
In general, old flour is not harmful to human health but if there is mold present that can be toxic and it’s best to just throw out any flour that you’re not sure about.
Does Microwaving Flour Kill Bacteria?
There is currently no evidence that putting flour in a microwave will help to kill any bacteria or mold spores that is present in the flour.
This is also true for oven baking flour before using it.
If you have any doubts about the way your flour might react when you eat it – it’s safest to dispose of it and buy some more.
While we don’t encourage unnecessary waste, we would note that it’s better than getting sick and flour is very inexpensive.