Exploding custard

How explosive is custard powder?
31 March 2020

Interview with 

Dave Ansell, Sciansell; Giles Yeo, Cambridge University


this is a lit match


Science demo superstar Dave Ansell shows Adam Murphy what happens when you set fire to cornflour...

Adam - Now, as we said, we promised you demos and it wouldn't be a proper Naked Scientists show without them. So I'd like to introduce science demo superstar and former naked scientist, who's going to put the boom in this show. Please give a round of applause for Dave Ansell. So Dave, we're talking about food and we're talking about calories. So what kind of food calorie -related demos have you got for us?

Dave - I thought we'd look at releasing those calories in a slightly different way.

Adam - Right, so not eating.

Dave - No, not quite the way you do in your body, but as a physicist in a very similar way. So your body basically, as far as I'm concerned, you're taking in energy, you react that with some oxygen and it does something useful with it.

Adam - So what does that look like?

Dave - So here I have a pot with vegetable oil in it and a string coming out the top, just like a candlewick. If I light it, we have a really exciting demo!

Adam - It's a small candle flame.

Dave - Indeed. So this is going to sit there maybe for a couple of hours and burn gently. It's the way a lot of light was produced in the ancient world.

Adam - But is there anything else we can do with food?

Dave - Well this is releasing quite a lot of energy over a very long period, so it's not that exciting. What I thought we'd try and do is increase the speed at which we release that energy. So in order to burn something quickly, you need to be able to get the oxygen to more of it at once. Yeah. So what you do that is by using very, very small particles, like a powder, like custard powder. So the particles in custard powder, they're basically starch so cornflour and they're about one micron across, about 1000th of a millimeter across. So if you imagine the surface area of all of these tiny tiny particles, it's absolutely immense. And so basically if you can get the oxygen to custom powder, it can burn almost everywhere at once.

Adam - And - he asks dramatically - what might that look like?

Dave - First you need a device for doing this. It looks a little bit like a pipe. I'll put a little bit of custard powder in this. There's a long tube attached to that and we need a source of ignition, so I'll light this blow torch.

Adam - I'm a coward so I'm stealing your goggles.

Dave - And then if I blow through this tube, the air will swirl in here. Mix the air in really nicely with the cornflower -

Adam - You're kneeling down in front of it, about to blow through the pipe -

Dave - [whoosh] We get a very cool little fireball! I mean at this scale, that's kind of pretty. If you're running a flour mill, it's a whole other kettle of fish. If, say you have a big bag of flour, it drops down from the top of your flour mill. It bursts, it fills the whole flour mill with flour, which is the same stuff as corn flour basically, all carbohydrates. There's a flame in the corner, bang! Hundreds and hundreds of windmills and other forms of mills blew up through that very reason. They were incredibly paranoid about not having flames in mills, for good reason.

Adam - And that's certainly not what I want to happen while I'm having cake anyway. Now Giles, maybe I'm in the minority here, but I feel like when I put a donut into myself, it doesn't burn up in a big fireball. So what's different about what my body's doing to turn food into energy?

Giles - It's actually, it's very interesting because when you eat food, we think about it in calories, right? We think, oh, this is a hundred calories. This is 200 calories. And what's interesting is a calorie is the amount of energy it takes to raise one liter of water, one degree Celsius. At sea level, that's a calorie. Okay? But if you think about it then how many calories do you need to boil one liter of water? The answer is a hundred calories. A chocolate bar only has 230 calories and we're not boiling. The way that our body actually does it is we then take that food and transform it into into energy, but in stepwise forms. So if we take in fat and sugar and protein, we actually absorb it. It then goes through what we call intermediary metabolism, which means that the individual glucose particles, amino acids and fatty acid particles then produce ATP, ok, which is our little units of energy. And each of these then gives a little puff of energy every time they break apart, to then be able to move certain things and we actually recycle in our body our entire body weight in ATP - these little things - every single day - in order to function.

Chris - Quick question for you. Where's Sue, Sue Taylor?

Sue - Question about Benecol, does it actually work? Benecol and things like Proactive margarine, do they actually work?

Giles - Other spreads are available, but these come with a manufacturer's sign that says "helps lower cholesterol", help being the critical word and "lower cholesterol". Now I'm not entirely sure of what the active ingredient is supposed to be in these things, but as far as I understand there is a modest effect in some people, okay. And this is the critical thing. Because not everybody's cholesterol levels are going to be sensitive to diet. To my view rather than eating a lot of spread, which is fine if you dig spread I guess, I think if you actually reduce your saturated fats and ate more unsaturated fats such as from olive oil and maybe from ground nuts, that's probably going to be more effective on lowering your cholesterol levels. If your cholesterol levels are sensitive to diet.

Chris - Hands up in the room if you prefer butter to margarine......It's about half and half. Sue, you had another question.

Sue - Is butter better?

Giles - Once again, it does depend who you are. There are going to be some people who can literally take a stick of butter and eat it and their cholesterol levels will not budge. Okay. And those are, you can call them lucky people, they may get fat. That's a very different scenario, a different problem. But from the heart perspective, but they're going to be some people, and I know I'm one of them. My cholesterol levels teeter on a little bit high. I know they're sensitive because when I went on a vegan diet, cut out my saturated fats, my cholesterol levels plummeted. So if I ate a stick of butter, I probably keel over from a coronary. So once again, I think it is very, very important when you begin to ask questions about food, that it doesn't work the same in every single person. So it depends is the answer.


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