How does food give us energy?

WARNING: Jelly babies and gingerbread men were harmed in the making of this programme.
22 December 2017

Interview with 

Chris Brackstone, University of Cambridge

Gingerbread men

Gingerbread men


Now for the main event - the food! The turkey’s been cooking for hours, someone’s already pinched a few pigs in blankets and yet, somehow, you still find room to scoff a few festive treats. Izzie Clarke went to the Department of Chemistry to meet Chris Brackstone to explore how food gives us energy, and we should warn you; A few gingerbread men and some jelly babies were harmed in the making of this programme…

Chris - Okay. We’ve got a large test tube that’s got potassium chlorate in it, which is used as a source of oxygen, and a large burner underneath to make it molten and boil. That’s going to give us our heat source and our oxygen and our poor little jellybaby is going to give us our sugar. If we scale it up to what happens in our own bodies, we use sugars and our own internal heat source and the oxygen we breathe in to get energy from the glucose and the carbohydrates.

Izzie - It turns out when you drop a jellybaby into molten potassium chlorate a rather violent reaction kicks off…

Oh my goodness! I mean there’s nothing left of it.

Chris - No.

Izzie - It  started off with a slow burner and then, all of a sudden, it got this amazing purple light. This isn’t exactly what’s going on inside our bodies is it, because we don’t all sort of burst into flames when we have a jellybaby?

Chris - We don’t no. But we do get a certain amount of energy from the sugar and there’s a whole process going on - we’re like a little chemical factory. We’ve obviously got far less oxygen in the atmosphere that we’re using. We’re a lot cooler and we ourselves need to slow the whole process down anyway. There are various biological processes going on that slows that whole process down and lets the energy release more slowly.

Izzie - The processes going on in our body to release energy are a lot slower. And this exploding jellybaby showed me just how much energy is in these sweeties even if, thankfully, we don’t go up in flames. So which Christmas calorific snack releases its energy in the most spectacular manner? We lined up the treats and put it to the test…

First up were some gingerbread men and, for this demo, Chris had prepared some liquid oxygen to speed up that burning process…

Chris - I’m going to pour that over the gingerbread men. Are you ready?

Izzie - I’m ready.

Chris - See how this goes…

Izzie - That was quite the send off. My goodness! We had a huge orange flame right in the middle of that. Our poor gingerbread men have been left - they’re rather barbecued.

Chris - They are. Plenty of calories I think.

Izzie - Plenty of calories. Okay. We’ll move onto the next one and see how the Christmas cake does…

Chris - I’ve never burnt Christmas cake before…

Izzie - It’s not as an intense flame as the gingerbread men. It was more of a slow burn right round the edges and it seems to be that it’s just the icing. The really sugary icing and marzipan that is really taking up in this flame.

Chris - Indeed. It definitely does, doesn’t it.

Izzie - So the gingerbread men are still in the lead at this rate. Let’s try our third and final test - the well loved mince pie…

Oh and they’re off! Oh my goodness! We’ve got little bits of pastry flying off at different corners. The flames going lots of different blues and greens and yellows and oranges. And those mince pies have been absolutely incinerated.

Why was that flame so much bigger than the other two that we saw?

Chris - Most of the moisture has gone out of them so it is pretty much just pastry and whatever filling was in there to start with.

Izzie - Was in there! It’s certainly not there anymore.

Chris B- There’s not much left is there? They’re very reminiscent of the last time I tried to bake anything I must admit.

Chris S - Note to self, don’t let Izzie near your kitchen. Alex - can tech save the day in the kitchen when you’re trying to prepare your christmas dinner in a hurry?

Alex - I saw two really cute new bits of tech recently that I think would make your Christmas day a bit easier. The first was an intelligent cocktail-making piece of kit that makes your favourite cocktail...

Chris S - That’s me!

Alex - … in under five seconds.

Chris S - Oh, I’m not that quick.

Alex - Exactly. So that’s the first bit I thought that was really really cute. The second bit, and now this is just for fun, was a butter knife that uses your body temperature to cut the butter if it’s cold straight from the fridge, which I thought was just genius.

Chris S - This is a knife at room temperature and it cuts butter out of the fridge?

Alex - It uses your body temperature to cut the butter straight from the fridge.

Chris S - That sounds like money for old rope. It’s like you hold a knife and warm it up and cut butter with it?

Alex - It’s probably one of those things that you get and you think I don’t know how I lived without it.

Chris S - I bet you owned one of those lock de-icers that you got for Christmas which you sort of slide that thing out and this long prong comes out and you put it in your lock in your car to de-ice your lock on a cold day. Did you have one of them?

Alex - I haven’t got one of those but if was going to prioritise one of the two I’d go for the cocktail maker.

Chris S - I owned one - I never used it. I’ve been dying for a cold enough day when the lock froze on my car and I could actually use it.


Hugh - Presumably that butter knife it must be a really good metal with a really good thermal conductivity - like silver. So maybe that explains why in the old days butter knives were made of silver.

Alex - Ah, there we go.

Chris S - Was it made of silver?

Alex - I don’t know. I’ll have to look that up. I’m sure it wasn’t because it didn’t look like it cost the earth, so I’m assuming it wasn’t made of silver.

Hugh - Maybe it’s made of something like uranium or plutonium, so it’s producing heat.

Chris S - Highly likely Hugh!

Alex - Oh dear, I’m worrying.


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