Sizzling BBQ Science!

Let's tuck into a Naked Scientists' BBQ...
04 August 2020
Presented by Katie Haylor, Chris Smith
Production by Katie Haylor.


picture of food cooking on a bbq


This week, we’re getting stuck into some sizzling science! It’s BBQ time, and we’re going to explain the chemistry of cookery, the science of tastes and flavours and we’re also going to try to cook something you wouldn’t think was possible on the barbie. Plus news of the UK government’s plan to battle the nation’s bulge, but will it work?  Why leaves on the line really is a reasonable excuse for late trains. And what happens when cats and dogs catch coronavirus?

In this episode

Measuring an obese stomach

01:03 - Analysing the UK's obesity strategy

What exactly is the UK goverment's new obesity strategy?

Analysing the UK's obesity strategy
Dolly Theis, Cambridge University

This week, there were stark warnings from Boris Johnson that the world faces a second wave of Covid cases: Germany had Spain have seen big increases in cases; Melbourne has declared a curfew, and parts of England are seeing new control measures introduced. And perhaps with this in mind, the UK government unveiled plans to confront one of the big risk factors for severe coronavirus disease, and that's obesity. The Department of Health have published a policy document setting out a strategy to tackle the growing problem. Dolly Theis is a public health researcher at the University of Cambridge. She looks at the effectiveness of policies like this. Chris asked her what she made of the measures...

Dolly - So the government have brought in a new obesity strategy, a number of recommendations, including a better health, public information campaign designed to encourage people to lose weight. They're also expanding services locally to help with people who are already living with obesity, and then a whole range of other measures that help make the environment a healthier place for people, to make it easier to live a healthier life.

Chris - They don't hold back on their punches because right at the top of this report, they point out look, 63% of adults in our country are overweight. That's a pretty big number. And then even more damning, they go on to say, well, a third of children leave primary school overweight. And a fifth of those are already obese. These are kids who are not even into their teenage years yet.

Dolly - Yeah. I mean, as you say, the numbers speak for themselves. Sadly, we've known about this for a long time, but it's very difficult, because it's such a complex area, to know what can be done. And we often hear people say, there's no silver bullet i.e. there's no one thing that will be brought in that can help tackle this issue. So it requires a multi-action approach, which is exactly what this obesity strategy is clearly trying to do. We need these policies, not just to be proposed, but they need to be followed up. They need to be implemented and acted upon and evaluated. You know, are they actually going to work? We can only find that out if we evaluate them.

Chris - But Dolly, when I went to school, I know for a fact that a fifth of the kids in my class were not obese. I can't actually think of a single child in my class that was, so why are we in a situation now where we have got young children going to school, and they're already overweight before they've even set foot in the school gates?

Dolly - Yep. You're absolutely bang on with that. And this is something that a lot of people are trying to study. What we understand to have changed is that we do all want to still be fit and well, but it's not always easy, in the world that we live in. This obesity strategy is trying to tackle the bombardment of junk food advertising. We know that companies spend much more on junk food advertising than they do on healthier advertising.

And so they're bringing in, looking to bring in a ban of junk food advertising before 9:00 PM on TV and online. It's also very confusing, the information available to us, you know, we're told we should be losing weight, for example, by an information campaign. But at the same time, our high streets are often littered with takeaways. It's not always easier to cycle for example, than it is to drive. It is not easy in the current environment for everyone to live a healthy life. And sometimes it can be confusing, trying to navigate, what is a kind of healthy life versus unhealthy options.

Chris - Let's just look through some of the things that the government have earmarked that are part and parcel of their campaign. Lots of the interventions that are more carrot than stick for instance, they've got a traffic light system on foodstuffs to encourage people to make more healthy choices, labeling up food with calories. Well, that's not new. We've been doing that for a long time. Adding the number of calories there are in alcohol cause people often don't appreciate that. Fair enough. That would be a new intervention, but this is very much, again, the onus is on a person to see that information, take it on board and then act on it. Do you think that's actually gonna work?

Dolly - Oh, well, you nailed it. What you're talking about is, the kind of intervention differences that require an individual to use their own resources. So they need to engage, as you say, with the information. They need to want to turn it into action and do that over a long period of time. Whereas the interventions like the banning of junk food adverts, this takes away those adverts for people so that you're not having to make that choice. Actually, on the menu labeling front. This is a very interesting intervention, because it's proposed in a way, that it's a consumer tool i.e If you put information on a menu in a restaurant, then people going there will be better informed about the nutrient contents of the food.

Actually, the evidence on how effective that is, is mixed. What we found in a study that me and a colleague published last year is that having labeling, actually is associated with healthier food served. Maybe it's the restaurants that have labeling have healthier foods. So they're more likely to be okay with having the information on there, or it might be that because they've introduced labeling, and know what's in their food, they've then improved the healthfulness of it. So actually this kind of intervention could be seen, rather than being seen as a tool for consumers to better understand the choices that they're making. It could be seen as an information tool for the restaurants to know what's in their own food so that they can then make it healthier or provide different, healthier alternatives alongside other less healthy alternatives.

Chris - So you're a bit lukewarm on some of that, then. Some of it, you can see a benefit, but some of it very much the onus is being pushed very much onto the consumer. What do you think then about the proposed legislation to limit things like buy one, get one free deals, where the buy one get one free is for something that's really bad for you. Limit the ability of supermarkets to sort of force feed us bad stuff, that's high in fat, high in sugar, high in salt, et cetera.

Dolly - Yeah. So again, it comes back down to re-balancing things so that it's just easier to be healthier, and how that's done, these are all sort of, possible techniques to help achieve that re-balancing. So that it's just easier, so that people don't have to think too much about it regardless of where they live, regardless of the challenges that they face on a daily basis. So these sorts of techniques, we will basically have to introduce and evaluate to understand the true impact. And this is a critical part of what I'm looking forward to seeing hopefully more information about when it comes to this strategy, is it's only by introducing some of these higher level interventions, that we can actually start to build the evidence on them.

And actually there are some things that we just simply can't build the evidence on until they're introduced, a bit like the soft drinks industry levy, or the sugar tax as lots of people know. It's very hard to build evidence on the effect of a tax in a particular country without introducing the tax in the first place. So I very much hope that the evaluation side of this new strategy is taken very seriously and not retrofitted at a later stage. We really need to view introducing these measures as not only tackling the obesity issue, and the kind of food culture issue, but also helping build the evidence base on some of these interventions.

image of a train track with trees either side

08:42 - Chemistry of leaves on the line

Why are leaves on the line really a problem for trains?

Chemistry of leaves on the line
Michael Watson, Sheffield University

Along with “the wrong kind of snow” the station announcement about the delay to trains because of “leaves on the line” causes much derision and eye-rolling among disgruntled passengers, who often think it’s a made up excuse. The phenomenon is, however, a real one and can be a hazard when trains slide past platforms, and very dangerous when they can’t stop at red signals. Steel wheels on steel rails just don’t get on with leaves.

Michael - They make the rails really slippery. So the train tries to brake, it will just slide over the rails and it can miss stations. And because of that, we have to change timetables in the autumn. And the other thing they can do is when they build up in thick layers, they can electrically insulate the train from the track. And that means that the signals don't work properly, because they rely on conduction between the train and the track to tell where the trains are in the network. We tried to strip back the system and make it as simple as possible, while still making a very low friction.

That was Sheffield University’s Michael Watson. And in research published this week, he and his colleagues think they’ve figured out what’s going on between the leaves and the rails to cause the low friction conditions. By brewing up some sycamore leaf tea and one by one eliminating potential culprit chemicals, they think that tannins - which, by coincidence are also in the tea so many of us enjoy - are to blame. Michael told Katie Haylor what they did, and firstly how they ended up pointing the finger at tannins...

So instead of using leaves with all their complicated parts, and instead of using real world contamination, we use leaf extracts. So this is essentially tea that we've made out of Sycamore leaves. And we found that we could get extremely low friction with that tea, so that already rules out anything that doesn't come out in the tea. So all of the things in the cell walls, and then we looked at that extract and we removed things to see which ones when we removed them, caused the friction to increase.

Katie - So you're trying to detective-like investigate the culprit by finding which ones it isn't.

Michael - Yeah, that's right. Yeah. Chemically in our setup, we have this leaf extract, which is slightly acidic, and that will dissolve the iron, which came from these test samples. But in a real railway would come from the rails. When that dissolves, the iron ions are floating around in the solution, and they get grabbed by these tannin molecules. And because each ion can get grabbed by multiple tannin molecules, and each tannin molecule can grab multiple ions. By the end of this, you end up with this big, loosely bonded, cross-linked network. And that's what really causes the low friction.

Katie - And this is the black, kind of, gooey stuff that's causing the hassle, right?

Michael - Yeah. So when these tannins grab the ion, they also leave the solution and they turn into a black precipitate, solid, that's floating in the solution.

Katie - Okay. So the theory is, you've got leaves falling on the track. These leaves are what, degrading a bit? And there's some sort of acid there. That dissolves iron from the tracks, and tannins from the leaves grab onto these iron ions, making this low friction producing black stuff.

Michael - Yeah, that's exactly right.

Katie - Great. What's going on at a molecular level though? Why does this black stuff have such low friction?

Michael - We think the cause of the low friction is because it's very thin. It's almost as thin as water. So it's not viscous like honey, but when you compress it on a sort of micro scale, when the surfaces are contacting, it gets compressed very hard into this hard black plastic. And that means that you don't get the viscous drag that you would get if you're in something like honey, but the surfaces can't touch each other, because every time they get near to touching, it turns into this harder plastic. So you end up with the sort of, best of both worlds way of reducing the friction.

Katie - How comparable is your experiment to what's actually happening?

Michael - We've shown one thing that does cause this very low friction, but we can't take the results from this and say that we're definitely showing the only thing that can possibly cause low friction. You have to take it with a pinch of salt, but it's the first time that anyone has linked a particular chemical to the very low friction that they get on the rails.

Katie - What are the options for actually preventing this from happening? Because I guess that's the goal, right?

Michael - Yeah. So either you can protect the rails from corrosion, which you might want to do anyway. Or you can put your own chemical down that will grab the iron ions better than the tannins can, so that when the iron ions come out, they don't get grabbed by the tannins. They get grabbed by your molecule instead, and then they can't make this big complex. Something we would like to keep working on. But as the labs are all closed now it's hard to get anywhere with it now.

Katie - I see. So we need to watch that space. But it's interesting you mentioned the tracks, because I was wondering is the iron the thing that's the problem? Would it at all be feasible to just change the track material in at risk places?

Michael - Track materials have been around for a very long time and people have spent years and years optimising. So the materials we have at the moment, are quite complicated materials, and swapping it to something like nickel, you'd really be taking a leap into the dark. And it'd be very, very hard to justify doing.

Katie - What about the trees though? Does it depend on the type of tree, and is felling an option? Cause there's an environmental cost to that. Right?

Michael - Well, felling is something that happens anyway. It's the method of last resort that Network Rail have. If they need to sort out a black spot. With this research, we can talk about which trees contribute the most. So we might be able to reduce felling where it happens with it still being there as a last resort.

Katie - And is that a case of which leaves contain the most tannins?

Michael - Yes. Yeah. That should be it. Well, we know that oak and sycamore are very high in tannins. They're also very common in problem areas. So that's what we use, sycamore, in the study, but there's also a lot of anecdotal evidence surrounding oak.

a ginger tabby cat scratching itself

16:29 - Can cats catch Covid?

A pet cat in the UK has been diagnosed with Covid...

Can cats catch Covid?
Sarah Caddy, Cambridge University

A couple of months ago we heard about Nadia the tiger at the Bronx Zoo in the US testing positive for coronavirus. And this week a 6 year old female Siamese cat made the news as the first animal to test positive for the disease in the UK. So could our pet cats and dogs be carrying the infection, and could they pass it on to us? Sarah Caddy is a vet and researcher at the University of Cambridge, and she spoke to Chris Smith...

Sarah - Well, from studies of cats in a laboratory, it seems that the majority of cats don't actually get any signs of disease at all. Even if you give them quite high doses of infection. But we don't actually know if this really reflects what happens in a real world. So we're recommending that cat owners look out for similar signs you'd see in a human for COVID-19.

Chris - Can they actually die of the disease or is it just generally trivial symptoms?

Sarah - There's been no cases that we know of that have died from the virus at all. The reported cases have only had very mild symptoms. So the cat in question UK, had a runny nose and possibly a little bit of difficulty breathing, but certainly nothing life threatening.

Chris - How do you think the cat got it then? And how do cats transmit the infection? The same way we do?

Sarah - The particular cat in the UK, we know the owners of this cat were diagnosed with COVID-19. So in this case, we know that it went from owner to cat. And the other cases that have been reported worldwide, we think is a very similar situation. In terms of transmission, we expect it to be very similar methods for human to human. So droplets or aerosols, or very close contact between cats or between cats and humans.

Chris - The critical question of course, Sarah, is if it can go from human to cat, can it come the other way?

Sarah - There's no evidence that this has occurred, but as it is theoretically possible, we are recommending that any humans with Covid symptoms are employing very careful hygiene around their own cats and making sure you're washing hands and avoiding really close contact if possible.

Chris - What about other family pets? Cause obviously some people are cat people, some people are dog people, some people keep birds. We've been asked about the risk of all of the above.

Sarah - Absolutely. Experimental studies have suggested that dogs don't become readily infected with the virus. But having said that, a number of dogs worldwide have been detected to have virus in their bodies. Some dogs are known to make an antibody response, or an immune response, to the virus suggesting very low levels of infection, but we don't think they're as susceptible as cats.

Chris - And what about pet birds? Cause someone wrote to me about their budgie. Is that at risk?

Sarah - Going back to again, the experimental infections, chickens and ducks showed no evidence of getting infected at all. And that's as far as we know about birds actually. So I'm certainly not worried about pet budgies.

Someone shining a light up from a mountain at the stars and Milky Way.

19:38 - Best place to stargaze on Earth

Where on Earth can you get the best view of the heavens?

Best place to stargaze on Earth
Matt Bothwell, Cambridge University

If you like looking at stars and other heavenly bodies in the night sky you’ll know that using your telescope in a city or other place with lots of light pollution is not a good idea. It’s better to get out into the countryside where the further you are away from street lights and vehicle headlights the better. Taking it to an extreme though, you are going to have put on your thermal underwear and hiking boots. A few huskie dogs might come in useful too! That’s because Chinese astronomers have discovered that the best place on Earth to stargaze is in Antarctica. It’s on top of a mountain of ice called Dome A, and it’s 12 hundred kilometres from anywhere. Astronomer Matt Bothwell has been reading the research and he told Phil Sansom what makes this spot so special...

Matt - It's a general problem for astronomy that we are living at the bottom of a very thick atmosphere. I mean, it's nice for human life on Earth that we don't all die! But for astronomy, it's quite difficult that all the nice signals from space have to travel through hundreds of miles of air before they reach our telescopes. And air isn't perfectly transparent, right? Anyone that has seen a mirage wobbling around or seen light wobbling around above a heat source, like a radiator or a fire, will get the idea that light can bend and twist as it travels through air.

Phil - That's why the stars twinkle, isn't it?

Matt - Yes, exactly right. That's why stars twinkle. Astronomers called this "seeing", which is a fairly obscure word. don't know why we call it this! But yes it's the seeing is what we call the amount that light is kind of blurred as it travels through our atmosphere. And the real trick for astronomers is to find places where the seeing is really, really good, where the atmosphere is nice and calm and still. And we can take very nice, clear pictures of space.

Phil - That's why astronomers like Hawaii, for example, right? Or big high mountains. Isn't it?

Matt - Exactly. So Hawaii is famously good for this. The Atacama desert is famously good for this. And what this new paper has found is that there's this particular site in Antarctica called dome A where the seeing is maybe better than anywhere else on planet Earth.

Phil - How much better?

Matt - Astronomers measure seeing in something called arc seconds. An arc second is a very, very, very tiny angle. So one arc second is 3,600th of a degree. And it's basically how much the light from a star or light from a galaxy has been spread out by the atmosphere. If you have seen below one arc second, that's generally considered pretty good. Down here in Antarctica in dome A, the seeing gets as good as around 0.1 arc second, which is absurdly good. Much, much, much better than anything you would ever see in Hawaii or Chile.

Phil - Is this sort of like a measure of how blurry the stars are when you look at them? And so this place, if you look up to the stars, they're 10 times clearer than this gold standard?

Matt - Yes, that's exactly right. So 10 times clearer to our telescopes.

Phil - Where is this site exactly?

Matt - So it's called dome A, it's in the Antarctic. I think it's relatively close to the very slap bang center. It's essentially one of the highest points in Antarctica and about four kilometres above sea level.

Phil - What would this make a difference for? What kind of thing would this be useful for?

Matt - Okay. So I would caveat this with the fact that I'm a long wavelength radio astronomer. I don't really do much short wavelength like optical astronomy type stuff. But getting better resolution in telescopes is all about being able to see objects that are close together. And so two binary stars, for example, might blur into one, if you have bad seeing, but with this crystal clear seeing, you'll be able to separate them and see that they're actually two separate stars. Or exoplanets, for example. So planets orbiting other stars, is one of the really hot topics in astronomy nowadays. We want very, very, very good resolution to be able to separate out systems like that.

Phil - Is it really worth carting a whole bunch of really expensive telescope materials out to this isolated part of Antarctica? I mean, is this sort of untamed wilderness, are there already people there, or what?

Matt - I would say it's, it's a lot closer to untamed wilderness than almost anywhere else on Earth. Building anything down in Antarctica is going to be a very, very substantial thing to do. But I do think it's going to be worth it, for a given value of it's worth it, right. Getting a telescope to the best place in the world to observe the universe would be very, very valuable.

photo of a man cooking meat on a bbq

Let's get this BBQ started!
Tristan Welch, Parker's Tavern; Eleanor Drinkwater; Barry Smith, SAS; Jane Parker, Reading University

It’s August, the sun is shining - at least, for the minute - and we’re in the holiday spirit! So what better way to celebrate than with a BBQ! Cooking and eating outside can feel and taste like a real treat. First up, Chris went outside to his sunny garden and got the BBQ lit...

Chris - Guess what, in traditional British fashion - it's raining! It has literally gone from sunshine to rain. You would not believe it. I am of course, here with Tristan Welch. And he's been actually knocking up this cake because we are going to cook a cake on a barbecue. If you didn't believe that it was possible, keep tuned in to see history being made. It can be done. So just remind us, what have you put into these cakes Tristan? And how are we actually doing this?

Tristan - Right. Well, first of all, I've got to say, this is not the first time I've ever cooked a pineapple upside down cake on a barbecue, but certainly is the first time I've cooked in the rain! So I've taken the butter and now what you can hear is the sugar and butter in there together. That's being creamed together, so it's a basic sort of sponge mix. To that I add our eggs. Give that a jolly good mix. Then our flour and we're using self raising flour. Now I've taken tinned like individual small little tins. I think they're 250 grams, 240 grams of sliced pineapple. I've taken the top off, poured out the juice, drank it actually, put a one slice of pineapple back on the base with some golden syrup and a cherry in the middle of the pineapple slice. And I'm just about to pop this cake mix on top of it.

Chris - Just the quick rundown of the ingredients in terms of what sorts of proportions? How much of each?

Tristan - 150 grams of unsalted butter, 150 grams of caster sugar, so there's equal quantities. To that I added two eggs and now I've just added 150 grams of self raising flour. We give that a jolly good mix, and that will be quite a tight mixture. So then we add a couple of tablespoons of milk and that loosens it up. In the bottom of the tin I put in about a tablespoon of golden syrup, and one slice of pineapple with one cherry in the middle.

Chris - And then you're going to spoon in, what, fill that in to the brim with mixture?

Tristan - Yeah, take this mix. And this mix fills about four tins up quite nicely.

Chris - Okay. And that then goes - we've got a barbecue with the lid - that's probably important is it? Cause we're basically using the barbecue as an oven.

Tristan - It's vital. So the actual thought process behind it is the heat from below is quite aggressive. So that's going to boil the syrup and the syrup will protect it and prevent it from burning. The lid creates the oven like effect. So it will bake as an oven, but be able to take the aggressive heat from below.

Chris - Temperature gauge says about 200. Is that, 200C, bit hot?

Tristan - That's about right. That's about right. With barbecuing it's about using your senses and feelings and you know, after five minutes you can see it starting to bubble up. If it's not burning it's okay. But definitely around about the 200 mark is about perfect.

Chris - How long do you anticipate we're going to need to put this on for?

Tristan - I'd say about 15 to 20 minutes.

Chris - OK, thanks Tristan! Also with me is biologist and champion of the world of creepy crawlies, well known to The Naked Scientists, that's doctor to be (soon), Eleanor Drinkwater. She's just a gnat's whisker from handing in her PhD thesis. Welcome to the show, Eleanor, you've brought along something for the feast. What is it?

Eleanor - Yeah. So I brought along some edible crickets. In a variety of excellent flavours as well! So these guys haven't actually tried them to my knowledge. Is that right?

Chris - You're going to make me and Tristan eat in insects?

Eleanor - Yes. You're going to discover how wonderful insects are. It's probably going to change your life.

Chris - I have to say Katie, that actually I knew Eleanor was on form. Cause I came out to start the show and she's already caught us a wasp and got it under a glass buzzing around on the table. And I said, " are we going to barbecue that?"

Eleanor - No, no, no, no, no, no. You have to watch it and admire it before letting it go very gently. That's what you have to do when you find a wasp.

Katie - You're very brave for catching wasps. I am not a fan. Sadly, no barbecue for me over here in the studio! But to console me down the line is a flavour chemist Jane Parker from Reading University. Jane, what does a flavour chemist get up to?

Jane - Well, we do a lot of sniffing and our job really is tied to identify the key aroma compounds that are in the foods and work out how they're formed and how they interact with other components in the food. And how they're released and eventually how we actually perceive them. So it's the whole story really.

Katie - Sounds delicious. And we'll come back to you very soon. Also with us is sensory scientist Barry Smith. Barry, how does your research relate to food?

Barry - Well, I'm interested in finding out what happens in us once these wonderful flavour compounds have got together in the way that Jane described. So I look at the science of tasting and I'm looking at how our senses work together, touch, taste, smell, maybe sight, maybe sound, to give us that unique experience of the flavours of foods that we like.

image of meat cooking on a BBQ

30:06 - Yum....chemistry of flavours

What's the chemistry behind why food can taste so delicious?

Yum....chemistry of flavours
Jane Parker, Reading University; Tristan Welch, Parker's Tavern

As chef Tristan started his cake and sausages cooking on the Naked Scientists BBQ, Katie Haylor asked chemist Jane Parker about the science of flavour...

Chris - Right Tristan I suppose you've now got the tins full. So you've got greaseproof paper lining the tin, there's the piece of pineapple in the bottom with the cherry. Spoon the mixture on top, and now what are we doing?

Tristan - So we use the tin to bake the actual pineapple upside down cake. I've lined it carefully with greaseproof paper, popped up on the grill, so there's intense heat coming from underneath it. And we're going to pop the lid down, let it bake essentially.

Chris - You've also got them on there alongside the sausages, you're cooking up some nice sausages. We're not going to get sausage flavoured upside down cake though?

Tristan - Maybe this is a new thing, who knows? I think we'll get some of the smoke from it. And that's a really important part of the flavour and all this sort of stuff. But it's one of those sort of crazy days with pineapple upside down cakes, sausages, and cake, and cooking in the rain, right?

Chris - It's already smelling really delicious. Katie get a quick whiff of this down the mic...

Katie - Oh haha! I'm so jealous!

Chris - I mean this is the sausages. Oh, it smells amazing, I'm telling you!

Katie - Jane, you're a flavour expert. Before we, well, before they get to try some of this delicious food, what exactly is flavour? Are we talking smell, taste?

Jane - Well all these words - flavour, aroma, taste - all get a little bit confused in the English language and as scientists, we've got a clear distinction between them. So taste is what you perceive on the tongue. So that's things that are sweet, sour, salty, bitter, and umami, which is the savoury taste. And aroma is what you perceive in the olfactory bulb through your nose. And these are very volatile compounds. The combination of these is what we describe as flavour. And as Barry was alluding to earlier it's flavour, aroma and taste, but it can also be colour and texture and sound and other things as well.

Katie - But how will those pork cylinders that they've put on the barbecue, how will they translate to sausages in their brains? What's going on?

Jane - Well, to start off with as you start cooking the sausages you've got changes in the protein structure as it denatures and aggregates again to tenderise. And you've got colour formation, but the key thing is the flavour that's developing. And there's four different ways that you can develop flavour while you're cooking sausages. And one is the Maillard reaction that's very well known, and it's the reaction that occurs between proteins or amino acids really and sugars as you heat things up. And that gives you these roasty, toasty, and meaty aromas. Fats - they start to degrade as well. And when they degrade, they release aroma compounds. And these help you work out whether it's a beef sausage or a lamb sausage or a pork sausage, because they give you that ‘species’ character. These go on when you're cooking meat anywhere, but once you're putting things on the barbecue, you're starting to get caramelisation as well. So that's when the surface is really hot. And if you've marinaded your pork sausage in anything sweet and sticky, you'll get even more caramelisation going on. And the final thing is the flavour that comes from the charcoal itself. The charcoal is made from wood, wood contains lignin, and there will probably be some remnants of lignin in your charcoal. And as you burn the lignin you generate a lot of smokey and spicy compounds, which are phenols and glycols, and you can even get vanilla as well. So you can get quite a fragrant aroma. And we've got some sunshine over here and that's a smell that's coming in through my window as my neighbours are barbecuing. It's definitely that smokey element that gives the key barbecue element to your sausage.

Katie - It sounds delicious. I really wish I'd had some dinner before the show. I think Chris' barbecue, is it gas, Chris?

Chris - Yeah. I was just listening to what Jane was saying and thinking: oh dear! Because I've subjected Tristan to cooking on gas, is that bad? He's shaking his head and he's rueing the day.

Tristan - It's a little bit of a faux-pas to be honest.

Chris - Ah sorry Tristan! So is that a problem, Jane? Can I get away with this?

Jane - I think you can get away with it because you've got the high temperatures. You've got the Maillard, you've got the flavour from the lipid and you've got the interactions...

Tristan - I almost went home!

Chris - It's a no from Tristan Jane

Jane - Oh dear. I'll leave. I'll go home!

Tristan - I'm a temperamental chef!

Katie - Oh dear!

Tristan - It's alright, I think actually it works because you've got the fats hitting the flame and the flames are licking the outsides of the sausages and stuff like that. So it works. But there is a little smokiness that you get from the charcoal, which is something really special.

Katie - Chris, I'm rather jealous.

A man's nose.

34:29 - Sensory science and Covid

What is parosmia, and how does it impact eating?

Sensory science and Covid
Barry Smith, SAS; Jane Parker, Reading University; Tristan Welch, Parker's Tavern

With the cake half way cooked on the Naked Scientists' BBQ, Chris Smith spoke to sensory scientist Barry Smith and flavour chemist Jane Parker about the sensory experience of food, and how Covid-related changes in smell and taste can impact how Covid sufferers experience eating...

Chris - We are making a cake on the barbecue. Tristan, do you want to give us an update? How are we doing? It's been on what, 10 minutes?

Tristan - Yeah, and you can see the cake mix is bubbling up. It's rising. They look like mini souffles almost, but the top of the paper is starting to toast a little bit with some of the mix that's stuck on the side. That's a great indicator that -

Chris - We're not going to eat the paper, are we?

Tristan - No, but it's just an indication that things are cooking. Well, I dunno, maybe. I mean, sausage-flavoured upside down cake. You never know!

Chris - No, seriously, this is amazing. They've risen right out of the top of the tins and they're beginning to look really amazing, as are my sausages. And it smells good!

Tristan - Yeah, it smells great doesn't it? I've got to say that they are bubbling away beautifully. Just gonna take a few more minutes!

Chris - He's a confident man isn't he! With us also is Barry Smith who's a senses scientist and is joining us to tell us about some of the ways in which my senses are being stimulated today. Now Barry, people characteristically say that things do taste better when cooked and consumed out of doors. Is there any science behind that?

Barry - I think there might be. I like the idea that our senses are being bombarded while we're waiting for the food to cook. We're seeing the colour of the flame. If you had charcoal Chris you'd have a lovely grey-blue flame there. You're smelling the barbecue. You're hearing the sizzling and all of these things are giving you expectations about what you're going to taste. And they're probably giving you expectations that are going to bias you and make it even more pleasurable to taste the food. People are also tempted, I think, when they're eating barbecue food to eat with our fingers. And of course that's a very natural thing to do. People say we eat first with our eyes, but we eat second with our fingers. Picking something up you will gauge from your fingers, which are very sensitive, what's the texture of this? Is it sticky? Is it sharp? Is it crunchy? It's soft, squidgy? And that gives you a good expectation about the texture as you put it in your mouth. So I think all of those things are being primed especially well. If you're in a kitchen, you might smell the cooking smells, but things might be in the oven unseen. You don't see the smoke and you don't want that indoors. So I think this is making a big difference.

Chris - In terms of flavours and things, Barry - you were talking about the sort of tactile nature of food and that being important, that sensation is obviously being integrated with all of the other assaults on your senses when it comes with eating posh-nosh and fine food. If you make the food spicy, that's not actually a taste or a flavour is it, the spiciness? It's just a burning sensation. But does that add a dimension as well? Is that an additional stimulation that makes the food have an extra something?

Barry - Yes, it does. This is one of the hidden flavour senses and it's employing the trigeminal system. So as you know, Chris, the trigeminal nerve is the fifth cranial nerve. It comes from behind the ear. It goes to the eyes, the nose and the mouth. And it's the one that rings bells when you have too much wasabi and you feel it at the bridge of your nose, you feel that ouch sensation. And also if you have too much irritation of the trigeminal nerve, the eyes will water because they think they're under attack when you're having too much spice. That trigeminal nerve makes peppermint tastes cool in the mouth, mustard taste hot, and therefore even spices like vanilla - which seem very gentle, it's a spice - these are just giving you that tingle. Ginger, obviously garlic, all those other things, black pepper. And these are wonderful flavours to add. So you need touch, you need taste, you need smell, and trigeminal stimulation to get the flavours we love.

Chris - I've got to ask you Barry because of course, in recent months, we've seen the case definition for a person with coronavirus change. It went from just have you got a cough and a fever, to have you got a cough, a fever, have you lost your sense of smell and taste. So what's the implication for people who have had coronavirus and have seen their sense of smell and taste change in response to this?

Barry - Well this is very well known to Jane and to me since we were part of a team with colleagues from ear nose and throat surgery campaigning to get the government to recognise that loss of smell and taste were symptoms. So very often people will say, I've lost my ability to taste food. Now, when that happens, I'm not sure it is taste. I think it's mainly smell. And I usually ask them to put a bit salt on their tongue, a bit of sugar, or lemon juice, and I say can you taste that? And if people say they can taste that, but that's virtually all they can taste, then you know what they've lost is their sense of smell. And it's really at that point that they recognised how much smell was contributing to the pleasure of eating. The fruity notes, the meaty notes, that taste of an onion, none of that comes from the tongue - that's all combining what the tongue provides with aromas in the nose. So a lot of people started to say their food was dull, their coffee tasted of nothing. And of course, if you think of coffee without the wonderful smell of freshly brewed coffee, it's just hot water with a bitter flavour. So a lot of people noticed first in their food that they were lacking their sense of smell because of one of the symptoms of COVID-19. And probably because the nose is a major infection site for the virus.

Chris - This is dubbed parosmia, isn't it, Jane? What are you actually doing to try and understand more about what flavours people can and can't perceive? And is it true also that people are saying that when their sense of smell and taste does begin to return post-COVID that actually it doesn't come back all at once and everything begins to taste normal all at once?

Jane - Well, what Barry was describing was anosmia, and that's when you completely lose your sense of smell. And many people with COVID will get that back after several weeks. But some of the more unfortunate people, it will linger for a bit longer. And one of the things that happens in the recovery process is the parosmia which is when everyday smells can be distorted and are repulsive. And frankly, people in severe cases, they can't be in the same room as people cooking, people drinking coffee, cooking for the family becomes a problem. Eating becomes a problem. It can have an impact on mental health. So we've been carrying out a study, which started before COVID, because this also happens with other viruses - so it's known before this parosmia phase. So we've been looking at what foods in particular trigger this parosmia, because it's only certain foods. And then what chemicals, what aroma compounds in particular. And I have to say that a barbecue must be a parosmics nightmare because the things that we're finding that are triggering parosmia - coffee is one of them and coffee is the most common, but after that it's meat and chicken and beef. And it's the cooking process, which is often described as the worst. It's onions, it's peppers, it's cucumber. So even the salad, it's not just the cooking process. You know, it's a series of really potent aroma compounds, which are the triggers.

Chris - What could a person who's suffering with this expect then? And what can they eat?

Jane - Although we've got a group of things that parosmics tend to hate, the things that they like is a lot more variable. But it's generally bland things, it's pasta, there's a lot of fruit and veg that is okay for many parosmics, but it's not without exception. You know, watermelon is horrible for some people and that's really quite bland.

Chris - If you're someone who's unlucky enough to find themselves in that position, what's going to happen to you? Is this going to be the rest of your life or will it go away?

Jane - Well, the good news is that for many, many people, it will improve over time. One of the things that is recommended by ENT specialists is to carry out what's known as smell training, where you sit in a quiet room twice a day, and you've got a range of essential oils and you may smell nothing to begin with, but just that act of smelling the essential oil and thinking about it and going through that process helps you mentally. And it also helps we believe to stimulate regrowth of the neurons, which have been destroyed as a result of COVID.

Chris - Which sounds promising. So do you have any feeling yet for what proportion of people are going to improve? What proportion will probably stay the same and what proportion may even get worse?

Jane - I think it's unlikely that anybody will get worse. We just don't know because we haven't had enough people going through the parosmia stage - there's a three month delay. So we're only just now getting the influx of parosmia people. So we don't know enough about how many people will recover. I know that from other non-COVID parosmics there are some who don't recover, you know, even eight, 10 years down the line, there will be one or two. So we can't promise that everybody will recover, but most people do, but it does take years. You know, you'll make a slow change from if foods are really repulsive and horrible things will start to get slightly better. They'll never return exactly to normal, but you'll learn to live with them. You'll learn to recognise coffee as what it is now rather than hate it, but it does get there.

photo of a man smelling some pasta

44:17 - Eating with your eyes and ears

The experience of food goes way beyond eating...

Eating with your eyes and ears
Barry Smith, SAS; Tristan Welch, Parker's Tavern

As chef Tristan Welch took his pineapple upside down cake off the Naked Scientists' BBQ and let it cool, Katie Haylor spoke to sensory scientist Barry Smith about how vision and hearing come into the world of food...

Chris - Tristan, the moment of truth has arrived. We have to lift the lid on the barbecue.

Tristan - Oh ho ho!

Chris - These look really good!

Tristan - You see they're bubbled up beautifully, and they're perfectly cooked. You can see that crisp on the outside, slightly golden on the top, and if you look on the edges there, they've got that beautiful golden brown colour.

Chris - The man was right and his upside-down cakes have cooked in their tins on the barbecue. We're just pulling them off now. The sausages look pretty good too Tristan. I hand it to you, you cook a mean sausage on the barbecue, even if it is gas.

Tristan - Well, who knows, maybe I'll make a career out of it. I don't know.

Katie - Barry - my mouth is watering in the studio. It sounds really good. But what about sound and sight when it comes to food? Because we've dwelled on smell, and taste, and touch, as you said. What about what food sounds like or looks like?

Barry - All of these things make a difference. I mean, if you think of the colour of food, if the colour is wrong, you don't want to eat it. There was a lovely experiment done by Wheatley in the 1970s where he had people in an ultraviolet room eating steak, peas, and chips, and asked to say whether the steak was tender, how were the chips, how were the peas; they were discussing the food. And then he flipped the real lighting on, and you saw the steak was blue, bright blue; the chips were green; and the peas were red. And some people had involuntary retching. That's funny, because they'd already been discussing and talking about the food. So it shows you that how food looks will have a big impact on whether it's acceptable. And then of course, sound. Interesting, when we're thinking of chefs like Tristan, you're thinking of them using sound to assess their cooking. Does the pan sound too angry? Is the sizzling too high? Do I turn it down? But also, when we're on aircraft, the sound of white noise in our ears - 89 decibels or above - has an impact on the brain's ability to process information from the tongue. So salt, sweet, and sour are reduced considerably, maybe 10-15%. So if you want a better experience when you're reaching on an aircraft, take your noise-cancelling headphones; or eat something with umami, because umami seems to be immune to this effect. And what's got lots of umami on an airplane? Tomato juice, because tomatoes are rich in umami. So that's why people have bloody marys on a plane and at no other time.

Katie - What about just the beautiful outdoors? I mean, Chris and Tristan and Eleanor are outdoors. What about being able to see trees and smell grass and things like that?

Barry - Yeah, I think you're getting all of those wonderful sights and sounds. Remember, some of our happiest memories - especially from childhood, if we had a happy childhood - are being outdoors in summer, having picnics. Those are happy occasions. So the smell of freshly cut grass, the smell of all that chlorophyll; these are odours which remind us of happy occasions. And when you also think of eating outside, you're in a very natural setting, and in fact perhaps we're even reminded of some of our evolutionary ancestors. It was when they were sitting around fires, cooking food for the first time, that they were extending their daylight hours by light from the fire; they were safe from predators; they developed jaws that were not so strong, because they didn't have to have enormous bite strength to eat raw meat; they were getting these new, cooked flavours. So I think there's something almost ancestrally wonderful about watching meat colour and brown and give off roasted aromas. And then we're going to get the flavours we expect and see the smoke passing before our eyes. All of that is part of the experience of eating outdoors and having a barbecue.

photo of chef Tristan Welch displaying a cake cooked on a BBQ

BBQ-ed pineapple upside down cake
Tristan Welch, Parker's Tavern; Eleanor Drinkwater; Jane Parker, Reading University

The proof of the pudding is in the eating, as they say....

Chris - Well, Tristan's got one of the cakes out. It's on a plate in front of us. Do you want to do the honours, Tristan? Are you going to cut us a slice?

Tristan - Yeah, absolutely. Here we are. So I've just decanted the cake out onto a plate. I've pulled the paper away. I'm just going to cut it in half now.

Chris - It just looks amazing. Oh, seeing it, Tristan's just cut it in half, and the pineapple on the top, the cherry turned beautifully gooey in the middle... a nice wasp buzzing round for you, Eleanor...

Eleanor - I was just trying to catch it, actually.

Chris - The rain has stopped, which is amazing. You can work wonders Tristan.

Tristan - You catch it, I'll cook it.

Chris - Right. Are we going to go for it? Let's have a fork each. Eleanor, have a...

Eleanor - Oh my goodness, this looks incredible.

Tristan - I'm just going to use my fingers.

Chris - I'm going to try and get a bit that's got some cherry and some pineapple. Oh, this is amazing. Katie, you don't know what you're missing.

Tristan - You've had your cake before you've had your sausages there.

Chris - Yeah, I haven't had the sausages yet. I'll have one of them in a minute. Jane, you're missing out big time. Sorry that you can't have any of this delicious cake.

Jane - Yeah, I know!

Chris - The pineapple on the top - on the bottom rather, but on the top when Tristan turned them over - is this beautiful texture, and the most amazing array of flavors that doesn't taste like pineapple does when it's just raw in a tin. Why has that happened?

Jane - Well it's a very clever idea making a pineapple upside-down pudding on the barbecue, because that aggressive heat you were talking about earlier really heats and caramelises that syrup that's on the bottom. And then the pineapple: when it's fresh, it has lots of esters and some sulphur compounds that make it a bit tropical, but once you start heating it, it caramelises as well because it's high in sugar. And you get a compound called furaneol, which has got a really candyfloss, toffee-type aroma. And that really gives your pineapple that gorgeous caramel toasty aroma, because it's been in contact with that high heat on the bottom.

ants climbing on watermelon slices

49:47 - Insect invasion

Why do ants always find their way onto my picnic plate?

Insect invasion
Eleanor Drinkwater

If you eat your dinner outside, it’s inevitable that a creepy crawly or two - normally ants or flies or wasps - will want to get a slice of the action. Bug expert Eleanor Drinkwater told Chris Smith why...

Chris - Why have you put it under a glass?

Eleanor - Okay, we have here an absolutely beautiful common or German wasp. They're the gorgeous yellow ones that you see. And they are social creatures, and so they've actually been found to recruit their sisters, their nestmates. The best way to deal with one, if you have it at a picnic, is to get a glass and very gently put it under the glass to stop her from recruiting. If you kill her - which obviously no one should do - they release a pheromone from their head which would attract more. And if you leave her, then she will go and attract more. So really, if you put them under a glass and then very gently release them afterwards, that's probably the best way to deal with it.

Chris - That wasp then can tell its nestmates where the good dinner is to be had. And it will go and get all its mates, which is why you've sequestered it there.

Eleanor - Yes, exactly.

Chris - Do ants do the same thing?

Eleanor - Oh my goodness, yes they do. They are just gorgeous creatures. And what they do is, you'll have a scout who will go and find a food source, and go back to her nest. And as she does, she will leave a pheromone trail. So almost like Hansel and Gretel leaving breadcrumbs. But the amazing thing then is, as it recruits more ants to the source, they also lay the trail. So you get this amazing feedback loop: as more and more ants find the food source, you get a stronger and stronger signal, so as a result you get much greater attraction to the area.

Chris - I like the way you use the word feedback, because that's sort of really what it is!

Eleanor - It is exactly that! They have short-term pheromones - so that one will disintegrate very, very quickly once there's no longer food there - but they have a long term one as well, so the ants will stop being recruited but then occasionally go and check back, which is an amazing adaptation.

photo of a cricket on a branch

51:40 - Crunchy BBQ crickets

The team tuck into some BBQ-flavoured insects...

Crunchy BBQ crickets
Tristan Welch, Parker's Tavern; Eleanor Drinkwater; Jane Parker, Reading University

For the first course - cake and sausages! For the second course - crickets! Chef Tristan Welch, bug expert Eleanor Drinkwater and Chris Smith tuck in at the Naked Scientists' BBQ...

Chris -Eleanor, one of the reasons that you said you'd join our barbecue - because we're eating barbecue food, etc., and talking about the science of it - is you said you're going to bring us some barbecued insects.

Eleanor - Yes, I have them right here. I have salted toffee crunch roasted crickets, salt and vinegar roasted crickets, and smoky barbecue roasted crickets.

Chris - You game Tristan?

Tristan - Well, I didn't think crickets was that. But of course, absolutely. I'm completely up for it. I've never tasted bugs before other than snails.

Eleanor - Which flavour?

Tristan - Salt and vinegar please! That's my poison...

Chris - Go on then. I'll have the barbecue one since we're doing barbecue. So they're in a nice little packet...

Tristan - Oh my goodness, look at that!

Eleanor - Yeah!

Chris - Okay. So I'm just opening the packet.

Tristan - It looks like a load of bugs have got into your crisps. How do they make them crispy? Do they oven roast them, or fry them, or...

Chris - Yeah how do they make them? And why are we eating insects?

Eleanor - Sorry. I've got a mouthful of bugs.

Chris - They're quite nice, actually. I'll have another one.

Eleanor - Yeah, they are! They are really good. Eating insects is absolutely brilliant for the environment. So they're very good for you, they're very high in protein, very low in fats and that kind of thing. But then on top of that, they are very good because you hardly need any water to produce invertebrates. They're very, very efficient at turning food and water into protein. They're great for the environment. So everyone should think about trying them.

Chris - It has been catching on though, hasn't it? Because you can rear insects on the kinds of foods that actually wouldn't make it onto the supermarket shelves. So they can turn what would be trash into sort of nutritional treasure, in some respects.

Eleanor - Yeah definitely, definitely. And you have to remember that they're eaten all over the world, it's a very common thing to eat invertebrates. We're just very odd in the UK to not have entered into that. So actually we keep catching up with the times.

Chris - Serve these in your restaurant, Tristan?

Tristan - Not just yet, no. Could you imagine the crickets running around the kitchen? That'd be hilarious, wouldn't it, Oh god, we'd probably get shut down, I don't know! These are roasted? And they taste quite nice, they're crispy! Do you know, I think I'm coming around to it. It's not terribly bad, is it?

Eleanor - You mean it's fabulous? "Not terribly bad" - it's fabulous!

Chris - They are actually very pleasant, I'm very impressed. And Eleanor, thank you for introducing me to them. I would not eschew a cricket in the future.


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