Bulgaria is famous for its yoghurt, a fermented milk food full of ‘good’ bacteria that has kept hungry Bulgarians healthy for over 4000 years.

Inspired by that, and a question from a CrowdScience listener in California USA, Marnie Chesterton and Caroline Steel are immersing themselves in Bulgarian culture with a programme about Bulgarian cultures, recorded at the 2025 Sofia Science Festival.

So, are the ‘live’ cultures in fermented foods actually alive by the time you eat them, and how can you tell? If you can eat the mould in blue cheese, can you eat the mould on cheese that isn’t supposed to be mouldy? Is traditional food really better for you? And if you put a drop of vanilla into a litre of milk, how come it all tastes of vanilla?

Marnie and Caroline are joined by a chemist who was a member of Sofia University’s ‘Rapid Explosion Force’, a food technologist with a PhD in sponge cakes and a Professor of molecular biology who says that we contain so much bacteria that we’re only 10% human.

With questions on food from around the world and from the audience in Sofia, Marnie and Caroline will be digesting the answers, as well as some local delicacies.

Presenter: Marnie Chesterton & Caroline Steel

You may have grown up hearing the saying “red sky at night, sailor’s delight, red sky in morning, sailor’s warning” - or maybe a variation of it. CrowdScience listener Alison, who sees many dazzling red skies from her home in the Yukon, Canada, certainly did. And now she wonders if the saying is a sensible prediction of coming weather or just another old wives’ tale.

Alison and presenter Anand Jagatia run a little experiment, getting up at the crack of dawn and staying up until dusk for 5 days to record if the sunset and sunrise can predict their local weather.

While we wait for the results, we track this weather proverb back to its ancient roots to find out how important it may have been to the people without satellites or even thermometers to guide them.

We also tap into the expertise of modern-day weather predictors, meteorologists. What are the atmospheric pressure systems that cause red skies, and how do they influence the weather globally? And what exceptions to the rules might turn a trusty old proverb on its head?

Presenter: Anand Jagatia

Some people fall asleep almost as soon as their head touches the pillow, while for others it can take hours of tossing and turning. CrowdScience listener Assia needs at least 45 minutes to get to sleep: it's always taken her a long time to drift off no matter how tired she is, and nothing seems to make a difference. She asked us to investigate. 

Presenter Caroline Steel turns to experts to find out what happens in our bodies when we fall asleep, and why it’s more difficult for some than others. Eus van Someren explains how our bodies know when it’s time to get some rest and what can influence the difficulty of getting to sleep from our earliest years. Morten Kringelbach reveals that there may be more stages of sleep than we thought, and Ada Eban-Rothschild tells us why we have something to learn from the birds and the bees about getting a good night’s rest.

Caroline has trouble getting to sleep herself, and volunteers to have her sleep monitored in Cardiff University’s sleep lab. And we share some expert tips on falling asleep more easily.

Presenter: Caroline Steel 

With thanks to Professor Milton Mermikides for permission to include his composition ‘Transitions’.

(Photo: Caroline Steel takes a nap in Cardiff University’s sleep lab)

According to the United Nations Food and Agriculture Organisation, 800 million people are going to bed hungry every night, but 2 billion people in the world are malnourished. Farmers across the globe produce enough food to feed 10 billion people, yet there are only 7.6 billion of us.

We know there is enough food to go around, but filling tummies is only the start – we also need a varied diet. CrowdScience visits Nairobi during GGIAR Science Week, a hub for agricultural scientists. They are meeting to discuss the changes needed to get the right crops into the soil and the right food on the plates of those who need it.

Presenters Anand Jagatia and Alex Lathbridge are joined by a live audience and a panel of experts Lindiwe Sibanda, Sieglinde Snapp and Alex Awiti. Together they explore questions from our listeners in Kenya and around the world: whether we can restore natural habitats whilst promoting food security; why human waste isn’t used more commonly as a fertiliser; and what impact empowering women in agriculture will have on our ability to feed the world.

Recorded at CGIAR Science Week at the UN headquarters in Nairobi.

Image: Drone view of tractor ploughing a field

CrowdScience listener Sid is running late, and he’s turning to science to find an excuse. He and his partner Steffi in Singapore have very different attitudes to timekeeping. They wonder if this is down to their different cultural upbringings, or if they just had very different brains to start with.

Presenter Chhavi Sachdev puts her own time perception skills to the test to try to understand how subjective our sense of time can be. And we discover how the language we grow up speaking can influence the way we think about punctuality.

Presenter: Chhavi Sachdev

What would you discover inside the stomach of a sea lion? CrowdScience listener Robyn found out first-hand when she volunteered at her local museum in Adelaide, Australia. The team dissecting the specimen removed around 30 rocks from the animal’s stomach, and Robyn wants the Crowdscience team to find out how and why they got there.

Presenter Anand Jagatia uncovers a whole world of rock-munching creatures, from ostriches to ichthyosaurs. In search of answers we investigate Canadian sea lion research, and rummage through the vaults at the Natural History Museum in Bamberg, Germany.

Presented by Anand Jagatia

Image: Australian Sea Lion (Neophoca cinerea), Hopkins Island, South Australia

On the banks of the St Lawrence River in Quebec stands a 100-year-old lighthouse. While initially built to help boats navigate one of Canada’s most difficult waterways, the Point-de-Père site now also holds a different responsibility: it is a key reference for measuring sea levels around the entire North America continent.

But this is all set to change. With the development of new satellite technology, the tricky task of measuring sea levels is being updated - which could mean mountains around North America get brand new official heights.

In this episode we revisit a question from CrowdScience listener Beth, who wondered about the elevation signs she saw scattered along a mountainous road, indicating how high above sea level she was. As sea levels rise, will all the elevation signs need repainting? And how do you measure sea level, anyway?

The height of an enormous pile of rock like Ben Nevis, or Mount Everest feels unchangeable. But we measure them relative to the nearest patch of sea, which is where our story becomes complicated. Unlike water in a bath, sea level is not equal around the world. In fact, nothing on earth - not the sea, the shore or the mountains - is stable or constant, so the question of what you measure from and to becomes incredibly tricky. But that hasn’t stopped scientists risking life and fingers to use an ever-evolving array of technologies to find answers.

Join host Marnie Chesterton as she dives into the mechanics of the latest sea level technology, and how it could make a big difference to understanding our unpredictable world.

Presenter: Marnie Chesterton

(Image: Elevation Sign Post, Rocky Mountain National Park. Credit: Stephanie Beverungen via Getty Images.)

Host Anand Jagatia tackles gravity - a fundamental force of the universe yet also an everyday mystery that has baffled several listeners. Can you outrun it? Or at least use it to get fitter? If it varies, does that mean that you weigh less, depending on where on earth you stand? And if it’s the force of attraction between any objects with mass, are you technically more attractive after eating a massive cake?

Professor Claudia de Rham from Imperial College London explains the basics of gravity, while we discover the best place on earth to weight ourselves, with Professor Paddy Regan from Surrey University and NPL Fellow in Nuclear and Radiation Science and Metrology.

Anand takes a very fast spin on a special chair to experience extra gravity, thanks to Professor Floris Wuyts from the University of Antwerp, Kings College London and Minister of Science of Asgardia.

And finally, we talk to an expert lined up at the other end of a hypothetical hole through the earth: Professor Richard Easther from the University of Auckland, New Zealand. What would happen if we fell straight through the earth?

CrowdScience finds gravity a force to be reckoned with.

Presenter: Anand Jagatia

Are food allergies higher in the West than the East? UK-based listener Jude wants to know the answer. Her daughter-in-law Min didn’t know anyone with food allergies when she was growing up in South Korea and thinks that they’re not so common there.

Host Alex Lathbridge investigates. Along the way, he finds out what makes us sensitive to food allergies and how much that depends on our environment. He volunteers to have an allergy test, learns what triggers food allergies and tries to discover what lies behind their increase around the world.

Alex talks to some of the leading experts on food allergies in search for an answer to our listener’s question: Paul Turner breaks down what happens in our bodies when we have an allergic reaction; Jennifer Koplin explains why Australia tops the league table for food allergies and Michael Levin reveals what he found out in his ground-breaking research in South Africa comparing urban and rural populations. We also hear from Hana Ayoob, who grew up in Singapore and the UK, who describes what it’s like to suffer from multiple food allergies and describes the difference in cultural attitudes. Finally, we turn to Sooyoung Lee in South Korea to see if our listeners are right about the difference in rates for food allergies between East and West.

Presenter: Alex Lathbridge

(Image: Young Asian father with cute little daughter grocery shopping for dairy products in supermarket Credit: d3sign via Getty Images)

CrowdScience listener Alina is in a relationship with a polyamorous partner and is very happy with this arrangement, which got her thinking – why is monogamy so often the norm in human societies?

Presenter Caroline Steel goes on an anthropological odyssey to figure out where this drive to find a single partner - and stick with them - comes from.

What can science tell us about how human relationships developed, and whether having one or many partners is more 'natural'?

Evolutionary biologist Kit Opie of the University of Bristol joins us at London Zoo to help us understand the mating systems of our closest primate relatives.

To find out how polygamy developed in some parts of the world we speak to anthropologist Katie Starkweather of the University of Illinois Chicago.

And we learn about the chemistry of bonding from Sarah Blumenthal at Emory University, who explains how the brains of prairie voles may give us clue about the neurochemicals which shape human relationships.

Presenter: Caroline Steel

(Image: Dancing wedding cake figurines Credit: Peter Dazeley via Getty Images)