A trip to California reveals the secret of perfect walnuts. Plus, what makes sour sweets sour? And how do brewers make their trendy hazy beers cloudy?

A trip through the show's archives, looking back at some favourite chocolate-based investigations, including Jimmy Doherty on the trail of how bubbles end up in bubbly chocolate. Matt Tebbutt heads to one of the UK's largest chocolate factories to find out what makes white chocolate white and gets the inside story on the UK's best-selling after-dinner mint, while Kate Quilton heads to Ghana to uncover the truth behind reports that dark chocolate can be good for your health.