Kate Quilton finds out if there is any difference between soft and crusty bread rolls, and Andi Oliver reveals why chocolate chips don't melt when baked in cookies. Andi also asks why pre-made sandwiches always seem to have mayonnaise in them, Matt Tebbutt uncovers some of the secrets of ready meals and Briony May Williams discovers the surprising science of how canned food can last so long.

Jimmy Doherty and Matt Tebbutt embark on an extraordinary road trip through America's Deep South. Starting on the Gulf Coast, in New Orleans, they discover how the shells from the huge number of oysters consumed locally could protect the coastline. Heading through Mississippi, Jimmy and Matt find out what makes southern sweet tea different from a British cuppa. In Alabama, Matt wants to know why they fry green tomatoes, and Jimmy uncovers exactly what grits are. Then it's off to Tennessee to visit the Jack Daniels distillery and discover the secrets of sour mash. In Louisville, where the South meets the North, Jimmy and Matt learn about fast-food consistency at Kentucky Fried Chicken HQ.