Mr. Doherty's mission to unravel the scientific secrets behind mass food production continues with an investigation into the contents of sandwiches. Why does supermarket bread stay soft longer than home-baked bread? Jimmy attempts to recreate some "supermarket bread", building his own factory mixer from a metal dustbin. He also wonders what it is about processed cheese slices that people love so much - after all, they're only 60 per cent cheese. Could it simply be that they're sliced-bread shaped? Back in the barn, Jimmy sets up his own processed-cheese production line to find out what the other ingredients are. That's not all, bugs and caterpillars are rarely found in ready-bagged supermarket salad leaves, so he investigates how one Wiltshire producer checks that 1.5 million bags a week are bug-free. Jimmy is also keen to discover how supermarket suppliers grow tomatoes out of season, and wonders whether they are doing anything to the fruit to be concerned about.