Overview: Sian Williams and Stefan Gates lift the lid on the food that goes into the annual festive feast. Stefan visits a turkey farm to investigate the reason for the price difference for a basic white turkey, at around £20, and a Norfolk Black, which can cost £75. Sian discovers how the bitter taste is being bred out of sprouts and there's a report on mince pies, revealing how the most expensive may not be the best tasting. Plus, why do people fall asleep after eating Christmas dinner?