Gregg Wallace discovers how one of Britain's largest bakeries makes up to one and a half million loaves of bread each week. Following the production of one of the nation's favourite loaves, he uncovers the secrets to baking four thousand loaves at once and reveals the incredible machine that can bag a loaf of bread in midair. Cherry Healey goes inside one of the largest flour mills in the country to discover what it takes to make the perfect flour.