Gregg Wallace explores the secrets of the Guinness brewery in Dublin to reveal how it makes two million litres of Irish stout every single day.Cherry Healey visits a water treatment centre to learn how reservoir water is treated to provide clean drinking water to the people of Dublin, as well as to the stout brewery. And she visits a farm in Worcestershire to help with the hop harvest.Historian Ruth Goodman delves into the history of Irish pubs and explores the extraordinary story of how pub games helped the Allies in the Second World War.