A spongy collection of flour, water, wild yeasts and bacteria may seem an unlikely object of affection, but some sourdough starters are truly cherished, and can even become part of the family. Emily Thomas hears how one starter has been used to bake bread in the same family since the Canadian gold rush more than 120 years ago, and speaks to a man trying to preserve sourdough diversity and heritage by running the world's only library dedicated to starter cultures. And a German baker, whose starter has survived Nazism and communism, reveals the commercial demands of maintaining it and why old ‘mothers’ (as sourdough starters are known) hold a powerful lesson for us all in nurturing living things. Producers: Simon Tulett and Sarah Stolarz (Picture: A woman holding bread. Credit: Getty Images/BBC) Contributors: Ione Christensen; Karl de Smedt, Puratos; Christoph Hatscher, Bäckerei & Konditorei Hatscher