Andi Oliver meets cookery writer, presenter and GBBO star Briony May Williams to sample her home-made soda bread. Briony makes soda bread just as her incredible Granky did, using a recipe that's now over 100 years old. Andi and Briony wonder how on earth anyone discovered that using ash from a fire makes a delicious risen loaf, get stuck into the science of acidulation and saccharomyces cerevisiae, and Andi has a bread-related brainwave which will transform the way you roast a chicken and will quite possibly change your life. Food Scientist: Kimberley Wilson Food Historian: Neil Buttery Producers: Victoria Lloyd and Lyndsay Fenner Series Producer: Lucy Dearlove Exec Producer: Hannah Marshall A Storyglass production for BBC Radio 4