Ruth Alexander learns about ‘forever’ foods - stocks, soups and sourdough starters that can be replenished again and again and used for weeks, months or even years.

Ruth hears about a beef soup in Bangkok that has been maintained for 50 years, and she bakes a loaf of sourdough bread using a 69-year-old starter that has been kept going by Hobbs House Bakery in the south-west of England.

Cookbook writer Fuchsia Dunlop in London, UK, talks about the tradition of cooking with an ‘everlasting’ broth in Chinese cuisine.

Annie Ruewerda in New York in the US was charmed by the idea of a perpetual stew, she kept hers going for two months and it became an online hit – bringing hundreds of strangers to her local park to try the stew and add ingredients.

Lee-Ann Jaykus, distinguished professor emeritus and food microbiologist at North Carolina State University in the US explains the food safety rules you need to know if you want to try a perpetual dish at home.

Martha Carlin, distinguished professor of history at the University of Wisconsin-Milwaukee in the US helps unravel the claimed historical origins of perpetual stew.

And our thanks to World Service listeners David Shirley and Mark Wood for telling us about the oldest dishes they have eaten.

Producer: Rumella Dasgupta and Beatrice Pickup

(Photo: A huge pot of beef soup in that has been added to over 50 years at a restaurant in Bangkok, Thailand. Credit: David Shirley/BBC)