From New Babbage Department of Records and Archives
Blackberry-like fruit growing on thorny vines outside of the city wall.
If prevailing winds flow in a certain direction during the spring, they carry ash and cinders from New Babbage factories and foundries that are then deposited on soil where the berries grow just outside the Palisades gate.
The mineral content of the debris is absorbed by the root network of the plant and results in a woody flavor with slightly metallic undertones. The taste isn't unpleasant, and it isn't poisonous (that we are aware). Given the unique mix of industries in New Babbage and the content of the air and soil, nothing like it grows elsewhere in the world.
Reputed to be delicious when eaten with sugar and groats in a bit of vole milk.
Cinderberries should always be used right away or dried for storage. They are unsuitable for mead fermentation due to potential toxins which can be released during the rotting process.
Reference: A Trip with the Builders