It's likely you're thinking of Festering Coffee from the "The Book of Ages" quest on Neopets. This quest is part of the "The Book of Ages" plotline that revolves around finding the pieces of the titular book to save Neopia.
You can find Festering Coffee as a quest item during the "The Book of Ages" quest line. It's a key ingredient to make the "Coffee of Ages".
To find the Festering Coffee, you'll need to follow the instructions given in the quest. It involves searching for a specific location on Neopets, interacting with certain characters, and completing certain tasks.
Remember, Festering Coffee is not a permanent item on Neopets. It's a quest item that's only available during the "The Book of Ages" quest.