Schplict was the milk from a grakel.

In 2371, Neelix acquired some schplict on the planet Napinne which he used to make brill cheese after receiving a request for macaroni and cheese by Ensign Ashmore. But the bacteria he cultivated for the cheese became host to an infectious virus that spread throughout USS Voyager. In effect, the bio-neural gel packs in every system became "sick". (VOY: "Learning Curve")