His contributions include studies on the Agaricales (gilled mushrooms), especially the genus Russula, about which he wrote a monograph in 1933.
[2] Later, he revised the genus in the series Die Pilze Mitteleuropas (1926–1967); his notes were published posthumously by his wife Liesel in 1952 with the help of other mycologists.
The work was considered the "authoritative treatment of the group for Central Europe".
[5] Schäffer is the only mycologist of modern times known to have died from consuming poisonous mushrooms, in this case, Paxillus involutus.
About an hour after he and his wife had eaten a meal prepared with the mushrooms, Schäffer developed vomiting, diarrhea, and fever.