Coffee into theorems The late mathematician P. Erdös has often been associated with the observation that "a mathematician is a machine for converting coffee into theorems" (e.g., Hoffman 1998, p. 7). However, this characterization appears to be due to his friend, Alfred Rényi (MacTutor, Malkevitch). This thought was developed further by Erdös' friend and Hungarian mathematician Paul Turán), who suggested that weak coffee was suitable "only for lemmas" (MacTutor, Malkevitch).
From http://mathworld.wolfram.com/Theorem.html