The manuscript of the 1789 work, found in the British Museum, contains only the composer's rough outline of themes for the movement, but it has been made into an eight-minute work by Cees Nieuwenhuizen, a Dutch musicologist.
Conrad van Alphen, artistic director of the Rotterdam Chamber Orchestra, said, "As far as we know, Beethoven did write a whole concerto that included this Adagio and disappeared. We have not found any trace that it was ever played before."
The piece is consistent with other works from early in the composer's career, van Alphen said: "The atmosphere of this piece is very close to that of the Third Piano Concerto."
British pianist Ronald Brautigam will perform the work at De Doelen, a concert hall in Rotterdam, on February 1, and then reprise the program three other Dutch cities. He will play in Kampen on February 3, in Hengelo on February 12, and in Hoofddorp on February 13.