BERLIN, Germany (AP) -- Experts have discovered a previously unknown work by Johann Sebastian Bach in documents taken from a German library shortly before it was heavily damaged by fire, researchers said Wednesday.
It was believed to be the first new Bach work to surface in 30 years.
Researcher Michael Maul found the aria, dated October 1713, in May in the eastern city of Weimar, the Bach Archiv foundation said on its Web site.
There was no doubt about the authenticity of the handwritten, two-page score, the Leipzig-based foundation said.
Maul said it was the first Bach work to come to light since 1975, when a copy of the "Goldberg Variations" in a private collection was found to contain extra canons for piano in the composer's own handwriting. The last previously unknown vocal work by Bach to surface was in 1935, when the single-movement cantata fragment "Bekennen will ich seinen Namen" was discovered, the foundation said.
"The find is a well-rounded composition -- not a major work, but a casual piece of superior quality," the foundation said of the aria.
The foundation's director, Christoph Wolff, said the work, written when Bach was 28, was among documents taken from the Duchess Anna Amalia library for restoration before September's fire.
"Otherwise the work would have been consumed by the flames and we would never have known of its existence," Wolff said.
The library, housed in a 16th-century rococo palace, reopened in February.
Bach composed the work for a soprano, to be accompanied by strings or a harpsichord, to mark the 52nd birthday of the duke of Saxony-Weimar, for whom he worked as a court organist, the foundation said.
A solo soprano was to sing a 12-verse poem beginning with the duke's motto "Everything with God and nothing without him" written by Johann Anton Mylius, it said.
The work was Bach's only known strophic aria, in which several stanzas are set to the same music, and the precise date made it valuable to researchers studying the development of the German composer's style, the foundation said.
It was not clear if it was played at the time, but the foundation said English conductor Sir John Eliot Gardiner is preparing to record it.
Gardiner last month received a medal in recognition of his performance of Bach music from the Saxony city of Leipzig, where Bach was cantor of St. Thomas Church for 27 years.
Germany's Baerenreiter publishing house plans to publish the composition in the fall.