PASTICCIO is an Italian word for pie or pudding; it can also mean a jumble or a mess. Operettas employing preexisting music were not uncommon (e.g., The Beggar's Opera), but the fashion for the operetta-pasticcio based on one composer did not really take hold until this century.
Wiener Blut (Carltheater, 26 October 1899), concocted from Strauss compositions by Adolf Müller, Jr., to a text by Viktor Léon and Leo Stein, was ordered by the Carltheater's manager Franz Jauner. Léon was Jauner's head director at the Carltheater; with Stein he wrote a rather ordinary, sentimental romance of mistaken identities, set at the time of the Congress of Vienna (1814-15). Strauss wanted to arrange the melodies from his old compositions (and presumably orchestrate them) but was too infirm. It was suggested that Müller, the house composer and conductor at the Theater an der Wien, do the task. Strauss was agreeable, but a few months before the première, Strauss was dead. The waltz-king and his century had gone.
In fact, Wiener Blut has not too much to do with the Congress of Vienna or its principals; the story might well have taken place at any other time. (Erik Charell's 1931 film, Der Kongress tanzt, was the definitive operetta depiction of this period.) There is a certain Viennese flavor to the character names, the dialogue, and, of course, the prior association of so much of Strauss's music to Vienna itself. The première was an almost complete fiasco and Wiener Blut barely managed to stay on the boards a month, after which it was hastily transferred to the Raimundtheater. In 1905, a revival with a rearranged book at the Theater an der Wien was unaccountably a huge success, and the pasticcio appeared at the Volksoper in 1928, where it has reappeared ever since.