Opening Friday: Summer feels a bit tentative this year, but the Minnesota Orchestra's 32nd Sommerfest is right on schedule. For the obligatory Viennese opener, artistic director Andrew Litton has assembled bonbons by three members of the Strauss family, not excluding Johann II's "On the Beautiful Blue Danube" -- perhaps the most successful piece of pop music ever written. Salting the Strausses is a Hardanger (Norwegian folk) fiddle concerto by Geirr Tveitt, with soloist Ragnhild Hemsing, and an as-yet undetermined piano concerto movement, played by the winner of the 2011 e-Piano Junior Competition (to be announced earlier that day).