John Steinbeck’s classic novel, The Grapes of Wrath, might not seem like the best libretto for an opera. For one thing, it’s awfully long. For another, destitute Dust Bowl denizens singing in grand operatic style? Seems a bit much. But the opera, which gets its premiere this weekend in Minnesota, is intended as “a work that will bring new audiences for an art form long thought of as irrelevant by American audiences – if they’ve even thought of it at all.”