In 1819 an ambitious young Austrian music publisher named Anton Diabelli sent Austria's premier composers a vivacious waltz he had written and asked them to contribute one variation each on the theme. Over the next several years some 50 complied. Beethoven was the most eminent invitee (Liszt was among them, too; he contributed the 24th variation at the age of 11). Variations to Beethoven were like potato chips to us—he couldn't write just one. So he wrote 33. And they ain't potato chips. Along with Bach's Goldberg Variations, the Diabellis are considered among the greatest ever written; there are certainly more of them. One of the charming things about the Diabellis is their humor and puckishness, even though they were written toward the end of the composer's life when he was quite deaf and laboring simultaneously over such exalted works as the last three piano sonatas. Anton Schindler, Beethoven's close friend, called the Diabellis "a work bubbling with a singular sense of fun," and that is precisely what Daniel Barenboim delivers. He takes the opening theme at a Keystone Kops pace—startling at first, but not out of line. In the hour of music that follows, with its extreme shifts of mood and texture, Barenboim plays with great expressivity, ranging easily from the pitter-patter delicacy of the second variation to the dizzy, heavy-soled cavorting of the 21st. Peter Serkin, by contrast, seems to have taken his cues primarily from the more solemn elements in the work. He brings somewhat less gusto to the Diabellis than Barenboim, and some of the middle variations bog down a little as a result. He has his moments—the comic 22nd for instance—but Barenboim's version has the character to stand alongside Alfred Brendel's 1977 recording, the best Diabellis of recent vintage.