If we are to take the Noontime Concerts™ epithet of “San Francisco’s Musical Lunch Break” literally, then today’s recital by pianist Peter Grunberg served up a healthy slab of variations by the young Johannes Brahms between generous slices of two of Ludwig van Beethoven’s tastier sonatas, Opus 79 in G major and Opus 81a in E-flat major, two of the three sonatas he composed in 1809 (the third being Opus 78 in F-sharp minor). As is the case with any well-made sandwich, the bread stood on its own merits as well as complementing the interior. However, we also had the contrast of Brahms, in his mid-twenties beginning to make a name for himself in the wake of the death of Robert Schumann, with Beethoven, beginning to push forty and having completed his final piano concerto (Opus 73 in E-flat major, best known as “Emperor” and just performed in Davies Symphony Hall at the end of last month). Indeed, as I suggested in writing about that concert, Opus 73 abounds with good-natured spirits; and many of them seem to have spilled over into the two sonatas that Grunberg selected…