By Beethoven 's time , B minor had changed in people 's minds : Francesco Galeazzi wrote that B minor was not suitable for music in good taste , and Beethoven labeled a B minor melodic idea in one of his sketchbooks as a `` black key '' . By Beethoven 's time , however , the perception of B minor had changed considerably : Francesco Galeazzi wrote that B minor was not suitable for music in good taste , and Beethoven labeled a B minor melodic idea in one of his sketchbooks as a `` black key '' .