2 of 5 added 9 characters in body

ß isn't beta. It's the (german) sharp s. The greek beta looks like this: β.

The fastest method probably is:

  • enable the greek keyboard layout permamently in System Preferences -> Keyboard -> Input Sources
  • defining and enabling a free keyboard shortcut in System Preferences -> Keyboard -> Shortcuts -> Input Sources -> Select next source in input menu (e.g ShiftAltSpacebar)

To type α/β/γ/ε etc., you just have to switch the keyboard layout with ShiftAltSpacebar, hit A/B/G/E etc. and switch back to your common keyboard layout with ShiftAltSpacebar.