The grinder is an extremely important piece of your espresso bar. Commercial espresso grinders work by pulverizing the beans between two heavy conical burrs. To achieve proper espresso extraction, the barista adjusts how far apart the burrs sit to change the grind size (more coarse or more fine). A good grinder will provide consistency and reliability. In a commercial setting, plan on two espresso grinders at least. One for your regular blend, one for decaf, and maybe a third one for a special third blend or single origin espresso.