The Espresso machine and its proper settings of temperature range, pressure profile curve, and water quality and shot volume.
The grinder or coffee mill, and its proper settings of how fine or coarse, dosing volume of the grounds, and burr sharpness.
The specific recipe or blend of beans that the bar will employ - it's signature flavor style.
The hand that prepares. The conductor of the symphony is the final arbiter of whether a prepared coffee has passed every quality step and deemed worthy to be presented to a guest in the café.