The correct type of grinder is needed to achieve the proper espresso grind. For example, home type blade grinders are incapable of grinding the coffee fine enough which will result in under extraction. Commercial type burr grinders where the coffee is ground between two textured plates is the type of grinder most preferred by espresso bars. This grinder holds the whole beans in a top hopper where they are fed through the adjustable burrs depositing the ground coffee into a secondary dispensing unit called the doser. There is a feature on most grinders that allows you to stop the flow of beans into the grinding mechanism should the top hopper need to be removed before it is empty.
The grinder itself is a fairly simple piece of machinery an on off switch is usually located near the base of the unit on one side. The most important feature to be aware of is the grind adjustment control. A good Barista may have to adjust the grind many times daily. The grind may be affected by humidity, temperature and other weather factors present. The proper grind should always be determined by timing the extraction.
