Grinding Coffee

The single most important variable in brewing coffee is uniform particle size.  The more uniform the particle size the more uniform the extraction process. Whether the brewing apparatus is the drip brewer or the French press the ideal brew should contain a large amount of the desired flavoring compounds and the least amount of the unwanted flavoring compounds. 

In the late 1940’s the coffee industry adopted a set of grind standard designations in an effort to classify the ground coffee into groups that would produce acceptable results.  The intent was to determine what particle size distribution brewed the best coffee in different types of coffee brewing equipment.  The classifications were named regular, drip and fine.  Since the grinding of coffee produces a range of particle sizes extensive test were performed to determine what range of particle sizes would produce satisfactory results in each type of brewer.  A set of sieves sizes were selected and a test procedure developed to determine the particle size distribution.  The table below shows the classifications used today.

Not all coffee grinders are alike.  Some grind coffee with a narrow range of particle size and some produce coffee particles with a broad range.  There are three types of coffee grinders used today, the burr grinder, blade grinder and the roller grinder.  

 

Burr Grinder:

The preferred method of grinding coffee is the burr grinder.   The burr grinder can be further divided into the disc and the conical burr grinder design.  The disc grinder burrs are constructed of two nearly flat discs and the conical design constructed more like two tapered cylinders nested inside each other like two stacked paper cups.  The discs or cones have serrated teeth to shear the coffee cleanly.  The cutting surfaces are spaced precisely to produce the particle size desired and have a means of adjusting this spacing to change the particle size.   A well designed burr grinder will produce a relatively narrow particle size distribution resulting in uniform extraction during brewing. 

There are a number of varieties of burr grinders on the market today.  Since coffee is susceptible to an annoying static charge buildup during grinding the slower rotating grinder models tend to reduce the charge buildup.  Heat generated during the grinding process is detrimental to the coffee and should be avoided.  To reduce these two adverse effects the higher priced grinders will employ a gear box or speed reducer.

 

Blade Grinder:

The blade grinder is nothing more than a small food processor utilizing a spinning blade inside a small bowl covered by a lid.  There are no adjustments in this type of grinder and the resulting ground coffee size distribution is large.  The result will be fine particles mixed in with large shredded pieces and all the other sizes in-between.  While they are the least expensive type available they also produce the least control over the ground coffee particle size.

 

Roll Grinder:

The roll grinder is exclusively limited to the large coffee roasters where high volume is needed.  These grinders are constructed of two rotating rollers precisely spaced.  The rolls have a corrugated pattern of specially designed cutting edges that grinds the coffee as they pass through.   

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