A whole lot of work goes into hand sorting specialty coffee. You wouldn't believe the kind of green bean coffee defects that make their way into substandard coffees. Specialty coffee is all about minimizing defects so that you can taste the real flavor characteristics of your coffee. The low standard coffees that you will find in a can (and often also a bag) at your supermarket are full of these defects. I recently took some close up pictures of some common defects found in green coffee beans:
The SCAA (Specialty Coffee Association of America) has specific standards for grading coffee beans:
Specialty Grade Green Coffee (1): Specialty green coffee beans have no more than 5 full defects in 300 grams of coffee. No primary defects are allowed. A maximum of 5% above or below screen size indicated is tolerated. Specialty coffee m ust possess at least one distinctive attribute in the body, flavor, aroma, or acidity. Must be free of faults and taints. No quakers are permitted. Moisture content is between 9-13%.
Premium Coffee Grade (2): Premium coffee must have no more than 8 full defects in 300 grams. Primary defects are permitted. A maximum of 5% above or below screen size indicated is tolerated. Must possess at least one distinctive attribute in the body, flavor, aroma, or acidity. Must be free of faults and may contain only 3 quakers. Moisture content is between 9-13%.
Exchange Coffee Grade (3): Exchange grade coffee must have no more than 9-23 full defects in 300 grams. It must be 50% by weight above screen size 15 with no more than 5% of screen size below 14. No cup faults are permitted and a maximum of 5 quakers are allowed. Moisture content is between 9-13%.
Below Standard Coffee Grade (4): 24-86 defects in 300 grams.
Off Grade Coffee (5): More than 86 defects in 300 grams.
Grading Information from coffeeresearch.org - For more info I highly recommend checking out their website and the SCAA website.