Kokoda Coffee

Hulled green bean is now ready to be graded. 
Before we go on, we must point out that, normally, when someone is selling an "A Grade" coffee, they are usually trying to let the customer know that the coffee is of excellent quality.
The problem is, unfortunately, most roasters have not been trained, worked on or even seen a coffee production operation. Normally, a properly produced coffee anywhere in the world should be given two grades, not just one.  The first grade should denote the quality that the coffee is sorted to, in terms of defect count per kilo.  The second grade should denote the physical size of the beans which are sorted to the quality specified in the first grade. These grades are very important, as we will explain below.

In Papua New Guinea, green bean coffee is graded according to physical size.  Once the sizes have been separated, the coffee is then graded for quality, within those sizes.  Ungraded green bean coffee is not uniform in size or colour as it is a raw product.  First, you must separate the coffee into different physical sizes of beans.  This is done in a machine called a linear sorter.  The different sizes are defined by varying "screens", which are like big sieves. Basically, the machine features a stack of the different screens on top of each other in layers.  The largest screen (biggest holes) is at the top, and the smallest is at the bottom.  The green bean to be graded is fed into the machine from the top.  Each screen layer has progressively smaller holes, going from top to bottom.  Each screen layer is independently agitated.  The agitation cause the beans to vibrate on each sieve, and the beans which are small enough to fall through the holes in that particular layer go through, while the beans that are too big stay, and are fed into separate bags for additional grading later.  

This is where the first grading of a coffee comes from - the size of the beans.  The grades used for coffee from Papua New Guinean are as follows:

Grade                                 Screen Size
AA                                       18 and above
A                                         17
X                                         15-16
Ax                                        Bigger than 14, but smaller than 17
T                                         Triage.  T grade coffee is not graded according to size, or quality.

This is where the "A" in "A Grade" coffee should come from - the size of the beans, NOT the quality of the coffee.

A note on T grade coffee 
T grade, or Triage coffee as we call it in the industry, is basically the defect coffee that is removed from other grades of coffee.  There are no specifications as to the size of the beans.  The only requirement for T grade is that it must contain at least 60% whole beans.  A bag of T grade coffee can be made up of entirely defective coffee beans (not a green bean in sight), but at least 60% of those beans must be full beans, and not cracked or broken.  T grade coffee is sold to many of the big companies who produce instant coffees. 

A note on Ax grade coffee
Ax grade coffee is virtually ungraded according to size.  The only limitations are that the very large and the very small beans are not included (bigger than screen size 14, but smaller than size 17).  Ax coffees are very bad for roasting because the sizes of the beans are not uniform.  When roasting, the smaller beans will cook much faster than the larger beans resulting in an uneven roast and unpredictable flavour.

Green bean grading machinery in a factory in Papa New Guinea

Once the beans have been graded according to size, they must be sorted according to density.  A good coffee bean will be denser than a bad one.  The coffee is fed into a machine called a Densometric sorter.  This machine sorts the coffee using its density, or weight.  The heavier, good coffee is fed out one end, and the lighter bad coffee out the other end.  This less dense coffee is usually added to T grade or Ax grade coffee to add bulk.

The good green bean is now ready for Sorting to remove defects.  Click here or use the menu to the left to continue the Journey of Coffee.