After milling, green coffee is graded and classified for export. The aim is to produce homogenous commercial lots that meet defined quality criteria, and hence facilitate a fair system of pricing. However, there is no universally accepted grading and classification system for green coffee. Each producing country has developed its own classification and grade charts, which are often also used to set minimum standards for export.

Strictly speaking, grade indicators are used to describe the size of the bean and are commonly expressed in 1/64 of inch. E.g.beans of grade 18 will pass through screen 18 (holes with a diameter of 18/64″), but are retained by screen 16/17. The theory behind classification based on bean size is that coffees of the highest altitudes are more dense and larger in size than those produced at lower altitudes. Similarly, coffees develop more slowly at higher altitudes and often have the best flavour profiles. The size and size distribution of beans also has an impact on optimisation of roasting conditions.

There would thus appear to be a loose correlation between size, density, and sensory quality. However, this correlation has numerous exceptions, and size classification should only be used to verify that the coffee lot in question is uniform in size – which helps ensure a uniform roast.

In reality, grading and classification systems are usually based on some, or all, of the following criteria. Invariably this means that most systems are often very detailed and diverse, and open to confusion and mis-interpretation regarding the ‘transferability’ of certain descriptions and terminologies between producing countries: