Coffee sorting

The green coffee obtained after seed extraction must undergo a sorting process carried out by specialists in the country of production: each bean is examined and small portions of each type of coffee are often roasted and tasted to define its quality. This will determine the market price.

For obvious reasons, this phase involves all players in the coffee marketing chain: coffee wholesalers, coffee distributors and suppliers to cafés, dealers, café owners, and those who have opened stores that sell coffee pods and capsules.

Let’s take a closer look at the phases of this delicate stage.

How coffee is selected

Once the seed has been extracted, the beans can be sorted either manually or mechanically (e.g. by means of an optical lens that identifies the colour differences between one bean and another) in order to discard overripe beans or those that are about to ferment.

At this point, the coffee is classified according to various characteristics:

1) Producing country, region or port of shipment

2) Processing method

3) Year of harvest

4) Botanical species (Arabica or Robusta)

5) Number of defects or impurities

6) Shape and thickness of the beans

7) Colour

8) Organoleptic properties (usually indicated only on Brazilian coffee packs)

The most important criteria for sorting is the shape and size of coffee beans.

The assumption is that coffee plants grown at high altitudes produce larger beans than those grown at lower altitudes. Coffee grown at high altitudes has a slower ripening time and develops a more subtle and refined aroma, so it is generally believed that the larger the bean size, the better the coffee quality.

In reality, this size/quality ratio is not entirely reliable and has too many exceptions; therefore, the sorting criteria concerning size is used to assess whether coffee batches are homogeneous and allows even and consistent roasting of all beans.

Over time, a method has emerged that is not based on strictly scientific criteria, which, however, is very effective in classifying bean size: it involves the use of sieves,with holes of increasingly smaller diameter, varying from one sieve to another. When passing through the various sieves, the beans slide between the holes until they find a hole that they cannot pass through: that will be the sieve size required, expressed as one sixty-fourth of an inch.

Technically speaking, the sieve hole sizes are reported as 17/18, 15/16 that corresponds to 17/64 of an inch, 18/64 of an inch, and so on.

A classification based on degrees can also be made, which takes into account the size of the holes in millimetres:

–       Grade 0: the beans are retained by sieve No. 18, with 7 mm holes

–       Grade I: the beans pass through sieve No. 18, but are retained by No. 16, with 6.3 mm holes

–       Grade II: the beans pass through No. 16, but are retained by No. 14, with 5.5 mm holes

–       Grade III: the beans pass through No. 14 and are retained by No. 12 (4.7 mm holes)

–       Grade IV: the beans pass through No. 12 and are retained by No. 10, with 4 mm holes

Different sorting methods are applied to coffee grown in various parts of the world. For example, Brazilian coffees, the most popular worldwide, are classified according to the “New York” system, i.e. the sieve system.

In Africa, the classification is by letter (AA, AB, etc.). The AA parameter, i.e. a coffee classification term, refers to a size above sieve No. 16.

There is more than one method for sorting coffee beans on the basis of the defects and impurities they contain, but the most important one is defined by the New York Coffee and Sugar Exchange. This institution was originally founded by coffee merchants as the Coffee Exchange in 1882 and, over the years, it included the exchange of sugar, cocoa and cotton until it became the New York Board of Trade (NYBOT).

The New York and Sugar Exchange method involves analysing a sample of two-thirds of a pound (approximately 300 grams of coffee), in which defective beans and impurities are counted on the basis of two different parameters: intrinsic defects of the beans and defects due to foreign bodies. Each defect is given a different score.

For example, each black bean (intrinsic defect) is worth one point, whereas a stone or twig found in the sample is worth five points (defect due to foreign bodies).

Once the scores have been assigned to the sample, it is given a sorting grade on a scale from zero to six. Zero ideally indicates perfect coffee, whereas six is for the worst coffee.