How are coffee beans sorted in a selective roastery?

Why should we sort coffee beans?

When reading about choice coffee, you will often learn that coffee beans must go through a sorting process. But what does that mean?

According to the Select Coffee Association, it's a standardized method of comparing coffee beans that assesses the relationship between the amount of defective beans and the overall quality of the cup.

Not all coffee beans are the same, some are underdeveloped, small, broken or even defective. If you've ever wondered why your coffee tastes unpleasant, it may be due to the roasting and processing process.

Having a defective coffee bean is like eating a handful of peanuts and discovering that there was one burnt in that handful. One bean can ruin the overall taste of your cup.

Coffee grading methods

Grading green beans starts with hand picking the beans, where they are selected according to their quality, which can be identified by their visual appearance and density (whether the beans float on water).

Sorting and picking is the last step in the processing of coffee beans and is carried out either manually or mechanically. Typically, coffee beans are sortedfirst just by size and then by thickness.

Manual sorting of coffee beans

For most high-quality coffees, sorting is done in the simplest possible way - by hand. The best coffees can be hand-cleaned twice (double picking) or even three times (triple picking). Hand-cleaned coffee is usually called European preparation.

Mechanical sorting of coffee beans

Machines today can mimic the human eye and hand. Streams of beans fall into the machine quickly, one by one, past sensors set according to parameters that identify defective beans by shape or colour.

The machines can easily detect any immature, discoloured, sour or insect-damaged grains left after processing. The moment the machine detects a defect, it ejects the damaged grain from the stream of healthy grains using compressed air.

Coffee bean defects

After harvesting, coffee beans may haveseveral defects that can affect the final taste and quality. Here, those defective beans are carefully selected and removed before roasting, so they don't make it into the selection pack and you won't feel it in the final taste of your cup.

According to the classification standard for coffee beans SCAA , one of the best coffee beans we drink most often is specialty grade coffee, which includes beans of only the best quality. These beans must be free of primary defects and have no more than 5 full defects in 300 grams of coffee.

When cupping these beans must have a distinctive characteristic in one of the areas of flavour, acidity, body or aroma.

Unroasted beans

As you might guess from the name, unroasted beans are under-roasted and therefore still partially green.

Visually, they may be light in colour or, in extreme cases, even have a green tint. They most often appear in light roasted coffees where the roasting process has been stopped too early.

Over-roasted beans

Simply put: over-roasting occurs when coffee beans are roasted for too long.

Overly developed beans have a smoky and ashy taste and are extremely dark in colour and oily. Some over-roasted beans taste burnt and bitter regardless of the preparation method.

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Immature coffee beans that are unfortunately hard to spot during roasting because they look very similar to mature coffee beans.

The best way to recognize them is by their taste, which will be dry and papery

Burnt coffee beans

If the roaster raises the temperature too quickly, it can literally burn the beans. Dark, burnt spots will appear on the flat parts of the surface of the coffee beans.

Usually, the burnt beans are few and quality roasters remove them before packaging.


Causes the same kind of taste and visual defects as burnt beans, but for a slightly different reason.

The visual differencelies in the location of the burn marks. While burn marks are on the flat surface of the grain, tipping marks are on the tips or edges.

Because coffee beans do not grow uniformly, defects can occur in each batch. What is important is whether the roaster takes the time to adjust their processes and remove defective beans before packaging and selling them.