How Processing Methods of Coffee Beans affect Coffee Quality & Roasting
Once picked, how the green coffee beans are prepared and processed can have a dramatic effect on coffee flavor as well as roasting effectiveness. And preserving the subtle, intense cup quality of specialty coffee beans requires processing steps far beyond the simple hulling and drying needed to prepare other coffees, seeds and grains for their markets. These extra steps, directed by expert quality management, add significant expense and value to premium specialty coffee beans.
Before they can be roasted, green coffee beans must be separated from the moist, sweet cherry pulp and inner hulls, then cleaned and dried. This series of steps is known as processing or preparation (prep). The main processing methods are known as: natural (dry), washed and semi-washed.
Natural or Dry Processing
This is the traditional way of preparing coffee beans for market and is the preferred method for many origins, especially where water is at a premium. At its most basic, ripe cherries are spread on the ground in the sun. When the fruit is dry, it is pounded and winnowed to separate the beans away from the dried fruit and hulls. They are then graded, weighed and bagged.
In terms of appearance, the presence of fruit pulp during drying and the pounding during cleaning mean that Natural Processed beans are pretty varied in color and shape. Many technical quality improvements have been incorporated to prepare Naturals for the specialty market – drying patios of gravel/cement instead of earth, or elevated racks to facilitate quicker drying. Also, specialized machinery is now commonly used to hull, separate and clean the dried beans. The result is cleaner cupping and with beans that have a more consistent appearance.
In the cup, Natural Processed coffees exhibit heavier body and flavor profiles with deeper-toned and more varied fruit, chocolate, spice and savory notes than the same beans prepared by the washed method. These coffees add depth and authority when used in coffee blends. But on the down side, Natural Processed coffees tend to have more chaff when roasting.
Washed or Wet Processing
Wet processing of coffee beans developed during the Industrial Revolution to facilitate advances in technology. It improved physical consistency, cleanliness and appearance of the green coffee bean. However it also requires abundant water resources and was pioneered in the tropical uplands of the New World.
Washed processing has 2 stages. The first “wet milling” stage starts with several washing and brushing cycles to separate the sweet pulp completely from the hull encasing coffee beans known as `parchment’. Next, the cleaned parchment soaks in concrete pools for several hours, allowing chemical changes that develop beans with very clean and bright flavor profiles. They are then dried; either by the sun on cement patios, or mechanically in huge rotating heaters called gardiolas.
In the second “dry milling” stage, the beans pass through a series of machines: they’re hulled and de-chaffed; graded by high-speed sorters to regularize size, color and/or density; then weighed, bagged and marked for shipping. The extremely consistent size, shape, color and flavor of beans processed by the washed method facilitates larger batch sizes and longer, darker roasting with less fire danger.
In the cup, washed coffees exhibit bright, clean flavor and aroma, with notes of fruit, citrus, floral and spice. Flavor is mainly perceived from tongue-tip through mid-mouth and up into the sinuses. Washed coffees have light to medium-heavy body, and provide a blend’s crisp, vital first impression.
Semi-dry or Semi-Washed Processing
This is a hybrid process between Natural processing and Washed. It is often used in Indonesia, Brazil and other origins with abundant water. It has some advantages in flavor and physical consistency over purely Natural processed coffee beans. It is used mainly for premium specialty-grade Specialty-grade beans due to its higher expense.
The process begins with removal of the outer cherry using wet pulping machines. The beans, still coated with sweet pulp, are “rested” – cured for up to a day – to develop the characteristic flavor profile of Naturally processed coffee beans. The pulp is again rinsed and the parchment coffee, still with traces of pulp, is fully sun-dried. Grading, weighing and bagging is accomplished in mechanized dry mills, similar to those used in wet processing.
By gently removing most of the fruit before drying, controlling the amount of pulp contact during drying, and then using mechanized dry milling, the coffee flavor, and especially its physical consistency, is greatly improved. The beans retain the same flavor and body as Natural process coffees.
More on Green Coffee and Green Coffee Beans
– Tasting Chararcteristics of Good Coffee
Learn how we at Burman Coffee Traders evaluate coffee beans from the variety of coffee growers across the world? What are the characteristics we use to judge and how do we ensure there is a variety of selections to accommodate different individual taste and aroma preferences