Extracting the beans

Deterioration begins immediately after the cherry is off the tree as the sugars begin to convert into starches. This naturally occurring process leads to rotting. Therefore coffee should be processed within ten hours of picking it.

Irrespective of the harvesting method, green coffee beans and overripe coffee cherries inevitably end up mixed with the perfectly ripe cherries and must be separated during coffee processing. Over ripe coffee cherries, undeveloped coffee cherries, sticks and leaves float in water.

Ripe coffee beans and green coffee cherries are dense and sink. Therefore, the first step in coffee production consists of separating the “floaters” from the “sinkers.”
The ripe and green cherries can be sent to the patios to be dried using the natural process of preparing coffee or can be sent to the coffee pulping machines.

Pulping Coffee

The first stage of coffee pulping is used to remove the green coffee cherries from the ripe cherries.

In the coffee pulping machinery, the internal pressure is monitored to push the coffee against a screen with holes only large enough for a coffee bean (not cherry) to pass through.
Since the ripe cherries are soft, they break and the coffee seed is released through the screen.
The green cherries are hard and cannot be pulped. Instead of passing through the screen, the green coffee beans pass to the end of the barrel system and are separated from the ripe coffee beans. The pressure inside the barrel controls how many cherries will be pulped.

Coffee Fermentation (Wet process)

The coffee beans covered in the slippery mucilage can be sent to the patios to dry as pulped natural coffees or can be sent to coffee fermentation tanks.

On the way to the fermentation tanks, another density separation may occur as the highest quality coffees are the densest and should be separated and fermented in a different tank.

The coffee fermentation tanks are used to remove the mucilage before drying. The pulped coffee beans are put into cement tanks with water and are allowed to ferment for 16-36 hrs. Once fermented the beans are the washed using large quantities of water.

Wet-Process: Wet-processing coffee is a relatively new method of removing the four layers surrounding the coffee bean. This process results in a coffee that is cleaner, brighter, and fruitier. Most countries with coffee valued for its perceived acidity, will process their coffee using the wet-process.

Semi Washed: The pulped natural method consists of pulping a coffee, but emitting the fermentation stage to remove the silverskin. This results in a beverage that has characteristics of both a dry- and wet-processed coffee. It is often sweeter than wet-processed coffees, has some of the body of a dry-processed coffee, but also retains some of the acidity of a wet-processed coffee.

This type of processing can only occur in countries where the humidity is low and the coffee covered in the sweet mucilage can be dried rapidly without fermenting. Brazil has made this method famous and produces some of the best pulped natural coffees in the world. All twenty winners of the Gourmet Cup competition in Brazil in 2000 processed their coffees using the pulped natural method.

Dry-Process: The dry-process (also known as the natural method) produces coffee that is heavy in body, sweet, smooth, and complex.

The coffee cherries are spread out in the sun, either on large concrete or brick patios or on matting raised to waist height on trestles. As the cherries dry, they are raked or turned by hand to ensure even drying and prevent mildew. It may take up to 4 weeks before the cherries are dried to the optimum moisture content, depending on the weather conditions. On larger plantations, machine-drying is sometimes used to speed up the process after the coffee has been pre-dried in the sun for a few days.

The drying operation is the most important stage of the process, since it affects the final quality of the green coffee. A coffee that has been over dried will become brittle and produce too many broken beans during hulling (broken beans are considered defective beans). Coffee that has not been dried sufficiently will be too moist and prone to rapid deterioration caused by the attack of fungi and bacteria.

The dry-process is often used in countries where rainfall is scarce and long periods of sunshine are available to dry the coffee properly. Most coffees from Indonesia, Ethiopia, Brazil, and Yemen are dry-processed.

Coffee Drying

Before shipment, coffee is dried and a coffee moisture meter is used to measure coffee bean moisture. Coffee must be dried from approximately 60% moisture content to 11-12% moisture content.

Coffee is typically dried on large patios made of asphalt or cement and then transferred to mechanical dryers.

The coffee on the drying patios is shifted every 30-40 minutes and is shaped into long rows of no more than 5 cm in height. Next to each row is open ground, which is warmed and dried by the sun.

The coffee is then shifted onto the dry portion of the patio, and the section where it was previously is now allowed to dry in the sun. This helps accelerate the coffee drying process and prevents fermentation and mouldy beans from developing.

Drying coffee solely by patio takes 6-7 days for washed coffees. 8-9 days for pulped naturals (semi-washed) and 12-14 days for natural (dry-processed) coffees. This is why coffee beans are typically dried on a patio until they reach a moisture content of 15% and are then transferred to mechanical dryers. Once the coffee reaches 25% moisture content or less, it can be piled at night and covered with cotton cloths to allow the coffee to breath. If it rains, these piles can also be covered with plastic.

Coffee should not be covered with burlap sacks since this will impart a distinct burlap flavour and aroma to the coffee.

The best, but least utilized method of drying coffee is by using drying tables.
In this method the pulped and fermented coffee is spread thinly on raised beds, which allows the air to pass on all sides of the coffee.

The coffee is mixed by hand and the drying that takes place is more uniform and fermentation is less likely.

Most coffee from Africa is dried in this manner and select coffee farms around the world are following their lead.