When talking about coffee cherries, the word processing refers to the act of removing all of the cherry’s outer layers from the inner pit or seed. There are three basic methods of processing used in coffee producing regions:

  • dry method
  • wet method
  • semi-dry method (usually determined by the availability of clean water)

The dry (unwashed) processing method is the oldest method of processing where the cherries are simply picked and spread out to dry in the sun prior to removing the pulp. They are spread out on a flat surface and left in the sun to dry for multiple days, reducing the cherry’s moisture content to 9 – 13%.
Prior to being spread out in the sun, the cherries are usually sorted and cleaned manually, using a large sieve. During the separation process, under-ripe, over-ripe and unwanted or damaged cherries are removed along with dirt, soil, twigs and leaves.
Once dry, the cherries move on to the stripping (or hulling) process to separate the skin and parchment from the pit of the cherry (the coffee bean).

The wet (washed) processing method uses a substantial amount of water to remove the pulp before the seeds are dried. The cherries are sorted by immersion in water, allowing underdeveloped and over-ripe fruit to float along with sticks and leaves (which are removed), while the green and ripe fruit sink.
In a pulping machine, internal water pressure is used to push the cherries against a barrel shaped screen which has holes only large enough for the pit of the coffee cherry to pass through. Green cherries are hard and hence cannot be pulped.  Instead, they pass to the end of the barrel system and are separated from the ripe cherries.  The pressure inside the barrel controls how many cherries will be pulped.  Too high of a pressure will cause all of the cherries including the green to be pulped. Therefore close monitoring of the pressure is required.

The remainder of the pulp is removed by fermentation which is a chemical reaction. They are put into cement tanks with water and are allowed to ferment for 16-36 hours.  On the way to the fermentation tanks, another density separation can occur. The highest quality coffees are the densest and should be separated and fermented in a different tank. Once fermentation is complete, the beans are thoroughly washed with clean water in tanks or in special washing machines; the beans are moved to drying patios and dried to 11-12% moisture content.

Roasting Process

Specialty coffee is generally roasted in what is considered small batches, up to 500 lbs. The roasting process initiates a series of chemical reactions within the bean, during which aromatics, acids, oils and other flavor components are created and/or changed to produce the attributes and characteristics (aroma, flavor, body, acidity and finish) found in the final product. Roast time averages about fifteen minutes, but will vary depending on the attributes the roaster wishes to draw out of the bean.

Over the course of about fifteen minutes, coffee beans will lose moisture, turn from green to yellow to tan/brown and emit popping or crackling noises. During this process, the bean will also double in size.
Learn more about the Barrie House Roasting Process.

The two most common roasting methods are drum roasting and air roasting. In both methods, the common goal is to keep the coffee moving to produce an even roast.

  • Drum Roasting machines are generally powered by oil or gas, and apply mechanics similar to that of a house-hold dryer where the green beans are top-loaded through a hopper into a drum.  The drum then turns on a horizontal axis, tumbling the beans while the heat is applied (either directly or indirectly).  Once the beans reach the desired roast profile or color, they are allowed to spill into a cooling bin where the cooling process is aided by a large, rotating, rake-like arm.  Often, this arm is equipped with quenching heads that release a fine mist to help speed up the cooling process.
  • Thermal Roasting–an air roaster (or fluid bed roaster) may be natural gas powered and uses fast moving streams of hot air to keep the coffee beans moving while roasting the similar to a hot-air popcorn popper.