Basic Coffee Processing Information

Coffee Processing Methods-

A general guide to the various processing methods that Presta offers

Washed

The washed process is when the coffee cherries have the skin, fruit mucilage, and parchment layer removed quickly after picking. The cherries are initially sent through a de-pulper to remove the skin and majority of the mucilage before being soaked (technically fermentation) in large tanks to loosen the mucilage that remains attached, the beans are then flushed with water to rinse them clean and going through the wet mill to remove the parchment layer. The drying can be done either in a variety of ways, large industrial dryers for faster drying in more humid less sunny places, or, more often, large concrete pads, or raised beds where the coffee needs to be turned by hand to ensure consistent drying. Finally they are sent through a dry mill to remove the final protective layer around the beans, the parchment layer. Once the parchment is removed the beans are ready for sorting and grading.

Honey:
White, Yellow, Red, or Black

Honey processing is when the coffee cherries have their skin removed along with varying amounts of the fruit matter (or mucilage). The fruit that remains on the coffee seed (bean) changes through enzymatic reactions and oxidation encouraging the bean to develop different flavor compounds depending on how long the fruit matter is left on the seed. We classify the different amounts of time based on the color changes to the mucilage, white, yellow, red, or black. White meaning the bean was exposed for the shortest amount of time before the mucilage is removed, and black meaning the bean was left until the mucilage had completely darkened, and often completely dried, before removal. The name Honey comes from the sticky quality that the fruit matter has before it dries. 

Natural

Natural processed coffee uses the least amount of water and energy to accomplish the same goal of removing the coffee seed (bean) from the coffee cherry. Once harvested the coffee cherries are spread out to dry without removing any of the coffee fruit. The cherries can be dried in a number of ways, sun or shade, concrete pads or raised beds, mounded or flat, 10 days or 28 days, and with each variation from each producer, a slightly different result. Once the cherry is dried it is sent through a dry mill (often a regional facility) that removes the skin, (dry) fruit matter, and parchment layer at the same time. Though it is common practice to combine the green coffee from multiple farms to create a lot big enough for green coffee buyers (like us) to be interested, Presta also sources single farm, natural process coffees.

Anaerobic

Anaerobic Process is the use of controlled fermentation to manipulate the sugars and acids present in coffee cherries changing the flavor profile of the bean. All coffee goes through some form of fermentation (in the cherry after picking) but using a yeast mother mix, lactobacillus cultures, or other fruits (co-fermenting), producers can create a wide variety of flavor compounds. This processing method is constantly evolving as farmers experiment with new techniques (original "fermentation" technique is the Natural Process) but usually the Anaerobic Processing starts with sealing the coffee cherry (still in its skin) inside large plastic barrels or Grain-Pro coffee bags full of liquid (or sometimes gasses), each container has a one way valve so it can purge the oxygen as the coffee cherries release their own gas (CO2). The coffee is left in the oxygen free environment for anywhere from a few hours up to a week. Once the fermentation is complete the cherries can be either de-pulped, washed, and dried (Washed Anaerobic), or it can be left to dry in the cherry before being sent through a dry mill (Natural Anaerobic).

Variations of Anaerobic Include:

• Anaerobic Washed is when, after the fermentation process, the mucilage and parchment are removed quickly.
• Anaerobic Natural is where, after the fermentation process, the entire coffee cherry is left to dry fully (Usually 11% - 14% moisture content) before being sent through a dry mill to remove the dried skin, dried fruit matter, and parchment layer.
• Lactic uses Lactobacillus cultures to allow a controlled change, converting sugars in the coffee cherry into lactic acid. This processing method simultaneously changes the perceived sweetness and acidity of the roasted coffee bean.
• Carbonic Maceration uses carbon dioxide instead of a liquid to displace the oxygen. The CO2 also encourages the coffee cherries to break down creating their own liquid to ferment in.
• Thermal Shock heats the cherries before quickly cooling them (not letting them “cook”) to encourage changes to the sugars.