The Lab

Post-Harvest Coffee Processing: Natural

Natural coffee processing is also referred to as dry processing. It is the oldest form of coffee production and was considered lower quality at the beginning of the specialty coffee movement. These coffees tend to have a heavier body and they may be more fruit-forward. Naturally processed coffees can be commonly found in Brazil and parts of Africa.

The process is relatively simple, but there is greater risk compared to washed coffee. The coffee is picked and laid out to dry on patios or raised beds. The drying may take 3-6 weeks and is highly dependent on weather. The cherries are high in sugar and moisture initially, and they must be turned consistently in order to avoid mold or bacterial growth that can cause defects.

Starting with fully ripe cherry is most important in this processing method. Under or over ripe cherries can produce off flavors or increase the likelihood of defects. Cherry sorters have been developed that use a rotating screen drum. As the drum rotates, smaller unripe cherry will fall through the bottom into a separate channel and bigger ripe cherry will be carried to the front of the drum and exit into a different channel. This equipment is effective in sorting, but may be a costly investment so the sorting is most commonly done by hand.

The period of drying is important. Longer drying periods are generally associated with more fermented flavors like wine or whisky. Too short of a drying period will result in muted flavors if not enough fermentation occurs. Controlling the drying can be done by adjusting the drying bed depth or adjusting how often the coffee is raked and rotated. Covering the coffee on cold nights or mounding it can help conserve some of the heat and increase the microbial activity.

Activity of the microbes is largely responsible for the flavors of natural processed coffee. They produce aromatic compounds like alcohols, ketones, aldehydes, but the most impactful are believed to be esters. Different types of bacteria will breakdown the cherry in different ways and produce different aromatic compounds. Migration of flavor compounds to the bean itself is difficult because of the hard parchment layer, and it is still unclear what compounds can migrate to the seed and how that would be possible. Studies have shown that sugar content does not increase when a coffee cherry is naturally processed, but there may be migration of compounds that lead to a greater perceived sweetness.

The natural processing style is a way that producers are experimenting with elevating the quality of their coffee. It can help by imparting exciting flavors to a coffee when executed properly. Royal NY sources naturally processed coffee from a variety of coffee growing countries For more information on what is currently availabile, contact your trader.

Patrick McKeown

Patrick began his coffee journey on Long Island at a small coffee bar and roasting at home. Since then he has been a barista, manager, and craft roaster in NYC.