Coffee Processing Methods
What is coffee processing? And why should you care about it? “Processing” is a term that refers to everything that happens to a coffee cherry and bean in between the moment it is picked from the tree and the moment that it is ready for roasting. You should care about it because it has an enormous impact on flavor in the cup, possibly even more of an impact than where the coffee was grown and what variety it is.
Processing Methods
It isn’t easy to get beans ready to be roasted when you are starting with a complete coffee cherry (remember, the coffee bean is the seed at the center of a fruit which we call a cherry). Here are the different methods of doing just that:
Washed or Wet Process. In this method, after the cherries are picked, the skin and fruit pulp/mucilage are mechanically removed with a de-pulper, then the beans and the sticky layer of pectin that is still left around them are soaked in water. There is some fermentation happening during this stage, although at a relatively low, controlled level. Turbulent water is used to remove the remainder of the pectin. The beans are then dried and the parchment can easily be removed by a dry mill, leaving us with just the bean inside a very thin layer called silverskin. Now the beans can be bagged, exported, and stored until they go into the roaster.
Natural or Dry Process. In this method, after the cherries are picked, the entire cherry with the bean inside it is left to dry in the sun. Much more fermentation happens with this method - imagine leaving an apple outside in the sun for a month. When the appropriate dryness level is reached, typically after a few weeks, then everything except the silverskin can all be removed mechanically. The bean is then left with just the silverskin around it, ready for bagging/export/storage/roasting.
Honey Process. In this method, after the cherries are picked, the skin and possibly some amount of the fruit pulp/mucilage is removed, and then it is left to dry in the sun. The level of fermentation is somewhere in between that of washed and natural processing. After the appropriate dryness level is reached, the remaining pulp/mucilage/pectin/parchment can be removed mechanically and the bean + silverskin are ready to be bagged/exported/stored/roasted. “White honey” means most of the mucilage has been removed. “Yellow honey” means some of it has been removed. “Red honey” means a small amount has been removed. “Black honey” means essentially none of it has been removed.
Pulp Natural Process. This is just honey processing with only the skin having been removed, essentially the same thing as black honey processing.
Anaerobic Process. In this method, after the cherries are picked, all (in a “washed anaerobic”)/some (in a “honey anaerobic”/none (in a “natural anaerobic”) of the skin and fruit pulp/mucilage can be removed, and then the beans, possibly with the skins and/or fruit pulp that may have been removed, are fermented inside sealed vessels without the presence of oxygen. Eventually, the beans are removed and dried and ready for bagging/export/storage/roasting.
Carbonic Maceration. This is just anaerobic processing with a slight twist - carbon dioxide is introduced to the fermentation vessel to completely purge all of the oxygen. In “standard” anaerobic processing, the vessel would just be sealed, so there would be a small amount of oxygen at the beginning of the fermentation process.
Lactic Fermentation. Lactic acid cultures are added to the fermentation process in order to develop different flavors than would develop from fermentation by the natural yeasts and microorganisms that exist in/on the cherries/mucilage/etc.
Why does it matter?
Fermentation! Remember, coffee is a fruit, and bacteria, yeasts and other microorganisms love to live in the fruit pulp as it is full of sugars, nutrients, and other chemical compounds. Fermentation is basically the process of these microorganisms eating the nutrients, which changes some of the chemical compounds into new chemical compounds, including alcohol. So yes, this is the same thing that happens when wine/beer/cheese/bread and dozens of other food & beverage products are fermented. The more fermentation takes place, the fruitier, sweeter, and heavier bodied the coffee tends to be. Naturals, black/red honeys, and anaerobics tend to be like this. The less fermentation takes place, the cleaner and more acid-driven the coffee tends to be. Washed coffees as well as white and sometimes yellow honeys tend to be like this.
Anaerobic fermentation produces different chemical compounds than aerobic fermentation does, which is why naturally processed coffees taste different than carbonic maceration coffees, for example. Anaerobic fermentation typically happens much slower too, which also alters the flavor profile.
Too much of a good thing?
Newer, more experimental processing methods like carbonic maceration, lactic fermentation, and anaerobic fermentation in general have the ability to transform coffees that would have a relatively bland flavor profile if processed using the washed process method into something far more interesting and exciting. However, too much fermentation can make coffees literally taste like alcohol (we often get a rum-like flavor from anaerobics) or vinegar. Finding an anaerobic, or even a natural, that has been carefully fermented to avoid these kinds of flavors can be quite a challenge.
