I am writing this month about a coffee-water paradox in the coffeelands that I think has at least three dimensions. The first one is this: coffee farming may represent the leading (licit) livelihood option for farmers in the highlands, but it is a drain on scarce water resources and a leading source of water contamination for everyone living downstream from them.
What we think.
Coffee milling constitutes a threat to water security in Central America in two ways. First, it can be a drain on “blue water” reserves in water-constrained communities. Second, the wastewater that is often released untreated into local waterways is a significant source of contamination of surface water on which millions of people in coffee-growing watersheds depend.
About the wet-milling process.
Most specialty coffees are washed Arabicas. The term “washed” here refers to a wet-milling process that can use enormous volumes of water and release harmful contaminants into the local water supply.
- Water use.
The traditional wet-milling process begins when the pulp is removed from freshly harvested coffee cherry. The cherry is poured into a funnel that leads to a depulper, where it caught between the depulper’s outer casement and a cylindrical grate, removing the outer skin, or pulp. This leaves the seeds, or coffee beans, covered in sticky, gelatinous mucilage. The mucilage is then removed from the bean through a fermentation process that can last anywhere from 12 to 36 hours or more depending on local conditions and practices.
Where does the water use come in? One traditional method of depulping involves running a continuous stream of water through the depulper as it is operating, sometimes for hours at a time. Then following fermentation, the coffee is washed to remove the mucilage, a process that can require enormous volumes of water.
Some wet-milling processes use up to 1200 liters of water or more for each hundred-weight bag of coffee cherry, which may produce as little as 16 pounds of export-ready green coffee. For a single container of coffee, this translates into more than a quarter-million liters of water.
The wastewater from the wet milling process is one of the leading contaminants of local water sources in coffee-growing communities. The mucilage is so loaded with sugars and pectin that the viscous wastewater is referred to in Spanish as “agua miel,” or “honey water.” The sugars and pectin in the water are fermenting into acetic acid when they are released into local waterways, where they can only be broken down by oxygen in the water. But the amount of oxygen needed to break down pollutants in the wastewater – referred to as biological oxygen demand, or BOD – is so high that it exceeds the natural ability of rivers and streams to purify the coffee wastewater effluents. The net result is an anaerobic effect that threatens marine life and fosters the production of bacteria harmful to human health.
Coffee wastewater also releases methane into the atmosphere as it evaporates, contributing to climate change.
What we know.
- Many coffee mills use outdated technology that is water-intensive: they are using more water than they need to.
- About 90 percent of surface water in Central America is contaminated.
- Most coffee wastewater in the region goes untreated.
- Coffee wastewater contributes to surface water contamination throughout coffee-growing watersheds in Central America.
What we still need to learn.
While the general relationship between the coffee process and water availability and quality may be understood, they haven’t necessarily been quantified at a systemic level. Mapping the relationships between the coffee process, water availability in coffee communities, and downstream water quality would be a major contribution to the state of knowledge around coffee and water at origin. Key research questions include:
- How much water does the wet-milling process use at the watershed level, and how does it affect water reserves?
- How does the use of water in the wet milling process related to the rate at which sustainable coffee agroforestry practices replenish the water supply?
- How much does coffee wastewater contribute to the contamination of surface water for downstream users?