293. Coffee and water resources at origin

2012 August 13
by Michael Sheridan

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.

  • Wastewater.

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?
5 Responses leave one →
  1. 2012 August 13

    Michael, thanks for these posts and your deep dive into some big questions about the impact of coffee production. I would strongly suggest that the relationship between processing and quality be explored, or in your words, outlined as a question underneath the heading of “What we still need to learn.”

    The basic assumption in specialty coffee is that the washed process (depulped, fermented, washed, dried) produces a superior cup. But there’s been very little experimentation to prove that this is so, in fact, some experiments conducted in Rwanda a few years ago showed that demucilaged processing produced an equivalent or nearly equivalent cup quality. The bottom line is that the specialty industry is not really sure why we insist on washed coffees. It may be a result of the physical attributes/convenience of the process, rather than the flavor it produces. And if that is the case, new technology (demucilaging machines) may present an alternative that requires essentially no water and produces comparable results in the cup.

    Then of course, there are other processes—natural, pulped natural, which require no water. Not all producers are situated advantageously for these processes, but in general, I would suggest a correspondence between lack of access to sufficient water and increased likelihood of preferable conditions for alternative processing (ie dry climate).

    Perhaps it’s time for us to ask a few questions we haven’t asked in a long time?

  2. 2013 July 13

    The Kenya experience with pollution control for wet processing coffee is worth remembering. Very few washing stations have adopted the demucilaging machines. Instead they have improved the traditional pulping equipment by developing a recirculation system which reduces water consumption to about 1.1litre of process water per Kg cherry processed. This amount is the sum total of all operations – pulping, pre-grading, fermenting, washing, soaking & machinery clean-up. Sedimentation lagoons attached to each washing station (a legal requirement) receive the reduced amount of polluted water. The system is low-tech and not expensive.


    Alan Finney
    Coffee Processing Consultant

Trackbacks & Pingbacks

  1. Everything You Need To Know About Coffee Flour, Backed By Intellectual Ventures
  2. 8. Preliminary Thoughts on Wet-mill Water Use at Origin | The Caffeinated Engineer
  3. Coffee Flour | Organic Coffee News

Leave a Reply

Note: You can use basic XHTML in your comments. Your email address will never be published.

Subscribe to this comment feed via RSS