Every year, the trade show at the SCAA annual conference includes at least a few vendors selling the latest and greatest technology to filter, purify, ionize or otherwise ensure the quality of the water you put in your coffee. We are reminded that water is the principal ingredient in the coffee, after all. But you rarely hear anything at SCAA about the countless millions of gallons of water that are used to mill your coffee at origin. Increasingly, smallholder farmers are turning toward “semi-dry” wet mills like the one pictured here that dramatically reduce the amount of water needed for milling, leaving the balance for families to drink, cook, wash and farm with. As it turns out, the best water may be the water that doesn’t go into your coffee.
In standard wet milling processes, copious amounts of water are used to propel freshly picked coffee cherries into depulpers and through the channels that lead them to the tanks where they will ferment. After the beans are fermeted for just the right amount of time — a contested issue of no small consequence that merits another post on another day — more water is used to wash them. (Where that water goes and what it does to local water tables across the coffeelands is another issue of serious consequence worthy of its own post later, but the focus here is on the volume of water used in the wet milling process.)
I have seen several estimates of the amount of water used during this process from different countries, and the most common figure seems to be about 1200 liters of water for every 100 pounds of fresh cherries. Those 100 pounds of cherries will produce about 16 pounds of export-ready coffee. These 16 pounds of export-ready coffee will lose about 20 percent of their volume in the roasting process, meaning that those 1200 liters of water will have been necessary to get just over 12 pounds of roasted coffee to market. That comes out to almost 100 liters for the last pound of fresh-roasted coffee you bought.
Increasingly, farmers — like those at Santa Anita de la Unión in Guatemala — are using a “semi-dry” wet milling process in which the cherries are propelled manually into a floating tank with a fixed amount of water that separates the quakers from the good beans before being passed to the depulper. This measure alone reduces considerably the amount of water needed for wet milling. But it is often combined with another measure — recycling the water from the depulping process for washing the beans after fermentation — that reduces water use even further. (As I have been led to understand, the water actually picks up bacteria in the depulping process that improve the quality of the washing process…Still looking for the research behind that and will update this post after I get a chance to review it.)
The most common estimate I have heard of the amount of water used in this process is 200 liters for every 100 pounds of cherries. That works out to less than 17 liters per pound of roasted coffee — a very favorable comparison indeed to the 100 liters used in traditional processes. What happens to the 1000 liters of water not used in “ecological” wet milling? It means more water for drinking. It means more water irrigation of coffee nurseries and other non-coffee crops that require it. It means more water for domestic uses, like cooking and cleaning. And it likely means significant conservation of limited water resources — no small achievement in the era of climate change.