When Stanford University graduate students Kristen Dobson and Calder Hughes studied how coffee moves from harvest to our coffee mugs, their research into the process of harvesting and preparing coffee beans revealed that small farmers lack data on a crucial step in the fermentation process that affects quality.
Coffee beans are derived from coffee cherries and must be removed from within the cherry on their journey to roasting. One method used to separate the green coffee bean from leftover layers of cherry skin, mucilage and sugar is fermentation.
Fermentation (referred to as the wet or washed method) is sometimes preferred over machine removal of leftover cherry mucilage because it is believed to enhance the body and flavor of the bean. It involves depositing coffee beans into large tanks and leaving the beans to ferment in the sugars left from the cherry. It can take anywhere from 12 hours to a few days for the process to complete. The moment during fermentation at which farmers remove the beans has a significant impact on flavor, making the regulation of fermentation crucial to delivering a delicious end product.
Dobson and Hughes discovered Columbian farmers had difficultly regulating the moment at which fermentation was complete. Farmers monitor fermentation using subjective measures such as sight and touch.
There is a window during fermentation where the bean reaches its optimal flavor. Removing the bean within this window ensures a tasty coffee brew. On either side of this window the bean will be fine, but further away from the window of optimization the bean must be thrown away.
“We decided to create a device to measure fermentation and help the farmer have quality control over his beans,” said Hughes. The answer was pH probes.
“Studies showed that monitoring the pH of the solution in the fermentation tank is an objective, more precise method to optimize results,” said Dobson. By taking measures of the pH of the fermentation solution, farmers receive accurate readings of how far along the beans are and when to remove the beans from the solution, thereby delivering a higher output of quality beans.
The device Dobson and Hughes created is called Compadre de Calidad and provides feedback to coffee farmers using LED lights and SMS messaging. At first, Dobson and Hughes created a device to sit in the tank and give readings. However, after initial testing, they discovered a smoother method that would more seamlessly incorporate the process into farmers’ routines.
They noticed farmers stirring their tanks with paddles and decided it would be easier for farmers to use the pH reader if it was attached to a paddle. “We also realized that allowing the beans to touch the pH sensor directly led to less accurate pH readings,” said Dobson. “To fix this, we designed a plastic strainer to work as a protective covering for the sensor, which allows the liquid generated from the beans to move through the strainer while keeping the beans out of direct contact with the probe.”
One challenge involved accomplishing real, practical testing with the prototypes. When Dobson and Hughes took the prototype to showcase at the Let’s Talk Coffee conference in El Salvador, the duo wanted to ensure it was as functional and production ready as possible.
“We wanted to make the parts look as close to real products as possible instead of the bundled together prototypes we’d been using,” said Hughes. “So we designed them in CAD and sent them to Solid Concepts for 3D Printing.” Hughes, previously an unmanned aerial vehicles engineer in Oregon, had worked closely with Solid Concepts on processes and materials to further develop and enhance UAVs. “We needed professional looking housings for these devices and I knew from experience that Selective Laser Sintering (SLS) was durable and would make our devices look good. I knew what Solid Concepts was capable of when it came to making hardware that attracts customers, the finishing they could produce, and I knew I wanted a higher grade than what we could do in the labs here at Stanford.”
3D printing provided the housings for the electronics and the strainers protecting the pH probes. The casings and strainer were manufactured with Selective Laser Sintering (SLS) with a bed of powdered nylon and a CO2 laser. The laser sinters, or melts, patterns in consecutive layers until a cohesive product is revealed. The box housing the electronics used glass filled nylon treated with a proprietary ColorTek Black post processing to give it a seamless black color. Glass-filled nylons are favored for their strength over conventional nylons. The pieces are comparable to the durability of injection-molded plastics.
Dobson and Hughes provided the pH device to several dozen farmers with testing at two separate small farms. For most producers, the ideal fermentation range is between pH 4.4 and 3.8, starting around pH 6 and proceeding from basic to acidic. However, the exact range and specific target vary from farm to farm depending on climate, plant variety and picking standards. Noted Hughes, “Roasters are looking for a variety of flavors for their roasteries; this means that the fermentation profile one roaster wants may not be the same as another. In the end, most farmers are entrepreneurial by nature and exceptionally good at producing coffee.”