Cleaning the Green

by

By Dan Shryock

Dave Weber is about to purchase a new green bean sorter. He needs one to better serve his customers.

Weber, a 25-year industry veteran and vice president at The Annex warehouse in the San Francisco Bay Area, is witnessing a change in coffee roasters’ needs. More and more of his customers want their green beans delivered much cleaner than in the past and they turn to The Annex to do it.

“I don’t feel the coffee is coming in that bad. A lot of the countries of origin are producing really clean products,” Weber said. “When we’re sampling coffee, we’re noticing a large percentage of the coffee is in good shape.”

But on occasion a few bags show more impurities than roasters want to accept. “I’m getting a few sticks and a few floaters,” he said. “There’s a goal of perfection and some people get alarmed. We have been asked ‘can you clean and grade my coffee?’  I’d like to do more [for customers] so I’ll  make the investment.”

The same is true at the DupuyGroup, a major warehousing company with US locations in Louisiana, Texas, Florida, and South Carolina.

“We are striving to differentiate ourselves and offer a more diverse variety of services than solely warehousing,” said Janet Colley Morse, Dupuy Group vice president. “We would like to be thought of as a one-stop solution to any green coffee handling need.“

And, to meet that goal, Dupuy provides cleaning services whether the beans arrive in bulk, supersacks, or burlap bags.

“All of our equipment was carefully selected to ensure the highest efficiency while maintaining very precise settings in order to reduce yield loss for our customers,” added Eduardo Montero, Dupuy’s senior director of strategic business development.

The basic steps for removing impurities has not changed over the years but an array of advanced technology now guarantees cleaner coffee at the country of origin or on arrival.

The search for impurities

Green beans flow through a sequence of machines to find and remove anything that could harm the quality of the roasted bean or the roaster itself.  It starts at the input hopper when the beans are removed from bags and placed in the bin. As the beans fall in, a vacuum sucks away dust and loose particles.

Beans then flow into a vibration sieve where foreign matter drops through a series of screens, each with defined mesh (typically No. 5 through No. 100). Objects smaller than the mesh are discarded as the coffee continues through the process.

The next step is a metal separator, a powerful electro-magnet that attracts metal objects, followed by a destoner that sifts and removes remaining pebbles and heavier flawed beans.

Historically, this has been done by hand and it continues in some countries where the work provides jobs and the cost of sorting equipment is prohibitive. Technology plays a key role when bean volume is high, speed and accuracy are vital and labor is more expensive. “From a technology point of view, it’s not different,” said Dr. Stefan Schenker head of coffee business for the Bühler Group, an industry leader. “It’s a combination of mechanical cleaning and then the advanced concepts of optical sorting.”

Like Dave Weber, Schenker acknowledges that most imported green coffee is much cleaner now than in years past. The goal remains, however, to achieve the cleanest supply possible.

“It’s amazing what you can still find in coffee,” Schenker said. “You can find all sorts of impurities. Bullets from pistols, plastic, wood, and coffee bean defects - black beans, brown beans, stinker beans, bleached beans, and insect damage. Those are the most common bean defects.”

Cleaning at the roastery

Mechanical equipment such as the vibration sieve, metal separator and destoner have been used for many years but advances in optical sorting continue to refine the quality of the beans headed into the roaster.

“Our beans usually are in pretty good shape when they arrive,” said Wes Herman, owner and c.e.o. of The Woods Coffee roaster in Lynden, Wash. “But (levels of impurities) vary depending on the people we work with in the country of origin.”

The Woods Coffee still takes extra steps once they open bags.

“We installed a vacuum system because green beans get very dirty and come with a lot of dust,” Herman said. “The bags are cut open and a ventilation system pulls all the dust and loose materials on the way into the bin.”

Herman also uses a destoner and “we specifically put in a magnet for loose metals so we avoid getting anything into our roasters.”

Throughout the process, high-speed conveyors eliminate excess chaff on the bean itself. “By the time we get the beans where they’re going to go, there’s no loose material on the green bean itself,” he said.

Cablevey Conveyors produces a closed system that helps remove chaff while moving whole beans.

“Our systems are enclosed, like a pneumatic, or vacuum, or aeromechanical system - but instead of using air to blow or suck the materials from point to point - we use an enclosed cable and disc combination to pull the fragile bean from one point to the next,” said Karl Seidel, Cablevey’s marketing manager. “The fines are removed as they come through our system naturally.”

Shining a light with sorters

Optical sorters then examine each bean and separate the good from the bad based on optical spectral response, color and shape. “Electronic sorting has been huge progress in the last 10 years,” the Bühler Group’s Schenker said. “In our Sortex unit, for example, every single bean runs down a chute and in a fraction of a second it is analyzed.”

Schenker explained that a light source illuminates each bean and sophisticated sensors identify flaws based on the spectral reflection in the visible light range and even in the light range not visible to the human eye.

“The sensor technology has made huge progress. Today we have much higher sensitivity and also there has been huge progress in how fast the software behind it analyzes the response from the sensor,” he said. “The sensors are faster and they can detect an entire spectrum of wave lengths and, based on that, they get better and better in finding the impurities.

“As soon as a piece has been detected and you want to separate it, there is an ejection device, a tiny nozzle that has to be very quick. Within a fraction of a second a valve opens and a little air stream blows out the defect and closes again.”

In Costa Rica, manufacturer Xeltron is preparing to unveil a new inline scan sorting machine at April’s Global Specialty Coffee Expo in Seattle. The new product, the XV model, uses inline scan cameras to generate high-definition images for analysis and sorting. “It’s a different sorting process altogether from our traditional models, although they all sort by color,” company president Andrea Castañeda said. “The XV has the latest CCD cameras and has a 30-channel tray for increased volume sorting.”

The new XV sorter compliments the company’s current XR and XC models. “The rejects of the XV can pass through the XR or XC so you can recuperate any beans you may want,” Castañeda said.

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The Xeltron 6-XC can process 6.1 metric tons per hour with up to 21 channels.

Xeltron, founded by Andrea’s father, Fernando Castañeda, in 1974, centers around an electronic eye he developed. “He created an electronic eye as a unique sorting process, a 360-degree way of looking at grains and beans,” Andrea said.

The XR sorter also can be used after roasting. “Our XR model can also sort roasted coffee, separating the lighter beans from the darker beans. This improves the taste and offers a more uniform appearance,” she said. “You can use one channel to sort green coffee and another to sort roasted coffee.”

Satake USA developed the Pikasen FMS2000, a full-color optical sorter for medium and small operations such as The Annex near San Francisco. The FMS2000 shines light on beans so a digital image can be captured and analyzed just as the beans are sorted. The machine, in both feeder and cascade intake designs, can handle as much as two tons per hour. The cascade design allows beans to flow via gravity into the machine. The feeder version holds product in a hopper until it moves into a vibrating feeder.

And, as reported in STiR’s October issue, Tomra Sorting Food has partnered with roaster manufacturer Probat to produce the LST free-fall laser sorter. Based on the Tomra Nimbus food sorter, the LST identifies and rejects impurities and flawed beans that are hard to detect.

Incoming products are analyzed and the best sorting parameters are automatically selected. That results in a lower false reject and the highest possible efficiency, Probat states. The high-resolution laser technology recognizes objects not detected by conventional sorters.

Delta Technology Corporation offers its TCS model - total color sorter - for both coffee processing both in the country of origin and at the warehouse after importation. The TCS is lauded for its accuracy in detecting and sorting subtle bean defects in a single pass through the machine.

Key features include an advanced multi-spectral LED lighting system, high-speed color cameras, and data processing using Windows-based control software. That software also provides internet connectivity between the customer and Delta for online calibration, diagnosis, and full operational support.

The TCS model revolutionizes how coffee is sorted, Delta states, because the machine not only spots common color defects but also locates and removes beans with more subtle flaws such as partial color defects, foreign material, and pin holes on the tip of the beans.

Cimbria’s SEA Chromex optical sorter features a new exagon interface that supports widgets to assist less experienced operators. A single database makes it possible to run the same sorting recipe on multiple units and record real-time statistics.

Future technologies

Advances, of course, continue to take shape. Schenker said that soon sorters will be able to identify beans based on chemical composition.

“That’s something that is in our pipeline,” he said of the Bühler Group. “These sensors get better and better. In the future, we will be able to sort a bean with a high or low sucrose content, for example. Once this is possible it will open a whole new field of opportunities. We will not only sort out the defects but also create different fractions of beans with different roasting behaviors.

“We really think this will revolutionize the market,” said Schenker, who holds a Ph.D. in coffee roasting processes. “Coffee roasters use different roasting profiles. If I can preselect by beans, this is a really big opportunity to get the most out of beans,” he said.