Optical Sorters Keep Watch for Flawed Beans

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By Katrina Avila Munichiello

Optical sorting equipment has played a valuable role in the coffee industry for decades. These machines have the critical job of identifying a wide array of defective coffee beans and extracting them with a precision that reduces unnecessary losses of quality product. Producers are experiencing a moment when drought and coffee leaf rust have been impacting some of the most important coffee-producing regions while at the same time, beans are commanding some of the highest prices to date. The cleanest and best quality samples of beans will receive the highest financial reward. But how are the current optical sorting machines able to help coffee sellers achieve this goal?

Rooting out the problems

There are several types of defects commonly found in coffee beans. There are color defects in which a bean is the wrong hue because it has been impacted by mold, fungus, or poor development. Other coffee plants produce harvests that have been damaged by insects. Some beans simply do not mature or grow properly, leaving them too light or shriveled. With roasted beans, producers may find that they have under-roasted or over-roasted the product, ruining its quality. There can also be foreign objects mixed in with the beans, including sticks, metallic particles, and rocks.

Coffee leaf rust has become a sizeable problem. Rust is an infection that begins to emerge on the leaves of coffee trees as small yellow spots. Over time the spots become larger and orange lesions develop on the bottom of the leaves. The fungus causes the leaves to drop too soon, and because the urediniospores that have developed can survive six weeks, new leaves are likely to also become infected. The disease can be further spread by wind and rain. Coffee leaf rust has caused great harm to coffee trees, making them susceptible to damage by insects called coffee berry borers or Broca.

Whether arising from biology or from poor handling of the product during harvest or processing, any of these defects can ruin the quality of a cup of coffee. “Any kind of stress on the trees will increase the number and types of defects found in the green coffee,” says Johanna Bot, sales director at Satake USA.

“Both the increasing demand for specialty coffees, as well as the challenges of climate change, mean that high quality optical sorters will continue to be of great value to coffee exporters.”

Optical sorting designers offer solutions 

Producers are faced with the challenge of eliminating these defects from their coffee supply without also removing good beans in the process. They need equipment that can find the errant beans and carefully extract it from the supply.

Bühler Group, headquartered in Switzerland, has been in the optical sorting business for more than sixty years, developing solutions both for producers of foodstuffs like grain, nuts, spices and rice as well as non-food products like plastics. The company’s SORTEX line provides this precision sorting for green or roasted robusta and arabica beans. SORTEX equipment combines the uses of high resolution cameras, InGaAs (indium gallium arsenide) and PROfile technology, high pressure ejectors and feed mechanisms. InGaAs makes use of the fact that vegetation can absorb energy while other materials reflect it. These photodectors are therefore able to clearly highlight foreign materials that may be mixed in with the bean supply. PROfile technology analyzes the shape and color of the beans. SORTEX B meets the needs of mainstream commodity coffee with up to five chutes for high capacity sorting while SORTEX A is aimed at those with more challenging sorting requirements, and includes more advanced lighting and inspection technologies.

“(Our equipment) optimizes capacity, sorting efficiency, and yield at a competitive price,” says Charith Gunawardena, Bühler’s head of optical sorting. “You need to get the right balance between these three factors to optimize the sorting performance required by the customer,” said Gunawardena.

With a heavy emphasis on the strong customer service base they have established globally, Bühler prides itself on being able to serve the entire value chain including green coffee growers, exporters, traders, the importers, and the roasters.

XELTRON of Costa Rica aims to increase the producers’ coffee volumes by “saving every good grain,” says company president Andrea Castañeda. A leader in the industry for more than 40 years, XELTRON provides their customers with two critical solutions: a teflon coated chute system that maximizes sorting volume and a roller system that creates a cushion of air allowing each bean to be analyzed individually. The equipment can recognize a wide range of colors and defects so settings can be customized for changing needs across seasons. XELTRON has recently upgraded their electronics, making the systems more robust, allowing for a smaller footprint and a more efficient process. “You guarantee your brand’s prestige by maintaining a uniform appearance and a consistent quality,” says Castañeda, “helping you increase your yield and accelerate the return on your investment.”

Since 1978, Texas-based Delta Technology Corporation has established itself as a respected manufacturer of sorting solutions, designing the equipment from the bottom up and producing their own metal works and components in-house. The i-IQ/TCS Trichromatic is a high production sorter that uses full color spectrum high-resolution RGB cameras and advanced color mapping to simplify adjustments, with options to suit small or large sorting needs. The i-iQ/CCD Monochromatic sorter is suited for robusta which are more recognizable by color, as well as arabica beans. This sorter’s cameras create 8,000 scans per second, maximizing accuracy of detection and incorporates pneumatic ejectors produced with longevity and precision in mind. The company believes that the experience of their team of technicians helps them stay tuned in to current (and future) customer needs. “The added value…that Delta as a quality optical sorter factory can give, is the efficiency and stability of the sorting, improving the quality of exportable products without sacrificing good product on the rejected one,” said Alvarado Pineda, Representaciones del Istmo, Guatemala, a distributor of Delta in Mexico and Central America.

Cimbria has established itself as a vital resource for custom-built processing, handling and sorting solutions. Founded in Denmark in 1947, Cimbria has become a worldwide presence in the sector. The company has developed a wide array of sorting equipment that is applicable to the needs of coffee. For example, Cimbria Dry Stoners use air flow and vibration to remove small stones, sticks, and metallic particles from the beans. As for optical sorters, their SEA line is used across food lines and even for glass and in the recycling and mining industries. The SEA Next provides up to seven chutes and allows for resorting and as many as 28 cameras for monochromatic, bichromatic, InGaAs and Near-InfraRed (NIR) spectroscopy technology. The SEA Chrome trichromatic, also with up to seven chutes, can provide 0.1 mm resolution on differences in shades of color. It also allows users to establish what defect sizes the machine will eject and which it will ignore.

Satake USA, Inc., a subsidiary of Satake Corporation of Japan, also designs and manufactures optical sorters for agricultural products like cereals, grains, and rice, as well as plastic pellets. The company installed its first color sorting machine for green coffee in 1952 in South Africa and has been refining and advancing its systems ever since. “The biggest benefit (of high quality optical sorting equipment) is the higher percentage yield of exported coffee. A 2 or 3% yield increase quickly pays for the machine,” says Johanna Bot, sales director of Satake’s Latin America Vision Systems. She notes that while primary defects are the easiest to detect, the identification and removal of sour beans is far more difficult to do without significant losses. Satake’s use of full color sorting and high speed air ejectors has advanced their progress toward a more efficient and economical sorting system.

“The challenge will continue to be to replicate the human eye’s ability to distinguish subtle color, shape, and texture differences, while reducing even further the amount of good beans rejected in this process,” said Bot.

Sorting the future

Large objects like stones and sticks in the coffee supply can ruin machinery. Sour beans, light beans, and over-roasted beans can ruin the brewed cup. The defects that must be detected may change depending on where the coffee was grown, the requirements of particular buyers and coffee type. Technologies that help producers isolate these problem beans and remove them carefully and precisely can result in coffee that is more appealing to consumers and, in the end, more financially valuable to producers.

Common Green Coffee Defects

The Specialty Coffee Association of America (SCAA) Green Arabica Coffee Classification System (GACCS) Protocols:  

• The SCAA GACCS determines the conversion or equivalent of single defects to full defects.

• The numbers of full defects are calculated on a basis of 350 grams of green coffee sample.

• Bean imperfections need to have the specific bean characteristics and criteria as they appear on the picture and physical description in the Defect Handbook to be considered a defect.

• A full defect can be a Category 1 (primary) or a Category 2 (secondary) defect.

• Specialty Grade samples must have zero Category 1 defects

and no more than five Category 2 defects.

• A full defect is composed of one or more single defects depending on the impact each one has on the cup.

• In the case that more than one defect is observed in a coffee bean, it shall be counted only as the defect that has the greatest impact on the quality of the cup, (the defects listed first in the SCAA Green Arabica Defect Handbook are considered to have the greatest impact on cup quality).

• The SCAA GACCS only defines two grades of coffee, Specialty Grade and Premium Grade.

• Where several beans are considered a full defect (such as 5 broken beans = 1 full defect) the calculation must be shown.

To order English or Spanish editions of The SCAA Arabica Green Coffee Defect Handbook, visit www.scaa.org ($35 spiral bound on hard board)