Posted on March 18, 2016
Coffee roasting is an intricate art that uses heat to coax specific aromas and flavors out of raw coffee beans, transforming them into the beloved beverage many of us depend on to start the day. Home roasting aficionados, artisanal small-batch roasters, and mass roasters alike continuously seek to perfect their roasting processes by experimenting with process variables to satisfy the palettes of today’s sophisticated and gustatorily educated coffee drinkers. Once the roasting process is over, debate rages about how to get the most out of the finished beans: Do I need a burr grinder? Is drip coffee ever okay? Is pour over better than a Chemex? As demand for and knowledge about “good” coffee has spread, the discourse surrounding what makes coffee good has become louder, more multifaceted, and complex than ever before.
But before roasting temperature, grinder type, and brewing methods enter the picture, everyone agrees that good coffee starts with good coffee beans. Without high-quality green coffee beans, the best roasting, grinding, and brewing practices in the world will still yield a less than optimal result. As such, coffee roasters must take great care to select beans that meet their criteria using specific quality parameters. However, there is currently no universal standard for grading and classifying green coffee. Instead, “each producing country has developed its own classification and grade charts, which are often also used to set minimum standards for exports.”1 These grading and classification systems exist primarily to “produce homogenous commercial lots,” rather than truly indicating an excellent product. In response, the Specialty Coffee Association of America (SCAA) has created its own Green Coffee Grading Protocols to facilitate identifying and grading specialty coffee products.2
Despite the lack of uniformity of grading, color is regarded as a prime indicator of coffee quality within all classification systems and is of particular importance to those who wish to go beyond minimum export standards and toward a higher level of product. The spectrophotometric color evaluation of green coffee beans allows coffee roasters to select only the best beans, enhancing both quality and consistency.
The Meaning of Color
The color of green coffee beans can be affected by a number of factors during cultivation, picking, drying, and milling and gives important clues about the characteristics a particular bean will take on during roasting and brewing. Acceptable beans fall into one of the following color categories:
Grayish-blue and grayish-green coffee beans are considered to be the most desirable, gaining their distinctive hue from gradually drying in the sun after washing while air evenly circulates around the beans. This gradual drying process results in a coffee that roasts well and gives a “well-balanced acidity, full body, and a rich coffee flavor free from any aftertaste.” On the other hand, a more rapid drying process will create “a parchment that splits open in the final drying” and may “have characteristics of light acidity to somewhat lacking acidity, light body, and a flat flavor in the cup.”
Green coffee beans with brownish tones are considered of inferior quality, as the hue indicates they may have been have been scorched during drying or picked while under or over-ripe. As a result, the beans produce “a very light acidity, light body, and, normally, overly dominant flavors,” making them more suitable for very dark roasts which can disguise their gustatory imperfections. Beans that fall outside of this spectrum—including faded, amber, green, and foxy beans—are generally regarded as inappropriate for further processing, as their undesirable color may indicate serious quality defects such as severe over-ripeness, over-fermentation, disease, insect damage, water damage, or growth in mineral-starved soil.
Spectrophotometric Color Evaluation of Green Coffee Beans
With a lack of universal grading standards, specialty coffee roasters often perform their own quality assessments on green coffee beans to ensure that only the best beans are chosen for roasting. As the Chicago Coffee Roastery says:
To find the best beans, we evaluate […] bean color, uniformity of size and color, [and] occurrence of any defects. The greater the number of defects found in a random sample of a lot of coffee, the lower the grade that lot is assigned. Higher quality coffee is more carefully sorted to remove all of the defects. This additional sorting takes more time, and as we all know, time is money, which is why higher grade coffee costs more.
Manual inspection of green coffee bean color is indeed time-consuming and laborious. Spectrophotometers offer a rapid, simple, and non-destructive method of color assessment that removes the need for labor-intensive sorting as well as the imprecision inherent to visual inspection. Today’s sophisticated spectrophotometric instruments are able to quickly measure the color of green coffee beans with extraordinary accuracy to facilitate more precise sorting and enhance consistency. With integrated height measurement capabilities, these tools can account for texture variation to produce precise quantification of chromatic information and alert operators to colors that fall outside of your chosen tolerance level, allowing you to immediately quarantine defective beans. As such, you can be assured that only the beans that meet your personal criteria are chosen for further processing and achieve the highest level of batch-to-batch consistency, ultimately augmenting the coherency of your roasting practices and fortifying your reputation for quality.
Full article with photos available here: