By Jenny Neill
Roast degree, under development, and over development – listen to coffee roasters talk shop and sooner or later you will hear these terms. Used alone or with other descriptors, each acts as professional shorthand for flavor profile. Some prefer the more romantic terms associated with cupping to assess quality. Even those, however, often choose to bring a more scientific analysis to bear when a signature product is not coming out of the roaster with the expected aromas, or with too much or too little acidity on the tongue once brewed.
Refractometers, tools available since the 19th century, give clues to a liquid’s sugar or soluble content. Just as roasters talk of over development, baristas talk of over extraction and using a Brix meter, a type of refractometer, can help assess extraction levels. Its popularity as a tool with baristas has attracted the attention of some roasters too.
John Johnson, coffee specialist at Rising Star Coffee Roasters in Cleveland, Ohio, considers measurements from his VST LAB Coffee III Refractometer a valuable adjunct to cupping coffees regularly. The Rising Star team collects data on such variables as air and bean temperature, and rate of temperature rise during roast cycles through a Roaster Dynamics control system as a way to standardize development of flavor profiles for products. Adding in readings from the VST Refractometer “…helps us interpret that data,” said Johnson.
One example Johnson gives is that “the amount of energy we have to get into the bean isn’t the same every season.” The ambient air in the roasting plant is much cooler in January when outside it could be 0°F with no humidity. Compare that to a day in July when daytime temperatures exceed 80°F with relative humidity well above 60%.
Jason Webb, director of Sinar Technology, suggested one of the products his company sells might also be useful to a roaster like Johnson. The Sinar BeanPro 6070 measures both moisture and the density of the whole bean. Both variables can shift how a roaster chooses to handle the roasting process and tracking moisture levels before and after will have increasing importance as the international definitions of quality shift.
That a cup of coffee should give pleasure is a given and implementing a quality control program is essential for any roaster who wants to ensure repeated success with that. However, the legal definition of quality is changing too as new or revised food safety rules progress from proposal to implemented requirement.
Soon, the brown brew must also prove to be free of certain chemicals or other defects. This is where the advances beyond the 19th century era hand-held refractometer become more important to understand.
The importance of standards
The science of measuring and interpreting energy and light advanced quickly with the first international standards being agreed to in the early 20th century. These developments were crucial to the development of many fields: photography, graphic design, and food science among them.
Why are color standards so important to understand when shopping for quality control equipment for roasted coffee? They have become an essential part of the language of food science.
Ann Hildreth, director of business development at Photovolt Instruments, said, international standards are important because “Measurements which are made need traceability to standards. The major international standards centers are in United Kingdom, Germany, United States, and Japan. These centers also have cross references between them. By having instruments which are traceable to these standards the measurements are accurate and correct around the world.”
Furthermore, more than one even narrower such standard exists for interpreting the data produced when taking measurements with instruments designed for coffee.
The meaning of scores
Today, because of modern spectrophotometry (the science of measuring how much a substance absorbs light by measuring the intensity of a beam as it passes through a sample) some of the most precise instruments use a light source outside the visible spectrum to illuminate samples.
Some experts in spectrophotometry get annoyed when coffee consultants refer to one of the commonly used scales as referring to color. Carl Staub, managing partner of Agtron Inc., explained that near-infrared spectrophotometry (NIR) involves measuring selected wavelengths of energy reflected from the surface of a sample substance.This is not energy that can be seen by the eye, and therefor to describe it as a color measurement is incorrect.
Staub’s point is well-taken. Just because an instrument can report findings in an Agtron number does not mean that it is using NIR to take those measurements. Color meters shine light and measure the reflectance based on the specific instrument’s capabilities. Those measurements then go through a software-automated, post-measurement interpretation to be able to provide a score meant to be equivalent to an Agtron score.
The latest light-measuring tools
The coffee industry would be nothing if not full of ongoing debate. There is much in general food science research that would seem to validate the assertion that NIR is a better tool for analyzing roast degree and therefore predicting flavor than instruments that use visible light.
Not everyone agrees. In a white paper, “Color Measurement of Roasted Coffee using HunterLab Spectrophotometer” published in 2014 by a team at Hunter Associates Lab, Inc., the authors noted “IR spectroscopy has the potential to provide information on weight loss and moisture content, chemical composition, and other related properties of coffee. However, the combination of these broad range of capabilities are rarely found in a single NIR instrument suitable for industrial quality and process control...”
In other words, most such tools are far too expensive for many businesses and typically found in academic or research and development settings.
Paul Barnes, Americas sales manager for HunterLab, suggested small but growing coffee roasters consider adding the ColorFlex EZ Coffee to their quality control program. The device has a small footprint with a width of 5.1 inches, a height of 6.3 inches, and a depth of 14.2 inches weighing in under 10 pounds. The pulsed Xenon lamp sends one flash per measurement up through a disposable sample cup and takes reading in the visible light spectrum (400nm-700nm).
For large volume plants, Barnes recommended the D25NC with coffee scales. The D25NC is a larger and heavier tool with a width of 14 inches, a height of 14 inches, and a depth of 19 inches weighing in at about 30 pounds. With it, the light source is a full spectrum, solid state LED system with an expected life of about five years. Like the ColorFlex EZ Coffee, it takes measurements in the visual spectral range, however it uses bursts of 25 flashes in one measurement cycle to give one averaged reading.
Agtron’s latest instruments are the M-BASIC II and E20-CP/II. As the name suggests, the M-BASIC II is the less sophisticated. However, both models use NIR illumination. The M-Basic via a solid-state lamp expected to last about 9 years; the lamp in the E20-CP/II, also solid-state, is rated to last about two years longer. Both models feature good analyzer to analyzer agreement. This feature is one sought after by large companies with multiple roasting plants who need to meet similar flavor profiles in coffees roasted in more than one facility worldwide. What makes the E20-CP/II more sophisticated is that it uses fully automated digital calibration and enables the operator to use both the commercial and gourmet Agtron scale through a keypad interface.
Two other tools worth noting are the Colorette 3b from Probat and the 580-PC from Photovolt. Both are smaller in size than the ColorFlex EZ and both present measurements to the operator using the SCAA Roast Coffee Classification numbers.
Modern instruments like the 580-PC track a bean during its journey from first crack... all the way through brown, and very dark (nearly black) roasts, said Hildreth.
“With classification of roasts so easy, roasters find time to focus on a broader range of roast recipes,” she said.