The color of coffee during roasting, is primarily used to evaluate when to stop the roasting process. There are light roasts, medium roasts, and dark roasts, which will each have different taste characteristics, using the same coffee bean sample, at the same temperature, but by changing the amount of roasting time.

Increasing the temperature will allow the roasted beans to reach the same color in a lesser amount of time, but will change other physical properties in the beans, and result in a different end product. In particular, beans roasted at higher temperatures, at shorter time periods, will produce larger beans, with more, as well as larger pores, allowing for easier migration of oils and moisture, to the surface. (See Pore Structure of Coffee Beans Affected by Roasting Conditions, Journal of Food Science Vol 65 No 3,2000 by S. Schenker, S. Handschin,B. Frey, R. Perin, and F. Escher) 

The physical and chemical properties of the green coffee bean, as well as the time, temperature, and color values employed during roasting, are the variables that comprise a, "roast profile".

When you take in to consideration the variations in crop characterisitics, resulting from different weather, and soil conditions, as well as differing methods of processing and storage, it's pretty easy to see why instrumenation used to evaluate any of these factors, should be accurate, quick, and as less prone to human error as is possible. 

Recent breakthroughs in analytical laser technology have
made it possible to monitor roasted coffee bean color 
in real time, allowing for automatic roaster shut off, and 
eliminating the human error aspect. 

However, because the coffee industry color standards, are 
based on older technologies, that although effective in their
day, require batch sampling,  and grinding the sample to 
provide uniformity in color, prior to analysis, it is still 
neccessary to perform these tasks, if one hopes to 
communicate their results to others. 

For this reason, ColorTrack was also developed as an advanced analytical benchtop instrument, with the capability to correlate, or calibrate to other types of technology already in use. 

er like the PhotoVolt 577A pictured in Fig 1, light is reflected off of the objects surface, and then passed through red, green, and blue glass filters (Tristimulus) , the amount of light passing through each filter then being measured and compared to a human eye simulation color model. 
Tristimulus Colorimeter
Some of the earliest color studies in coffee were done with a colorimeter, and the first standards were actually developed with this method. The hand held sensor is attached to the control unit by a cable, and calibrated to a black swatch initially (no color) ,and then to a color standard, then placed over the ground coffee to obtain a reading.  

For evaluation of roasted coffee, they require about the same amount of sample preparation, and give results as meaningful and accurate as a spectrophotometer, in about the same amount of time, the difference being the way in which the results are gathered. 
The spectrophotometer, like this Agtron Unit, provides illumination, in this case in the NIR Range of the color spectrum, and then passes the reflectance to a grating, which then breaks the reflectance in to the spectrum.It measures the amount of light at each wavelength, which is then fit to a color model.

Agtron further increased it's presence in the coffee sector by developing an inexpensive eye evaluated color chart for start up roasters.   

The numerical designations associated with the different shades of brown, are still used by many in the coffee industry, as a means to communicate the color of their roasts to buyers, and suppliers alike.

For this reason the ColorTrack System was developed with both it's native color scale, and the ability to calibrate to other color scales.
The ColorTrack Analyzer Fig. 3  isn't classified as a spectrophotometer or colorimeter. Instead, it is a true reflectometer. Although a spectrophotometer is also a reflectometer, the distinction, aside from the technology of the sensing apparatus and software, is that ColorTrack Technology does not operate in conjunction with a human simulation color model. 

It perhaps more simply, provides detailed statistical data on lightness and darkness in a relative color scale.

Colortrack's ability to sense different shades of materials with unparalleled accuracy, in a statistically validated format, is due to the transmitter and receivers ability to operate specifically in the 785 nanometer range of the color spectrum.  
The ColorTrack Benchtop, uses laser (light amplification by stimulated emission of radiation) as the light source, and fires at a rate of 10,000 indiviual readings per second. By allowing the sample to move beneath the laser via a turntable, a much larger sample area can be analyzed, thereby increasing accuracy.

Of course, it takes some pretty sophisticated software, and the help of a pc, to tabulate all of the data. (200,000 readings in a 20 second scan) And to make it easier to interpret that data, the results of the scan are represented graphicaly
along with the statistical average, mode, minimum and maximum values, and standard deviation. 

Lower equipment costs, less time and preparation, and enhanced accuracy, earned the ColorTrack Analyzer the 2009 SCAA Best New Product Open Class Award.  
Latest software version allows for on site correlation calibrations
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