Purpose: This article provides a white paper on measuring the color of roasted coffee beans. The color of coffee is important because it is predominantly used to assess the degree of roasting. The ColorFlex L2 Coffee is specially designed to measure the color of roasted coffee grounds, freeze-dried coffee, and instant powders.

• Use on ColorFlex L2 Coffee: The paper describes how HunterLab instruments correlate visual assessments and the traditional Agtron scale.
• HCCI (Hunter Lab Coffee Color Index): This index is a linear fit between the SCAA visual scale and %Reflectance at 640nm. It allows for slight adjustments to fit historical data, although the SCAA scale itself is not adjustable by the end user.
• Reflectance at 640nm: Chosen for its significant differentiation between coffee standards in the visible spectrum.

Features of ColorFlex EZ Coffee

• Designed to measure lot-to-lot differences, improving consistency and batch-to-batch production quality.
• Provides a quick and easy way to determine the degree of roasting quantitatively.

SCAA Visual Coffee Standards

• The SCAA has produced eight visual color standards for roast classification, ranging from Very Light to Very Dark.
• The HunterLab ColorFlex EZ Coffee meter reports both SCAA # and SCAA Roast Classification, as well as the HCCI.

SCAA Specialty Coffee Association of America, Long Beach, CA 90831 USA, +562-432-7222, www.scaa.org - then search in their Online Store for item # R400100D SCAA/Agtron Roast Color Kit.

SCAA item R4001 consists of a light-weight black vinyl kit (10in x 12in x 1-3/4in) containing eight color disks, numbered in increments of 10 ranging from Very Light (tile # 95) to Very Dark (tile #25).

The kit also includes 2 background sheets, two standard Petri dishes for sample presentation for visual evaluation, and an easy-to-read manual. These (8) industry standard disks were designed to provide a visual guide for the degree of roast as a purchasing specification for both roasters and their customers. Reporting in SCAA visual grades is inherently less precise than using Hunter L, a, b or CIE L*, a*, b* color values and correlated SCAA Coffee #. For best results using this visual coffee color evaluation system, you need to use balanced white light that minimizes the glare off the card and visually offset the texture difference between the roast ground coffee and the flat, uniform coffee standard. The SCAA # and Roast Classification system can perform well as a purchasing specification.

The Hunter Lab ColorFlex EZ Coffee meter comes with a built-in correlation to report both SCAA # and SCAA Roast Classification, as well as the HCCI Hunter Lab Coffee Color Index used for roast process control.

FAQ: What is HCCI (HunterLab Coffee Color Index)?

Answer:

HCCI or Hunter Lab Coffee Color Index measures the reflectance of ground coffee products at 640 nm, which is optimal for defining the degree of roast. HCCI works best for measuring during the roasting process, taking the coffee product to a consistent end point.

HCCI = [HCCI_slope * R%(640 nm)] + HCCI_offset

where default coefficients for HCCI_offset = 3.32 and HCCI_slope = 1.958

HCCI* comes with a user-adjustable bias and offset in each setup to allow display in agreement with existing instruments. HCCI values are typically displayed to 1 decimal place.

The Hunter Lab ColorFlex L2 Coffee meter comes with a built-in correlation to report HCCI Hunter Lab Coffee Color Index, SCAA # and SCAA Roast Classification, all used to quantify the degree of coffee roast.

FAQ: Can the HCCI Index be used for any application that has a product that goes from dark brown to light brown? Like a contrast meter?

Answer:

HCCI can theoretically be used for other products that transition from dark brown to light brown, but verification is needed.

Be cautioned, however, that this metric was optimized based on the reflectance at 640nm. This is the spectral point of greatest change for the intended application of quantifying coffee roast color. Your customer's dark-to-light brown process should be similar, but they should look at the reflectance curves for a range of their product color to verify 640nm represents a significant change point with their process.

As alternate metrics, L* lightness value, b*/a* ratio or % Strength may also work to color quantify their process while being more robust as a metric and in more general use for all colors.

Attached is Hunter Lab's white paper for Coffee Color Measurement.

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