What is the purpose of the colorimeter in coffee?

Within the exciting world of coffee, we find a tool that plays a fundamental role when certifying the degree of roast of the beans or ground coffee: the colorimeter.

This device has become a valuable ally for the experts in the coffee industry. Its advanced technology allows for obtaining objective measurements that facilitate quality control in the coffee roasting stage.

What is a colorimeter?

The colorimeter allows an objective measurement of the color of roasted coffee and establishes reference standards to ensure consistency in production.

By using this tool, producers, roasters, and cuppers can guarantee the quality and uniformity of the final product. It also allows them to develop roasting profiles, that is, to make adjustments in the roasting process to achieve specific results in terms of flavor and aroma.

How does the colorimeter work?

The colorimeter emits light on the coffee and measures its reflected amount. They are compared with color scales such as the Agtron, assigning numerical values and facilitating the classification and comparison of coffee. For example, the Specialty Coffee Association recommends a certain roast level according to the Agtron scale:

Roast for cupping should meet the Agtron “gourmet” color score of 58 for coffee beans, 63 for ground coffee, ±1 unit, or between scores of 55 and 60 on the Agtron “standard” scale. If an Agtron machine is not available, whole bean roasted coffee should correspond to Agtron roast slip #55.

SCAA roast level for cupping

How is a numerical value assigned in the colorimeter?

In the process of assigning numerical values in a colorimeter, various systems, and color scales are used. One of the most commonly used systems is the Agtron scale, which provides a standard reference for coffee color classification.

The colorimeter emits white light into the coffee sample and measures the amount of light reflected or transmitted at different wavelengths. This information is used to obtain a numerical representation of the color of the sample.

The numerical values obtained are assigned to each sample and are used to classify and compare the color of the coffee. In the case of the Agtron scale, the values range from 0 (absolute black) to 100 (absolute white). A lower value indicates a darker color, while a higher value indicates a lighter color.

The Agtron scale

The Agtron scale is a widely used tool for analyzing the color of coffee beans and determining the degree of roast. It consists of eight discs with different shades that are used to identify the different degrees of roast of coffee.

Agtron Scale
Agtron Scale

It works by shining ultraviolet light on a sample of ground or whole beans and measuring the level of reflection. The resulting value represents the roast level; higher values indicate a lighter roast, and lower values indicate a darker roast.

It consists of two main scales: the M-Basic (or Commercial Scale) and the Gourmet Scale. The Commercial Scale ranges from 0 to 100 and was designed for commercial roasters, while the Gourmet Scale ranges from 0 to 133 and is aimed at specialty roasters who prefer higher roast grades.

Both scales share the same zero pure carbon benchmark.

The highest points on the spectrum are 100.0 for the Commercial Scale and 133.0 for the Gourmet Scale. The Agtron Gourmet scale further categorizes roast levels, including Light, Medium Light, Medium, Medium Dark, Dark, and Very Dark, based on specific lumen values.

Here is a table that relates the roast level, the value on the commercial Agtron scale, and the characteristics of the coffee:

Roast levelAgtronCharacteristics
Light> 70Light brown to cinnamon color. Light-bodied, sometimes delicately fresh in flavor. No oil on the surface.
Medium-Light61-70Moderately light brown color. Bright, sweet acidity with clear green coffee distinctions.
Medium51-60Medium brown color. Balanced acidity, fuller body, with green coffee distinctions still apparent.
Medium-Dark41-50Deep brownish/black color. Spots of oil to a shiny surface. Richly to sharply bittersweet, scorched-wood roast notes are prominent. Muted acidity.
Dark35-40Black surface covered brightly with oil. Bitter/bittersweet tones dominate. Body thins, and green coffee distinctions are fully muted.
Very Dark25-34Black surface covered brightly with oil. Bitter/bittersweet tones dominate. Body thins and green coffee distinctions are fully muted.
Extremely Dark< 25Black, shiny surface. Burned bitter tones dominate.

Although the Agtron scale is reliable for evaluating roast levels based on color, roasters also consider other factors such as temperature, smell, and sound during the roasting process. These additional elements contribute to an overall understanding of the roast profile of the coffee.

How should you use a colorimeter?

Here is a step-by-step guide:

  1. Preparation: Make sure that the colorimeter is correctly calibrated.
  2. Sample preparation: It can be a small amount of coffee beans or a powdered sample, depending on the design and specifications of the colorimeter.
  3. Set the measurement mode: You can select between reflected or transmitted light measurements according to the device’s specific indications.
  4. Place the sample: Some devices have a chamber or a specific holder where the sample is placed.
  5. Take the measurement: Start the measurement by pressing the corresponding button on the colorimeter. The light source will be emitted on the sample, and the device will record the amount of reflected or transmitted light.
  6. Data logging: The colorimeter will provide a numerical value or reading of the color of the coffee sample. Record this data for later analysis and comparison.

Note: Remember to follow the specific instructions of your colorimeter manufacturer, as the steps and characteristics may vary depending on the model.

What is the ideal level of roast in coffee?

For quality coffees and most types of extraction, the ideal roast in coffee is medium light. This roasting level allows for highlighting the particular characteristics and notes of the bean, which are influenced by its origin and variety. Here are some of the advantages:

  1. Highlights the notes of origin: A medium-light roast allows the specific notes of the coffee, such as fruity, floral, or herbal nuances, to be more evident in the cup.
  2. Provides energy: It guarantees a coffee with a higher concentration of caffeine, which is ideal for satisfying your energy needs.
  3. Balanced body: The coffee retains lightness and fluidity in the mouth while enhancing the distinctive notes and avoiding excessive bitterness.
  4. Delicious without additives: Thanks to the medium-light roast, the coffee beans are not over-roasted, which preserves all the flavors and allows you to enjoy it without adding sugar or other additives.
  5. Versatility in preparation methods: A medium-light roast level can be adapted to various preparation methods, such as filtration, French press, or espresso.

What happens if we roast the coffee more or less?

  • The lighter roast brings out the coffee’s more delicate and acidic flavors and aromas, with more pronounced fruity and floral notes. At this level, the coffee tends to have more acidity, with a light body, and does not contribute cream to the final result in the cup.
  • The darker roasts highlight the intense and smoky flavors, with bitter notes of cocoa and low acidity, which makes the coffee heavier and more oily.

Advantages of the colorimeter at the time of roasting coffee

Using a colorimeter during the coffee bean roasting process can provide certain advantages. Here are some of them:

  1. Roast control: They can set specific color parameters to consistently ensure the beans are roasted.
  2. Consistency and quality: Using a colorimeter, roasters can maintain a constant roast level in different batches of coffee. This contributes to consistency in terms of flavor, aroma, and appearance of the coffee beans, influencing the final product’s quality.
  3. Evaluation and comparison: Precise color measurements can be taken at different points during the process and analyze how the roasting profile affects the final result. This helps them to refine their technique and achieve the desired flavor profiles.
  4. Efficiency and savings: Using a colorimeter can save time and resources. Instead of relying solely on visual and subjective experience, roasters can use objective measurements to determine the optimal roasting point.
  5. Research and development: Colorimeters allow roasters to experiment with different roasting variables and profiles, perform comparative analysis and accurately track the results.
Written by Pablo Barrantes Nevado
I am Pablo Barrantes, a coffee lover. I decided to start this website to solve all the doubts that arise every day when preparing our favorite drink: coffee. I am an industrial engineer by profession, but I have worked in coffee shops for many years, where I have learned all the secrets about coffee machines and coffee. My passion for coffee has led me to investigate and study beyond the obvious, and thanks to this, I can offer solutions and give news about coffee and coffee makers. I hope you enjoy reading as much as I research, document and write here.

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