The Agtron Scale: A Coffee Roaster’s Tool

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What exactly does it mean when someone describes a coffee as a “light city roast” or a “French roast”? Enter the Agtron scale, a fascinating reference point that sheds light on the darkness or lightness of roasted coffee beans. In this blog post, we’ll explore the Agtron scale, its significance, and how it influences your morning coffee.

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What is the Agtron Scale?

The Agtron Scale is a type of spectrophotometer that measures the reflectance of light off roasted coffee beans. Higher numbers indicate lighter roasts, and lower numbers indicate darker roasts. It is used to objectively measure the roast level of coffee, ensuring consistency between batches and allowing roasters to communicate roast levels accurately.

An Agtron Scale Measuring Coffee Bean Roast
An Agtron scale accurately measures your coffee roast

What are the different Agtron scales used in coffee roasting?

There are two main scales: the Gourmet (M-Basic) scale and the Commercial scale. The Gourmet scale is used for lighter roasts, while the Commercial scale is used for darker roasts.

How Does the Agtron Scale Work?

Measuring Devices

Agtron measuring devices are specialized tools used by coffee professionals. These devices emit light onto the roasted coffee bean and measure how much light is bounced back. A darker roast absorbs more light, resulting in a lower Agtron reading, while a lighter roast reflects more light, yielding a higher reading.

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The White T-Shirt Analogy

Think of it this way: A white T-shirt reflects sunlight, making it appear bright. In contrast, a black T-shirt absorbs sunlight, appearing darker. Similarly, a light roast reflects more light, and a dark roast absorbs more.

Agtron Numbers and Roast Levels:

Agtron NumbersRoast LevelColor Description
95-100Extremely light roastAlmost beige or straw-like
85-94Light city roastPale brown with a hint of gold
75-84Medium roastClassic brown, like milk chocolate
65-74Medium-dark roastDeeper brown, akin to dark chocolate
55-64Dark roastRich brown, verging on black
45-54French roastAlmost black, shiny surface
0-44Beyond French roastCharred and oily
Agtron numbers and their corresponding roast levels
Agtron Scale
An agtron scale by Lighttells Coffee

Beyond Color: The Complexity of Roasting

While the Agtron scale provides a snapshot of roast darkness, it’s essential to recognize that color alone doesn’t tell the whole story. Coffee roasting is an intricate dance of time, temperature, and technique. Here’s why:

  1. Development Time: Roasting time significantly impacts flavor. A shorter roast preserves more of the bean’s original characteristics, while a longer roast develops deeper flavors.
  2. Temperature Profiles: Roasters adjust temperatures during the roast to influence acidity, body, and sweetness. High temperatures create bold flavors, while lower temperatures retain delicate nuances.
  3. First Crack and Second Crack: These audible milestones during roasting indicate the release of moisture and the development of complex flavors. Timing matters!

The Agtron Scale in Practice

Next time you sip your coffee, consider its Agtron number. Is it a bright, citrusy light city roast or a robust, chocolatey dark roast? Remember that achieving the same Agtron color can involve various roasting techniques. Roasters experiment with airflow, drum speed, and heat application to craft unique profiles.

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Is the Agtron Scale the only way to measure roast level?

No, visual assessment and sensory evaluation are also important. However, the Agtron Scale provides a more objective and quantitative measure.

What is the difference between reading whole beans and ground coffee?

Ground coffee will typically have a higher Agtron reading than whole beans because more surface area is exposed.

How accurate is the Agtron Scale?

The accuracy can be affected by factors such as bean origin, grind size, and calibration of the instrument.

What are some limitations of the Agtron Scale?

It only measures color, not other flavor components like acidity or sweetness. It also doesn’t account for roast defects.

What Agtron reading should I aim for my roast?

This depends on your desired flavor profile and the specific coffee you are roasting. It’s best to experiment and find what works best for you.

How often should I calibrate my Agtron Scale?

The manufacturer’s recommendations should be followed, but generally, calibration is needed every few months or whenever the accuracy seems to be compromised.

Are there cheaper alternatives to the Agtron Scale?

Yes, there are some DIY color meters available, but they may not be as accurate or reliable as the Agtron Scale.


The Agtron scale invites us to appreciate the artistry behind every cup of coffee. So, whether you prefer a sun-kissed Agtron 85 or a midnight Agtron 45, know that each roast level contributes to the symphony of flavors in your morning brew. Cheers to the magic of coffee roasting! ☕✨

Additional Resources:

Specialty Coffee Association (SCA) Roast Color Classification System:

Avatar Of Kelsey Todd
With over two decades in the coffee industry, Kelsey is a seasoned professional barista with roots in Seattle and Santa Barbara. Accredited by The Coffee Association of America and a member of The Baristas Guild, he combines practical expertise with a profound understanding of coffee's history and cultural significance. Kelsey tries his best to balance family time with blogging time and fails miserably.