Measuring in the Dark

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One of the most common questions I get as a roaster at Seattle Coffee Works is: What is your darkest roast coffee? (Answer: it’s Seattle Strong)

Dark roast coffee has a long tradition in Seattle and elsewhere, and there are many stories about why people started roasting coffee beans long enough to char or even burn the outside of the bean. Doubtless, some dark roasting started accidentally when an inattentive or inexperienced roaster left the beans in the oven too long.

Seattle Strong is our darkest roast coffee

Dark roasting allows a roaster to deeply caramelize naturally-occuring sugars in the coffee beans, to highlight distinctive bitter flavor notes that couple well with milk.

When done well, the result is a distinctly bold, full-bodied, cup. While the ability to create a consistent flavor profile is a boon, there are some downsides to dark roasting as well. The caramelization of the sugars in the coffee entails the destruction of the very compounds that give coffees their unique tastes. The cost of consistency is a loss of complexity. Dark roasting is sometimes used to mask inconsistencies or defects in the coffee beans.

Like most third-wave coffee roasters, Seattle Coffee Works roasts the vast majority of our coffees light or medium. Even our dark roast is lighter than the dark roasts found at most large coffee chains. The reasons we tend toward lighter roasts are:

  1. Our direct-trade coffees are super-premium grade, which means they are free of defects and extremely consistent due to careful sorting and handling in the drying and milling processes before they reach our roastery. Roasting light to medium retains the distinctive flavors of these extremely high quality coffee beans.
  2. We prefer and select varieties of coffee that show off the natural fruit flavors of the coffee. These bright and sweet flavors are showcased through light roasting, but overshadowed by dark roasting which breaks down the sugars and acids that make them possible.

Regularly cleaning coffee roasting and brewing equipment is especially important with dark roast coffee.

The environmental impacts of dark roasting are not insignificant. Dark roasting uses more gas, produces more smoke, and leaves more carbon and oily residue on our roasting and filtration equipment, resulting in higher costs to mitigate impacts. The Puget Sound Clean Air Agency, our region’s pollution regulating agency, closely monitors our roast levels and quantities for this reason.

If you use dark roast coffee at home, set aside time to thoroughly clean your coffee equipment, especially grinders, at least once a week to remove residues that can damage equipment and adversely affect flavor.

How Dark is Dark?

To determine how dark to roast coffee, roasters rely on their all of their senses. They taste, smell and observe the beans, to find the ideal degree of caramelization without burning them. Much like a chef developing a new dish, once the roaster figures out the right combination of time, temperature and taste, it’s important to record the recipe and document the desired darkness level of the resulting coffee beans.

To quantify the darkness of roast, coffee professionals use roast analyzers. The most renowned roast analyzer manufacturer is Agtron, a Nevada-based company that produces

color readers for a variety of industries. Agtron’s 100-point scale of roast measurement, the Gourmet Scale, is the industry standard for communicating roast degree.

Setting up coffee samples of each batch for roast level analysis.


Where a coffee falls on this scale is its “Agtron number”. Lower numbers represent darker roasts and higher numbers indicate a lighter roast. Agtron numbers offer a clear indicator of the roast level of a coffee.

At Seattle Coffee Works, we use a roast analyzer on every single batch of coffee. Our single origin offerings, which we roast light in order to preserve their specific flavors, score between 70 and 75.

Our medium roast coffees, such as Emerald City and Molly’s Blend, typically range from 62 – 65 on Agtron’s Gourmet Scale.

The Agtron number of our new dark roast blend, Seattle Strong, is 50.

By comparison, a large coffee chain’s Pike Place Blend scores 40; its “light” Veranda blend scores 57. A large donut chain’s coffee scores 68.

The Agtron roast analyzer determines the precise roast level of roasted coffee beans.

How does a roast analyzer work?

Roast analyzers use near infrared spectrophotometers to analyze roast samples and determine the level of roast. They do this by reflecting a narrow band of light off of a sample of whole bean or ground coffee and then analyzing it to determine the roast degree.

While it may seem like the machine is analyzing the color of the beans, the infrared spectrum that the roast analyzer uses is actually outside of the visible spectrum. This is important, because

determining roast level using visible light and color can vary based on ambient light, background, and other factors. (Agtron also produces color tiles that can be used to visually approximate roast level, but this is much less accurate than the roast analyzer.)

Color tiles like these from the Specialty Coffee Association can be used to estimate roast level visually.

Rather than relying on visible color, the band used by roast analyzers correlates to the caramelization of sucrose, which is the primary sugar in coffee. Caramelization of sucrose directly correlates to the other chemical changes associated with the degree of roast. By measuring how caramelized the sucrose has become, you can confidently determine the degree to

which the entire coffee has been roasted.

This correlation determines the endpoints of the Agtron scale: 0 represents the point at which sucrose has completely turned into carbon. 100 is the point when the caramelization of sucrose has just begun. This is why dark roasts have a lower Agtron number and light roasts have a higher Agtron number.

So if you prefer very dark roast coffee, aim low on the Agtron scale.

Try our Seattle Strong here: https://www.seattlecoffeeworks.com/seattle-strong.aspx