Understanding the Coffee Bean Roast Cycle

Understanding the Coffee Bean Roast Cycle

Coffee beans start off life as a small red berry. Once the berries are ready for harvesting, they are processed to remove the outer skin, pulp and parchment, until the seed or bean remains. This bean is then dried and known as a green coffee bean. In this state, the green coffee bean can be stored for long periods of time in the correct environment, with little degeneration to the quality of the bean.

Roasting the coffee bean provides the unique flavor and aromas associated with coffee. Unroasted coffee beans are unpalatable and therefore roasting is a necessity as the bean changes characteristics during this process. Roasting forces moisture out of the bean forcing it to expand and dry.

In the process, some of the natural sugars caramelize, creating the complex flavor of coffee. The roasting process is complete when the green bean has transformed to a brown bean, lighter in weight by +-18% and increasing in diameter by between 50-100%.

Soon after the roasting process, the beans begin to “degas” and lose their flavor. This degeneration process can occur in as little as one or two weeks.


The Various Stages of Coffee Bean Roasting:

These stages have been identified by professional coffee roasters:

  1. Green: The beans will retain their virgin green essence, even as they start to heat.
  2. Yellow: The color will become yellowish, and the beans will emit a grassy odor.
  3. Steam: Steam will rise from the beans. This is the water inside the beans evaporating.
  4. First Crack (Cinnamon Roast): Here’s where the real roasting begins. Sugars inside the beans caramelize, and a cracking sound is heard, like the sound of popcorn popping.
  5. City Roast: Following the first crack, the beans have reached City Roast, the minimum level of roast acceptable for most people’s grinding and brewing tastes.
  6. City Plus Roast: With further caramelization of sugars and the migration of oils, the beans swell in size and reach City Plus Roast. This is a popular and common level of roast to use.
  7. Full City Roast: Beyond the limits of City Plus is the Full City, an even darker roast that takes the beans to the verge of a second cracking.
  8. Second Crack (Full City Plus Roast): The beans undergo a second, more violent cracking and enter Full City Plus. This roast will reveal even more layers of intensity to the flavor.
  9. Dark Roast (French Roast): The smoke will become pungent, the sugars will burn as much as they can without ruining the flavor, and the beans overall structure will break down. This is the utmost limit of roasting within the confines of good flavor.
  10. Burn: Past the Dark Roasting stage, the smoke will become acrid, and the beans will burn.

NB: Some roasting charts may include more or less roast distinctions than provided above.


Understanding the Different Roasts

Personal taste dictates the type of roast each individual may prefer. These may be classified into some common categories, however, there are numerous categories in-between.

For example, a Full City and a Full City Plus are both considered Dark Roasts, however, differences in the roasting process will determine which category the beans fall into.

The roasting process causes the internal temperature of the bean to rise, together with the temperature of the roaster and the internal temperature of the beans at the time they are removed from the heat.


Light Roast

To achieve a light roast, an internal temperature of between 356-401°F is required. These roasts are commonly called Light Roasts, Light City, Half City and Cinnamon Roast. Regardless of the name, these tend to form at the beginning of the first crack. At this point, the bean surface is still dry, and the beans may be rather dense or hard, particularly if the beans are removed prior to the first crack.

This roast is suitable for those preferring a higher acidity or “brighter” brew with a light body. This roast requires less time and a lower temperature.


Medium Roast
To achieve medium roasts, including City and City+, the temperature should range between 410-428°F. At this stage, the beans should still have a relatively dry surface and are more clearly distinguishable from the original green beans. This roast appears around the middle to end of the first crack. Some consider anything between first and second crack to be a medium roast as well.

This roast tends to be more popular than light roasts as the acidity is around the mid-level with a fuller body. This roast temperature is manageable for most home roasting.


Medium-Dark Roast
This category encompasses a broader roast band, in terms of how many roast distinctions are drawn including Full-City, Full-City+ and may encompass Vienna Roast. The temperature window at this stage is significantly smaller, between 437°F- 446°F. At this stage patches of oil are becoming visible as the beans approach a second crack.

This roast stage is recommended for Middle Eastern brews.

At this stage, the roast flavors begin to feature more prominently alongside the varietal notes, creating hints of spice and a heavier body.


Dark Roast
Finally, the dark roast encompasses the French, Italian and Espresso Roasts. This roast is achieved at temperatures around 464°F, however, most importantly, temperature should not exceed 482°F. To achieve this roast requires the correct equipment to be used due to the high temperatures and increased oils exuding from the beans. At this stage the acidity is low during the second crack.

At this stage, many consider the roast character may eclipse the origin character when it comes to flavor. Roasting beyond this stage will result in burnt beans and the potential for the beans to ignite. It is recommended to undertake this roasting in particular, in a well ventilated area, preferably outdoors or with good air extraction.


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