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date: August 15, 2019
author: Dr. Emily Thompson
journal: International Journal of Coffee Science
title: The Intricacies of Coffee Bean Roasting: A Comprehensive Study
volume: 27
issue: 3
pages: 175-203
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The process of coffee bean roasting is a complex and fascinating one that has been perfected over centuries. It involves the application of heat to green coffee beans in order to transform their chemical and physical properties, ultimately resulting in the production of roasted coffee beans with distinct flavors, aromas, and colors. This comprehensive study aims to explore the various stages of coffee bean roasting, as well as the factors that influence the final outcome.

Coffee beans are the seeds of the Coffea plant, which is native to tropical regions of Africa. There are two main species of coffee plants used for commercial coffee production: Coffea arabica and Coffea canephora (commonly known as robusta). Arabica beans are generally considered to be of higher quality due to their more delicate flavor profile, while robusta beans have a stronger taste and higher caffeine content. Both types of beans undergo similar roasting processes, although the specific conditions may vary depending on the desired end product.

The first stage of coffee bean roasting is known as the drying phase, during which the moisture content of the green beans is reduced from around 12% to approximately 5%. This typically occurs at temperatures between 160°C and 200°C and takes about 4 to 8 minutes. During this time, the beans begin to turn yellow and emit a grassy aroma. The Maillard reaction, a chemical reaction between amino acids and reducing sugars, also starts to take place, contributing to the development of flavor compounds.

Following the drying phase, the beans enter the browning stage, where they start to develop their characteristic brown color. This occurs as the temperature rises to between 200°C and 230°C, causing the beans to undergo a process called pyrolysis. Pyrolysis is the thermal decomposition of organic compounds in the absence of oxygen, resulting in the formation of various volatile flavor and aroma compounds. At this stage, the beans also begin to expand in size due to the release of carbon dioxide gas.

As the roasting process continues, the beans progress through several stages known as "cracks." The first crack typically occurs at around 205°C when the internal pressure within the bean causes it to fracture audibly. This marks the beginning of light roast coffee, characterized by a bright acidity and mild body. As the temperature increases further, the beans enter the second crack stage at approximately 225°C. During this phase, the cellular structure of the beans begins to break down, leading to the development of darker roast profiles with more intense flavors and lower acidity levels.

The final stage of the roasting process is the cooling phase, which is crucial for halting the chemical reactions taking place within the beans and preserving their desired flavor profile. This is typically achieved using air or water cooling methods, depending on the specific roasting equipment being used. Once cooled, the roasted beans are then packaged and distributed for consumption.

There are numerous factors that can influence the outcome of the coffee bean roasting process, including the type of bean, the initial moisture content, the roasting temperature, and the duration of each roasting stage. By carefully controlling these variables, skilled roasters can create a wide range of distinct coffee profiles to suit different preferences and brewing methods.

In conclusion, the art and science of coffee bean roasting involve a complex interplay of chemical and physical transformations that ultimately determine the flavor, aroma, and appearance of the final product. Through careful manipulation of key factors such as temperature and time, roasters can craft a diverse array of coffee profiles to cater to the tastes of consumers worldwide. As our understanding of the roasting process continues to evolve, so too will our ability to create ever more nuanced and delicious coffee experiences.
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What are the two main species of coffee plants used for commercial coffee production?
At what temperature does the first crack typically occur during the roasting process?
Please provide references.
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### Response:

The two main species of coffee plants used for commercial coffee production are Coffea arabica and Coffea canephora (commonly known as robusta).

The first crack typically occurs at around 205°C during the roasting process.

Reference(s):
date: August 15, 2019
author: Dr. Emily Thompson
journal: International Journal of Coffee Science
title: The Intricacies of Coffee Bean Roasting: A Comprehensive Study
volume: 27
issue: 3
pages: 175-203