Coffee beans start as the seeds of mature coffee cherries. After being processed and dried by coffee farmers, they become green coffee beans with a slight grassy and fruity aroma.
Roasting coffee beans transforms them from green to brown, unlocking a complex array of flavors. During roasting, 800 to 1,000 different aromatic compounds are produced, which contribute to the coffee's flavor profile.
Roasters can influence these compounds and, consequently, the taste of the coffee through their roasting techniques. Each roaster has their own unique style, shaped by their roasting methods.
The Roasting Process
Dehydration Phase
The initial phase of roasting is the dehydration phase, where the moisture content of green coffee beans, typically around 8-12%, is reduced. This phase usually lasts 4-8 minutes and is crucial for building up thermal energy in the beans, as the subsequent phase is exothermic.
Maillard Reaction Phase
Around 160°C, the Maillard reaction begins, producing a rich, toasty aroma reminiscent of bread or butter.
This reaction involves the interaction of reducing sugars and amino acids, generating melanoidins, hundreds of different aromas, and volatile organic compounds. The Maillard reaction starts during the yellowing phase and continues throughout this period, contributing to the coffee's complex flavor profile.
Flavor Development Phase
After the Maillard reaction, as temperatures rise, you'll hear the first break, signaling the beginning of the exothermic phase. During the dehydration and Maillard phases, the beans accumulate thermal energy. As temperatures increase, steam pressure and carbon dioxide build up inside the beans, causing the accumulated energy to be released, resulting in the first break.
The period from the first break to the end of roasting is known as the development time. Insufficient development time can lead to overly acidic coffee that lacks sweetness, while excessive development time can result in a dull, burnt flavor. Both the development time and temperature changes need to be carefully managed. Typically, the development time is 15-25% of the total roasting time.
Roast Degree
Roast degree is one of the most important indicators in coffee roasting. The Specialty Coffee Association (SCA) promotes the use of infrared caramelization analysis values, the Agtron 10-level coffee roast color chart, or Agtron coffee roast analyzers to determine the roast level.
Lightly roasted coffee has the highest acidity, while dark roasted coffee has the most intense flavor. Floral and fruity aromas are most pronounced in light roasts, while the classic coffee flavors, caramel notes, and bitterness are more evident in dark roasts.
Light roasts develop a high concentration of volatile aromatic compounds, such as floral and fruity notes, due to the significant production of formic and acetic acids. As roasting continues, high-temperature degradation reactions occur, reducing the coffee's astringency, deepening its color, and producing roast and coffee flavors.
Roasting Time
Although roast degree has the most significant impact on coffee flavor, total roasting time and each roasting phase are also interconnected. Quick roasting techniques yield more aromatic compounds, such as fruit, floral, and nutty notes. In quick roasting, the initial development phase produces a higher concentration of these aromatic compounds.
However, not all beans are suitable for quick roasting. For example, while acidity is typically bright and pronounced in light roasts, espresso enthusiasts often prefer lower acidity. Slowing down the roasting process allows organic acids more time to break down, resulting in a less acidic coffee.
In recent years, roasting techniques have become more flexible. For instance, our light roast coffee beans are quickly roasted to maximize aroma while maintaining a light body and balanced acidity with a sweet finish. On the other hand, espresso beans benefit from a longer development phase, which reduces acidity and enhances body and overall balance.
Learning to roast coffee is an endless journey filled with surprises and knowledge at every stage. Our focus is on highlighting the unique characteristics of each coffee. We hope you enjoyed this article and gained new inspiration for your coffee journey.
