Despite being one of the most popular beverages worldwide, many coffee consumers are unaware of its captivating and fascinating journey from its origin until it takes on the form we all know and enjoy.
This article outlines the key chemical and physical variations between green and roasted coffee. This way, you can appreciate how these factors influence the diversity of flavors and sensory profiles that make coffee a beverage of infinite gustatory possibilities.
Green coffee vs. roasted coffee
Green coffee, also known as raw coffee, is the natural state of the coffee bean obtained after harvesting. In this stage, green beans lack roasted coffee’s characteristic flavor and aroma, despite having a high concentration of chemical compounds.
The roasting process is a stage where green coffee is transformed into beans with different sensory profiles and roast levels, such as light, medium, or dark. During roasting, coffee beans undergo significant chemical and physical changes.
Roasting affects the amount of oil released on the surface of the beans. Darker roasted coffee tends to have more oil on its surface, giving it a characteristic shine. Additionally, these beans may have a stronger and more bitter taste due to the greater degradation of chlorogenic acids during the roasting process.
In addition to chemical changes, roasted coffee beans are lighter and more voluminous than raw beans due to the loss of water and gases during the roasting process. Unlike green coffee, roasting gives the beans a more brittle texture, making them easier to grind for beverage preparation.
Roasting is an essential stage that transforms green coffee into roasted beans with unique flavors and aromas, giving rise to the variety of coffee profiles we can enjoy daily.
Chemical and physical changes in green coffee during roasting
The roasting process of green coffee involves a series of notable chemical and physical transformations:
- Chromatic Metamorphosis: From its initial green color, coffee undergoes a chromatic transition, shifting through yellow and cinnamon and finally reaching a characteristic brown hue.
- Weight Loss: During roasting, coffee significantly reduces its weight, losing between 15% and 20% of its original mass.
- Density Reduction: The density of raw coffee is approximately halved during the roasting process.
- Desiccation: Green coffee loses a significant amount of its moisture content, decreasing from 12% to around 1%.
- Volumetric Expansion: Coffee beans double in volume as they undergo roasting.
- Evolving Flavor Profile: In the early stages of roasting, coffee gains sweetness and body, but as it progresses, there’s a transition towards more bitter notes and a gradual loss of acidity.
- Aroma Development: The roasting process promotes the development of over 800 volatile compounds, each contributing to the characteristic aromatic complexity of coffee.
- Gas Generation: Various gases, with carbon dioxide (CO2) being the most prominent, are produced during roasting, along with water vapor and other substances that will influence the sensory properties of coffee.
Through these chemical and physical modifications, raw coffee transforms into the roasted coffe that we know, acquiring its spectrum of flavors and aromas that make it so captivating for coffee lovers worldwide.
Purpose of coffee roasting
The primary purpose of roasting is to enhance coffee’s flavor and aroma profile, transforming green beans into roasted beans ready to be ground and brewed into a delicious beverage.
Additionally, roasting allows for a range of roast levels, from lighter to darker, each with sensory characteristics. Furthermore, roasting reduces moisture and increases the volume of the beans, making them more brittle and suitable for grinding.
Roasting is essential to achieve the diversity and complexity of flavors that make coffee a cherished beverage worldwide.
Coffee roasting levels
The choice of roast level is a matter of personal preference, and each level highlights different aspects of flavor and coffee aroma. Coffee roasters and enthusiasts can experiment with and enjoy the wide variety of profiles offered by these different roast levels:
- Light Roast: Beans are roasted only until the first “crack.” At this level, the beans retain their light color and preserve more of the original characteristics of raw coffee. The resulting coffee has pronounced acidity and a light body, highlighting more fruity and floral notes.
- Medium Roast: Beans are roasted until shortly after the first “crack” or the beginning of the second “crack.” At this point, the beans take on a more golden or brown color and start developing balanced flavors and a rounder body. Medium roast coffee has moderate acidity with more caramelized and sweet notes.
- Dark Roast: Beans are roasted until they reach a dark, almost black color. At this stage, beans have lost their acidity and developed more bitter, roasted flavors. Dark roast coffee has a robust body and is often used for milk-based drinks due to its ability to stand out in blends.
