How Does Roasting Affect Coffee Flavor?
There are many factors which affect the flavor and intensity of good coffee, roasting being the number one. The various temperatures and lengths of time which coffee is roasted results in its flavor profile.
Just as how diamonds came to be through changes brought about by intense heat, coffee also goes through a series of processes that brings out its aroma, color, and flavor—the attributes that it is known and loved for.
The image that comes into most of people’s heads whenever they think of raw coffee is usually this little brown bean. However, these brown-colored coffee beans that we think about are not the rawest form of coffee. This fact may be a little surprising to many but coffee naturally comes from a cherry, from which the seeds are extracted and then dried. The unprocessed and crude form of coffee therefore is a green supple bean with grassy aroma—very different from the brown hard coffee bean with nutty, fruity, or earthy aroma that we usually think of.
How then did the brown coffee bean come about?
Roasting transforms green coffee beans into its characteristic brown color. Apart from the color, roasting also changes other chemical and physical features such as its acidity, sweetness, caffeine level, fluid volume, and protein content—consequently acquiring new flavor and aroma distinctive from its green coffee bean origin.
The Roasting Process
Before coffee is brewed, or in some cases ground into powder, it undergoes a roasting process. This practice dates back from the 15th century and from then on it is considered a routine and prerequisite step before brewing. Coffee roasters apply specific techniques and timing during the roasting process in order to achieve a certain flavor profile.
There are five phases in coffee roasting: drying, caramelization, and development phase.
Drying Phase - Coffee-roasting begins through sorting and weighing of the raw beans. There are several post-harvest procedures and strategies done which may be unique to the coffee origin or the manufacturer. The beans are then subjected into the roaster, allowing the beans to initially absorb heat until a peak temperature of 175 °C (347 °F). In this phase, most of the moisture from the seed is lost in the form of steam. This phase of the roasting process is exhibited by a change of color from green to yellow. With it being the first phase, the drying stage is a critical phase that needs to be done meticulously with the right time and temperature aimed at achieving a perfect requisite needed for the caramelization and development phase.
Caramelization Phase - Caramelization phase encompasses the period whereby the beans have turned to a color yellow, up until when the first crack can be heard. This phase is named such for the reason that the sugar present in the coffee beans are caramelized due to exposure to high temperatures. This phase is also termed as the “browning” phase which is with regards to the color change brought by the Maillard reaction—a non-enzymatic chemical reaction between amino acids and reducing sugars that is responsible for the characteristic brown color change. It is during this phase where the roast expresses its sweetness quality. This phase is concluded when the acquired pressure buildup from the beans is released, emitting an audible popping sound. Light roasts are usually stopped immediately at first crack. In other roasts, the beans are left for a longer time, proceeding towards the development phase.
Development Phase - The final phase lasts from the moment the first crack is heard until the conclusion of the roasting cycle. It is in this stage where flavors are modulated according to chemical reactions that accompany the endothermic process of roasting. A lot of the coffee’s attributes are being obtained and improved in this phase. Although it can be deemed that this phase is the most essential since it is in this phase where the flavors of the coffee are developed, the development phase is highly dependent and is dictated by how the preceding two phases are carried out. Coffee’s acidity, strength, sweetness, and flavor is fine-tuned during this stage.
The degree of how the beans are roasted—the “roast profile”—indicates the roasting technique applied to achieve a certain flavor characteristic. It is from the process of roasting from which coffee beans of a single origin become different or distinguished from each other. A light roast coffee will exhibit an origin character, while a darker roast will have a dominant roast character. The roast profile dictates the recipe for the roast outcome. One of the most common factors in a coffee’s roast profile is the bean color. There are also other types of coffee roasting profiles such as moisture content, moisture loss, post-roast temperature, bean density, coffee origin, and etc. Coffee roasters have designated names for the roast degree the beans are subjected to, such as “French roast” and “city roast”, and other specialized names. The most commonly used categorization for coffee are the roast names according to the bean color after the roasting phase.
Light Roast - The beans are moderately light brown and dry. This type of roast is suited for milder coffee varieties. Having spent less time in the roaster, this coffee showcases a truer origin based taste. Light roasted coffee has a higher caffeine level than their darker counterparts—a complete myth buster! Some coffee drinkers would go on with their lives thinking black coffee had the caffeine load ideal for their long days and long nights. But boy, they thought wrong. Light city, half city, and cinnamon roasts fall under this category.
Medium Roast - This roast is medium light brown in color and contains preserved origin flavors. The internal bean temperature for this roast ranges from 210 °C (410 °F) to 219 °C (426 °F). This roast lies on the gray area of the roast profile where the coffee flavor becomes a delightful combination of origin and roast character. American roasts and city roasts are medium roast coffee.
Medium Dark Roast - The bean color is dark brown with rich caramel flavor with a tinge of a bittersweet aftertaste. These beans are usually stopped roasting at the beginning or the middle of the second crack. In medium dark roast, the origin character is masked by the roast period. The acidity of this roast is dampened and the bean surface has a faint shine brought about by the thin coat of oil that is released along with heat.
Dark Roast - This roast has a characteristic rich black to charred color with a thick oily surface. The more time spent by the beans in the roaster enables the coffee to acquire more aroma compounds and flavor. This roast has striking bitterness, diminished acidity, and a burnt or smoky tang. Dark roasts have a roasting peak of 240 °C (464 °F) - 245 °C (473 °F). French toast and Italian roast are categorized under dark roast.
Intense heat will either break or make something. For coffee, it’s the latter; intense heat carries out elegant changes in the coffee’s physical and chemical properties that create a new attribute for itself.