What are the Essentials of Coffee Bean Roasting Various Roasting Methods for Coffee Beans

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Understanding Coffee Roasting

When purchasing roasted coffee beans, you'll notice the color and shape of the coffee. If the beans are full-bodied and have uniform color, this indicates properly roasted, high-quality coffee. Additionally, after some time post-roasting, oil will appear on the surface of the beans. However, don't forget that even fresh coffee beans will develop surface oil after dark roasting.

Coffee roasting refers to the process of heating green beans to promote a series of physical and chemical reactions inside and outside the coffee beans. During this process, multiple flavors such as acidity, bitterness, and sweetness are generated, forming body and color tone, transforming green beans into dark brown beans.

Factors Affecting Coffee Flavor

Generally, coffee varieties and processing methods are the main factors affecting coffee flavor, but the roasting method also has a significant impact. Coffee is also a food ingredient, similar to how we cook - the freshness and type of ingredients are certainly important, but ultimately it depends on our control of heat. Among roasting degrees, the biggest difference lies in the significant flavor variations between light roast and dark roast. Therefore, whenever you're looking for a specific flavor, the primary determining factor is the coffee's roast degree.

Light Roast

Light roast is further divided into:

Very Light Roast (LIGHT Roast): The lightest roasting degree among all roasting stages, also known as light roast. The coffee bean surface shows a light cinnamon color, with insufficient taste and aroma. This state is almost undrinkable and is generally used for testing rather than tasting.

Light Roast (CINNAMON Roast): Also known as cinnamon roast. A common roasting degree with a cinnamon-colored appearance. The grassy smell has been eliminated, aroma is acceptable, and acidity is strong. It's a roasting degree often used for American coffee.

Medium Roast

Medium Roast (MEDIUM Roast): Also known as micro-medium roast. This medium roast degree, similar to light roast, is American-style. Besides acidity, bitterness also appears, resulting in good mouthfeel. Aroma, acidity, and body are moderate, often used for blended coffee roasting.

Medium-Dark Roast (HIGH Roast): Also known as concentration roast. This medium-dark roast is slightly stronger than micro-medium roast, with a slight dark tea color appearing on the surface, and bitterness becoming stronger. The coffee flavor has acidity with bitterness, excellent aroma and flavor characteristics, most commonly favored by Japanese and Central European coffee lovers. (Blue Mountain Coffee)

Medium-Dark Roast (CITY Roast): Also known as city roast. The most standard roasting degree where bitterness and acidity achieve balance, often used for French coffee. (Brazil, Colombia)

Dark Roast

Dark Roast (FULL-CITY Roast): Also known as deep city roast. Slightly stronger than medium-dark roast, with considerably darker color. Bitterness is stronger than acidity, belonging to Central and South American roasting methods, extremely suitable for preparing various iced coffees.

Different coffee roast degrees bring different mouthfeels, and preferences for flavors vary from person to person. Some people prefer medium-roasted beans, leaning toward the rich taste of coffee but not wanting the flavor to become too dull. The flavor is rich yet slightly retains the natural light aroma of coffee itself, allowing one to taste the unique scents of beans from different origins. However, for those who want to increase caffeine intake for quick morning awakening, it's recommended to drink lighter-roasted beans, which provide slightly more caffeine intake. The simplest way to experience which beans suit you is to brew two pots of coffee at once - one light roast and one dark roast - giving yourself the most personal coffee tasting experience.

Coffee Roasting Methods

Coffee roasting methods can be roughly divided into three main categories: direct fire, hot air, and semi-hot air. Different roasting techniques bring different changes to coffee beans:

Direct Fire Roasting: The biggest feature of direct fire coffee roasters is that the drum has small holes, allowing the heat source to directly contact the coffee beans. However, this makes heat control more difficult. But if properly controlled, the aroma expression of the coffee beans will be excellent.

Hot Air Roasting: Mainly uses powerful high-temperature hot air flow to blow the coffee beans inside the coffee roaster, allowing the beans to be agitated. It provides the best heat conduction effect, saving time and being faster in roasting, resulting in cleaner and brighter coffee flavors.

Semi-Hot Air Roasting: Also called semi-direct fire roasting. There are no holes on the contact surface between the drum and flame, but the seemingly tight drum actually has small holes on the innermost side, guiding hot air flow into the roaster to assist the drum's metal in heat conduction, allowing coffee beans to roast evenly. Heat adjustment is more convenient than direct fire roasting, with flavor characteristics featuring rich aftertaste and sweetness.

Compounds Formed During Roasting

You may have heard people say that volatile and non-volatile compounds are produced during roasting. Generally speaking, volatile compounds are aromas, while non-volatile compounds are flavors. But what exactly are these substances?

Volatile compounds are organic chemical substances with high vapor pressure at room temperature, many of which are formed during degradation reactions or in the development stage of roasting. When volatile compounds dissipate, we smell the unique aroma of this coffee, including:

Aldehydes: Bring fruity and green aromas.

Furans: Contribute to caramel aromas.

Pyrazines: Have earthy aromas.

Sulfur-containing compounds: Including 2-furylmethanethiol. Some of these compounds are often described as having "roasted coffee" aroma, but certain substances are not pleasant when smelled independently. For example, methanethiol smells like rotten vegetables.

Guaiacol: Has smoky and spicy aromas.

Carbon dioxide is a volatile substance that doesn't affect aroma but does impact body.

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