What Determines the Roast Level of Coffee Beans? How Does Roast Degree Affect Coffee Flavor?

Coffee flavor derives from three main sources: 60% from green beans, 30% from roasting, and 10% from brewing. This demonstrates that multiple factors influence coffee flavor. So how does a roaster determine the roasting degree of coffee beans? Today, FrontStreet Coffee will discuss how to determine roasting styles.

It's important to note two key points: First, each roaster's understanding of coffee beans differs, leading to varying choices in roasting degree. There isn't necessarily absolute right or wrong—merely different choices in flavor expression. This isn't a universal standard. Second, roasting degree also lacks a strict standardized measurement.

Typically, roasting degree is named according to coffee bean color, based on a standard color wheel. The common names we see in textbooks—cinnamon, city, Vienna, French, and dark French—originate from this system. This standard represents only general international terminology, but in actual roasting practice, exceptions often occur and are not uncommon. For example, beans from some origins don't color easily, and further roasting would create bitter, scorched flavors, forcing the roaster to stop despite the light appearance because the desired flavor has already developed. In other origins, beans might appear darker due to higher caramel content after roasting. In these cases, color value serves merely as a reference standard.

Some people use the drop temperature (ending temperature) as the standard for roasting degree, but in reality, different brands or technical approaches to roasting machines show variations. Comparing drop temperatures between different roasters shows significant differences, which explains why we often see Japanese roasting curves ending at 230-240°C.

The Roasting Process

Roasting transforms the chemical and physical properties of green coffee beans into roasted coffee products. This process lasts ten to fifteen minutes at temperatures exceeding 200°C, undergoing multiple chemical changes, producing first and second cracks—popping sounds similar to popcorn—while losing moisture. This causes the beans to expand and change their color, texture, aroma, and density. During roasting, chlorogenic acid gradually disappears, releasing familiar and pleasant fruit acids like acetic acid, citric acid, and malic acid found in wine. Proper roasting appropriately presents these desirable acids in moderation, thus creating coffee's unique flavor profile.

Theoretically, any appropriate moment after the first crack could be chosen for dropping the beans. However, to avoid risks, roasters typically don't drop immediately after first crack begins but prefer to develop the beans for a few more degrees to achieve fuller aroma development. This means from approximately 2°C after first crack to slightly after second crack—a total range of merely 10°C—we can roughly simplify into three roasting styles: light, medium, and dark. From this, we can see that their drop temperatures don't differ significantly—sometimes by only 2-3°C—yet their appearance differs markedly. Therefore, we combine color, form, and flavor to describe a coffee bean's roasting degree.

Roasting Styles from Different Perspectives

From a roasting perspective:

As FrontStreet Coffee mentioned in their barista assessments, light roast refers to coffee beans dropped during the middle to end stages of first crack, characterized by enzymatic activity and early Maillard reactions. The organic acids in the beans haven't completely broken down yet, resulting in prominent acidity with minimal bitterness—perfect for friends who enjoy acidic coffee.

Medium roast typically refers to beans dropped between the end of first crack and before second crack. At this stage, caramelization occurs with more Maillard reactions. While acidic aromas remain, they're noticeably weaker than in light roasts. The balance between acidity and bitterness creates a more prominent sweet flavor, making it exceptionally smooth with caramel and chocolate as primary notes. This roasting degree often allows specialty coffee to express its optimal characteristics and is also the most commonly used roasting degree at FrontStreet Coffee.

Dark roast typically refers to beans dropped after second crack. The caramelization reaction approaches completion, dominated by Maillard reactions, producing resinous, spicy, and carbonized aromas.

How We Determine Different Roasting Degrees

So how do we decide on these different roasting degrees?

The first basis is history. Previously, consumers didn't have high expectations for coffee flavor, focusing more on its functional aspects. During this lengthy period, coffee roasting degrees were remarkably consistent—dark. Therefore, the styles formed by major coffee-producing regions over these hundreds of centuries primarily emphasized richness and body, such as Mandheling, Brazilian, Colombian, or Blue Mountain. In comparison, Blue Mountain offers richness without prominent scorching bitterness, perhaps making it an important factor in becoming the king of coffee in earlier eras. This roasting influence remains profound today—some consumers' habit of requesting sugar and milk when ordering coffee stems from this tradition.

Therefore, in roasting selections, we strive to return coffee beans from these classic origins to their historical era, maintaining classic rich flavor profiles.

Taking Mandheling as an example, its unique "heavy profile" creates a satisfying, unbridled feeling when consumed—enjoyed by many men, and now increasingly popular among women as well. Indonesia is the world's largest archipelagic country, known as the "country of a thousand islands." Indonesia's higher altitudes, volcanic ash soil, and climate characteristics provide excellent conditions for Arabica coffee tree growth. Sumatra has long been known as the "spice island," where coffee trees in mountainous areas grow alongside wildlife, cloves, cardamom, and pepper. Combined with the unique three-stage drying processing method (wet hulling), this creates Mandheling's distinctive flavor: unique herbal notes, woody incense aromas, moderate acidity, mellow yet bittersweet complexity like life itself, and strong aftertaste.

Mandheling coffee beans are relatively large with hard density. To highlight their famous richness, low acidity, and local herbal flavors, FrontStreet Coffee employs dark roasting. If Mandheling beans were light or medium roasted, the flavor might not achieve the richness that everyone loves, and acidity would become more prominent, no longer making it the Mandheling coffee everyone enjoys. Of course, if someone prefers acidic Mandheling, they could try medium roast—but then again, without Mandheling's characteristic flavor, can we still call it Mandheling?

The second basis is the bean's physical form and characteristics. For example, Yirgacheffe coffee beans are typically chosen for light roasting. This isn't because this origin inherently shows good acidity—quite the opposite. It's because extremely light roasting causes its acidity characteristics to emerge.

For Ethiopian Yirgacheffe, coffee farmers typically don't grade their beans by size for marketing purposes, unlike traditional countries mentioned earlier such as Brazil, Mandheling, and Colombia. Ethiopian coffee comes in various sizes, with only defective beans that would introduce undesirable flavors being removed. The variation in bean size is usually indicated by labeling them as "Heirloom" varieties.

FrontStreet Coffee often mentions in articles that Ethiopian beans vary in size. During roasting, to ensure larger beans are properly roasted without scorching the smaller ones, a safer approach is to drop them as quickly as possible. Some might ask, "Can't skilled roasters achieve even roasting?" The inherent woody structure of coffee beans determines their slow heat conductivity. When size differences between large and small beans are significant, this thermal conductivity cannot achieve even heat transfer. Although it's possible to reduce heat after dehydration and slowly extend the roasting time—this "boiling the frog slowly" approach can make the beans appear uniformly colored in terms of color, the aromatic characteristics inevitably become bland due to excessive roasting time. This represents another form of trade-off. For the floral and fruity acidic notes of Ethiopian beans, FrontStreet Coffee, like most roasters, chooses light roasting.

Take Geisha as another example—its floral and fruity characteristics distinguish it from most other coffee varieties. Many reviewers attribute these characteristics to light-medium roasting. Geisha varieties have a characteristic elongated shape that gives them greater volume compared to some varieties, especially Ethiopian beans which are already recognized as light-roasted. Two or three small Ethiopian beans might barely match the size of one Geisha bean. Regardless of preference, its roasting requires more time. From another roasting principle perspective, roasting as much as possible without creating scorching bitterness produces more aromatic qualities and leads to greater flavor complexity—this represents the pursuit of roasting.

Whether for roasters or drinkers, different people have different understandings and perspectives on coffee. Sometimes there may be no completely standard answers—only different choices.

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