How do different coffee roasters affect the flavor of coffee?

Roasting is a crucial stage where coffee beans release the tightly held aromas within. Through heat, various chemical reactions occur, creating the aroma and flavor of coffee. Particularly, two important reactions need mentioning: the Maillard reaction and caramelization.

The Maillard reaction can form Melanoidins – a dark brown compound with roasted, malt, bitter, pungent flavors, contributing to the robust flavor of coffee. On the other hand, caramelization breaks down long, complex carbohydrate chains into hundreds of new, smaller compounds, adding significant bitterness, acidity, and aroma to the brew.

Coffee roasters can utilize various roasting machines depending on their characteristics, purposes, and preferences. Among them, two popular types of roasters are drum roasters and fluid bed (or air) roasters.

Drum roasters

This machine operates by heating a rotating drum. Coffee beans are heated through both heat conduction from the drum’s surface and convective heat transfer from the surrounding air. Its advantage lies in producing evenly dark-colored roasted coffee batches. However, using it requires skill because coffee beans in contact with the drum may risk burning.

* Single Drum Roaster

This is a typical type of drum roaster. Its structure includes a burner at the bottom to heat the drum as it rotates, and the drum transfers heat to warm the coffee beans. This type of machine often produces uneven roasts due to heat retention in the drum.

* Double Drum Roaster

This refined roaster employs air between two layers of drums as insulation. Consequently, coffee beans can receive more convective heat. This technology allows for better temperature control during roasting, resulting in more even roasts and reducing the number of scorched coffee beans.

* Perforated Drum Roaster

Perforated drums enable more convective heat transfer during roasting. Through this enhanced airflow, the roaster can produce more even and flexible batches. Additionally, the roasting process with perforated drum roasters consumes less heat compared to traditional drum roasters

Fluid bed roasters

Compared to drum roasters, fluid bed roasters roast coffee faster, consume less electricity, and are suitable for lighter roasts. They tend to preserve the coffee’s harmony and characteristic acidity better because they rely solely on a stream of hot air to roast the coffee beans: the air is preheated and then pushed through a chamber containing the coffee beans. This airflow suspends the coffee beans on a “layer” of hot air. However, due to their more complex structure, fluid bed roasters are more expensive and challenging to maintain, especially with limited capacity. It’s essential to note that most fluid bed roasters do not offer the option to check the coffee beans during the roasting process.

Different types of roasters with varying structures and features will uniquely impact the flavor development of coffee beans. Therefore, roasters need to understand the operating principles of their machines to adjust the parameters so that the coffee beans are guided correctly, preserving their inherent characteristics. The most apparent difference is that drum roasters made of cast iron or steel retain heat longer than fluid bed roasters. This means you’ll need to use less heat in the later stages of the roasting process because most of the initial heat emitted in the early stages will be retained throughout the entire roasting process.

The different heat distribution methods of various coffee roasting machines will affect the overall sensory experience because they transfer heat to the coffee beans differently. Therefore, roasters need to control airflow accurately to avoid burning the beans. Different roasting machines combined with different brewing methods can yield a relatively diverse range of flavors. With filter or espresso brewing methods, coffee beans roasted with drum roasters tend to produce sweeter flavors, while the flavor profiles become clearer compared to indirectly heated roasters.

We can say that different types of roasting machines can highlight certain flavor characteristics. Indirect heat roasters provide a clean taste and are suitable for high SCA score beans with a lot of sweetness and acidity, while also easily accentuating any flaws in the beans. Additionally:

– Gas-powered roasters have higher heat transfer efficiency and faster reactions compared to electric ones, which enhance the acidity inside the beans. Electric roasters, on the other hand, distribute heat more evenly, increasing sweetness and fullness.

– For drum roasters, slower speeds and higher airflow can result in more even roasts and enhance complex flavors. Faster drum speeds and lower airflow create brighter acidity and enhance fruity notes.

– With fluid bed roasters, higher airflow and increased agitation can produce lighter roasts and brighter acidity, while lower airflow and less agitation result in darker roasts with more chocolate and nutty flavors.

Although different roasting machines approach coffee beans differently, they are only tools for roasters to develop the flavor of the beans without directly determining the flavor notes or bean quality. This depends on the experience and expertise of the roaster. Therefore, by understanding the characteristics and operation of each machine, skilled roasters can overcome limitations and create fully aromatic and flavorful batches of coffee.

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