What is Air Roasting?
Air Roasting is a method of roasting coffee beans with a hot air current. In this technique, the beans are roasted by being suspended in the air without a drum by a strong hot air current given from below. The fact that the beans remain freely suspended in the hot air allows the heat to be distributed equally to each bean and prevents surface burns that can be seen in drum roasting. Therefore, since the beans do not come into direct contact with the hot metal surface during air roasting , an even and gentle roasting takes place. This method highlights the natural characteristic aromas of the coffee beans; the resulting coffee is usually clean, bright, acidic and has nuanced flavors . In addition, in air roasting, the chaff is separated from the beans by a continuous air current and thrown out during roasting. In this way, smoke and burnt particles that can occur in drum roasting are prevented from coming into contact with the coffee, and unwanted sooty or bitter flavors in the coffee are minimized.
The air roasting system was first popularized by Michael Sivetz in the 1970s and is also known as the “fluid-bed roaster.” Today, there are commercial air roasters in the industry that operate on the fluid-bed principle. Air roasting is especially common among small-scale roasters and innovative coffee producers. However, the majority of coffee roasted worldwide is still processed in drum roasters (an estimated 90% or more). However, air roasting has gained attention in the specialty coffee sector due to the clean and bright flavor profile it provides, and has become preferred by some boutique roasters. In the industry, air roasting is also being evaluated, especially in operations requiring high capacity or in continuous roasting lines, due to its fast roasting and energy efficiency advantages.
Figure 1: Air roasting principle – The beans are held in a bed of air by a hot air flow from below and roasted evenly. This fluid-bed system keeps the beans in constant motion, eliminating the need for mechanical mixing as required in drum roasting. (Barista Hustle)
Comparison with Traditional Roasting Methods
We can compare air roasting with traditional drum roasting and other convection roasting systems in several aspects:
Heat Transfer and Roasting Technique: In drum roasters, heat is transferred to the beans by conduction from the walls of the rotating metal drum and convection from the hot air inside the drum. Radiation from the hot surfaces also contributes to some extent. In contrast, air roasting is based entirely on heat transfer by hot air flow ( convection ); the beans do not come into direct contact with the metal surface because they float in the hot air.
As a result, in air roasting, the heat distribution is more homogeneous and reaches each bean equally; in the drum method, some bean surfaces may come into contact with the drum and receive more heat (if not mixed properly, spot burns may occur). In convection systems (e.g. fluidized-bed or hot air blast roasters), there is similar heating by air flow, but air roasting uses this principle to its maximum.
Roasting Time and Heat Profile: Air roasting is generally characterized by shorter roasting times . Thanks to the strong airflow, heat transfer is very effective and the internal temperature of the bean increases rapidly. As a result, a batch roasting time can be shorter compared to a drum roaster. For example, in fluid-bed systems, a light/medium roast can be completed in as little as 5–7 minutes under suitable conditions, while in drum roasters, roasting with a similar profile usually takes 10–15 minutes (may vary depending on the roaster's preference). Applying high heat in a short time increases production capacity and offers the opportunity to roast more coffee per hour. In drum roasting, the roasting time is longer and more controlled; this allows the internal structure of the bean to heat gradually. Heat profile control in both methods is possible with the appropriate equipment and sensors, but traditionally in drum roasters, roasters can follow a slower and more developing roasting curve, relying on the heat stability of the drum.
Energy Efficiency: Since air roasting transfers heat directly to the beans via air and there is no need to constantly heat a heavy drum, the heating efficiency is considered high . Since the hot air flow touches the beans from all surfaces, fast results are obtained from the given energy. However, since this system requires continuous air blowing with powerful fans, energy is spent for heating and circulating the air. Modern air roasters try to save energy by recirculating this air. In drum systems, the energy cost may be slightly higher due to the heating of the heavy metal drum and heat losses; however, since the heat inside the drum is also better preserved, efficiency can be achieved in well-insulated machines. In general, air roasting carries less inert heat mass and has the advantage of rapid heating/cooling in this respect.
Roasting Capacity and Scalability: Traditional drum roasters are available in a wide range of capacities (from 1 kg to 120+ kg) and large-scale industrial roasters are usually drum roasters. Fluid-bed roasters are difficult to design above a certain capacity; they are generally limited to medium-sized batch sizes (<10-15 kg/batch) due to the high airflow requirements and even distribution difficulties. Therefore, drum (or hybrid convective) systems are preferred in large coffee factories. Air roasting is a practical solution for small and medium-sized businesses or micro roasters, but is not as common as drum roasters for very large batches.
Effects on the Physical Structure of the Coffee Bean: The roasting process significantly changes the internal structure of the bean (cellular structure, density, moisture content). The degree of these changes may vary depending on the method. Studies have shown that there are systematic differences in the moisture and density values of coffees roasted in different roasting machines. For example, in a study comparing the same coffee roasted with a drum roaster and a hot-air roaster, the moisture content and density of the beans roasted in the drum were found to be higher , while the air roasted beans were lower. This can be explained by the fact that the beans lose water more quickly and expand more in the air roasting method. The sudden pressure created inside the bean as a result of rapid heat transfer can make the cell structure more porous and voluminous . In fact, in the same study, the color value (roasting darkness) of the beans in drum roasting was slightly higher compared to air roasting. The results of roasting with the convection (air flow) system generally showed values in between the two extremes. These data demonstrate that roasting method has measurable effects on the physical properties of the bean. These differences in cellular structure can also be reflected during milling and brewing; for example, fragmentation and extraction behavior will differ when milling more porous, lower-density beans.
The Effect of Air Roasting on the Aroma Structure of Coffee
The roasting method significantly shapes the final aroma and flavor profile of the coffee. Some differences have been reported between air roasting and traditional methods in terms of the formation and preservation of volatile and non-volatile components in coffee.
Aroma Compounds and Volatiles: Hundreds of volatile aroma compounds are produced during the roasting of coffee beans. The roasting technique can affect the profile and amount of these compounds. For example, a study on Robusta coffee examined the differences in volatile compounds between hot air roasting and drum roasting . While the two methods produced similar numbers of aroma compounds at a light roast level, drum roasting provided a significantly greater variety of volatile compounds at darker roasts. In the same experiment, 48 different volatile compounds were detected in coffee roasted with a drum roaster at a dark roast level, while only 18 compounds were detected in the equivalent coffee roasted with a hot air roaster. This result suggests that a longer, more traditional roasting process may produce a more complex profile in aroma development . In drum roasting, oils and aromatic compounds that rise to the outer surface of the beans may re-contact some of the smoke accumulated in the drum and penetrate the bean. In air roasting, on the other hand, because the strong air current rapidly removes these compounds, less smoky residue remains on the bean. For this reason, coffees that are air roasted usually exhibit a cleaner flavor profile ; acidity and unique aromatic notes are prominent, and smoky/incense aromas from roasting are minimal. In fact, the sector often emphasizes “brighter acidity, cleaner flavors” for coffees roasted with the air roast method.
Flavor Profile Differences (Body, Acidity, Sweetness): Flavor differences have also been reported between drum and air roasted coffees. Drum roasting can often give the coffee a fuller body and caramel/smoky notes from the roasted bean. Especially in medium and dark roasts, the body of the coffee can be pronounced with the drum method, while the bitterness can be controlled. Air roasting tends to preserve the acidity and the intrinsic sweetness of the bean; coffees roasted with this method exhibit a vibrant acidity and brighter, more pronounced flavor notes . For example, citrus, floral, or fruity aromas can be felt without being lost when air roasted. In terms of body, air roast coffees can be slightly lighter and smoother than their drum-roasted counterparts – this may be due to less Maillard-derived heavy compounds being formed during roasting, or due to the interior of the bean drying out too much, reducing flavor intensity. Some roasters claim that rapid roasting with air currents dries the inner parts of the bean quickly , reducing sweetness and acidity in the core , which is why air roasted coffees can be “thin-bodied and short-finished.” However, this disadvantage can be overcome with the right profiling. Ultimately, air roasting offers a flavor profile that reveals the original character of the bean without masking it ; while drum roasting adds complex flavors and fullness from the roast . Which profile is better depends on the desired coffee experience.
Effects on Coffee Extraction: The roasting method can also indirectly affect the interaction of the bean with water after it is ground. For example, beans with lower density and a crispy structure as a result of air roasting may show different extraction characteristics during water brewing. Thanks to their porous structure, they can absorb water quickly and release their components quickly, which can shorten the brewing time and create a higher extraction potential. On the other hand, air roasted coffees can release very intense gas immediately after they are freshly roasted (because CO2 is trapped inside in fast roasting), which can cause problems such as channeling in pressurized brews such as espresso. Drum roasted coffees generally offer more balanced gas release and extraction. For this reason, some baristas recommend letting air roast coffees rest a little longer (degassing) after roasting. However, the effect of the roasting method on extraction efficiency has not been studied thoroughly scientifically; the existing data is mostly in the form of sensory observations. Generally speaking, coffees roasted with the air roast method offer a clean cup of water, which is due to the fact that unwanted bitter components are not extracted during brewing. In quality coffee tasting notes, descriptions such as “bright acidity, clean finish” stand out for air roast, while descriptions such as “denser body, long finish” are heard for drum roast.
Findings from Academic Studies
Academic studies on air roasting and traditional roasting methods have demonstrated the chemical and sensory effects of these methods with quantitative data:
Physicochemical Components: A study examining the effects of different roasting methods on Arabica coffee found that changing the roasting method (drum vs. hot air) had significant effects on the acidity level and antioxidant activity of the coffee. The same study reported that antioxidant activity and chlorogenic acid levels were distributed differently in hot air roasted samples. This suggests that roasting technique may affect not only the taste but also the health-related components of coffee. On the other hand, caffeine content was not significantly affected by the change in roasting method. In both air roast and drum roast, caffeine levels in coffees roasted to the same roasting degree remained largely similar. Therefore, caffeine is a parameter that depends more on the roasting degree (light/medium/high) and does not show significant differences according to the method.
Moisture, Density and Colour: In a study conducted by S. Biswas and S. Das (2013), Robusta coffee beans were roasted with different roasting machines and their physical properties were compared. The results revealed that the drum roasted beans had the highest moisture content and density , while the hot air (fluid-bed) roasted beans had the lowest density and moisture . Similarly, in the colour analysis, it was observed that the drum roasted coffees were darker in colour (despite the same roasting profile), while air roasting gave a slightly lighter coloured product. These data confirm the structural differences mentioned in the previous sections. In addition, when the surface structure of the beans was examined microscopically, it was reported that more cracking and pore formation were observed in the cell walls of air roasted beans (due to rapid gas evolution). This may affect the particle size distribution and aroma release after grinding.
Volatile Aroma Compounds: There are also experimental studies on volatile compounds that determine the aroma profile of coffee. In a 2023 study mentioned above, aroma compounds produced by drum and fluidized-bed roasters at light, medium and dark roasting levels in Robusta coffee were compared. While there was no significant difference between the methods in light roasting, drum roasting revealed a much richer volatile compound profile compared to air roasting in medium and dark roasting. It is particularly striking that 48 different volatiles were detected in coffee roasted with the drum method at the medium roasting level, while only ~20 compounds were detected in air roast coffee at the same level. The researchers stated that this may be related to the rapid removal of volatile compounds and the short contact time during air roasting. In drum roasting, some compounds may have been retained in the bean due to longer exposure and smoke circulation. However, it was observed that the number of volatile compounds decreased in both methods as the degree of roasting increased (for example, as dark roasting was achieved); because excessive heat breaks down many aromatic compounds or reduces them to similar carbonization products.
Sensory Evaluations (Tasting Tests): Blind tasting tests conducted to evaluate the effects of different roasting techniques on taste are also included in the literature. For example, in a study conducted in 2017, Robusta coffees prepared with drum, hot air and hybrid convection roasting were compared sensorily by panelists. The results showed that drum roasted coffee received the highest average score in aromatic intensity, body and overall liking criteria, followed by the convection system and the lowest by the air roasting method. In this study, the fact that drum roast coffees were found to be “more balanced and closer to traditional coffee flavor”, while air roast coffees were described as “lighter and have distinctive flavors but are unusual by some panelists” suggests that consumer habits may also play a role. Since the common coffee flavor is identified with drum roasting. In fact, one roaster with 20+ years of experience says that because the vast majority of coffee roasted worldwide is drum roasted, the “standard coffee flavor” consumers are accustomed to is the drum roast profile. This standard profile often includes caramelized sugars and subtle smoky nuances, while fluid-bed roasting can be brighter but less unusual. Taste tests have also shown that air roasts score high on acidity, but can be lower on body. Of course, these are general trends, and results may vary for each bean and roast profile; while an educated panel may appreciate the floral notes that air roasting brings, some consumers may find the darker tones they are accustomed to lacking.
Conclusion and Recommendations
Which Method is Suitable for Which Coffee?
The choice between air roasting and drum roasting largely depends on the type of coffee to be roasted and the desired flavor profile . To summarize, coffees roasted with the air roasting method are brightly acidic, aromatically clean and complex in structure, preserving the origin character of the bean to the maximum extent . Therefore, air roasting can be a good option for single-origin Arabica coffees, especially when fruity or floral aromas are desired to be emphasized. In addition, the absence of bitter burnt flavors during roasting provides the desired clarity, for example in lightly roasted coffee profiles. On the other hand, the drum roasting method is advantageous when a more full-bodied and classic cup is desired. For consumers who like dark roasts or want a strong profile that will not lose its flavor even when mixed with milk in espresso, the roasted tones obtained with drum roasting (caramel, chocolate, hazelnut and slightly smoky notes) can be more satisfying. For example, drum roasting is mostly preferred for Robusta or blends with high body and bitterness; Indeed, some studies have shown that robusta beans are more sensorially acceptable when drum roasted. This may be related to the drum method softening the harsh character of robusta and giving it a more “coffee-like” profile.
The Future of Air Roasting and Areas for Development: Air roasting has an important place in coffee roasting technology with its clean flavor profile and efficiency advantages. In the future, it is expected that some of the limitations of this method will be overcome with technological innovations. Especially large-volume air roaster designs are being equipped with more sensitive airflow and heat control sensors to solve the scale problem. In fact, today, some modern air roaster manufacturers have started to develop machines that can reach 15+ kg capacity and can apply sensitive profiles with software. In addition, methods such as heat recovery and partial gas circulation are being tried to prevent the aromas formed during air roasting from completely escaping - thus both energy saving and flavor optimization are aimed. Another area of development is the issue of error tolerance . Since air roasting is a fast process, the operator or automation must provide very good control; in the future, it will be possible to keep roasting profiles on the ideal course by receiving instant feedback with artificial intelligence-based control systems.
Commercial Roasters and Best Practices: Regardless of the method used, the roaster’s goal is to bring out the best in the bean. As a best practice , if drum roasting is used, the machine should provide sufficient airflow to prevent smoke accumulation, and drum loading and mixing should be optimized to roast the beans evenly. If air roasting is used, the strength and temperature of the airflow should be adjusted according to the bean size and density, and the fan speed curve should be well managed to prevent the beans from becoming lighter and flying away towards the end of the roasting. Qualified coffee roasters can try both types of roasters if possible to determine the profile that best suits their coffee and their customer base. It should not be forgotten that the best coffee is ultimately the one that appeals to personal taste. While drum roasters offer classic and established flavors, air roasters offer new and bright experiences. It is possible to produce excellent coffees with both methods with skill and attention. The important thing is to keep the roasting process under control, taking into account scientific findings and technical principles, and to evaluate quality by constant tasting.
In conclusion, Air Roasting and traditional drum roasting methods each offer their own unique advantages. Air roasting brightens the natural flavors of the coffee with rapid and uniform heating, while drum roasting creates deep and full-bodied flavors with slow development. Coffee professionals should choose these methods and their variations according to the type of coffee and the desired profile, aiming for the best cup in the light of scientific data. Academic studies in this field will contribute to the development of more conscious and creative roasting techniques in the future by providing a better understanding of the effects of roasting technologies on coffee chemistry and quality.
D.EMRE KURTULUS