Coffee roasting is a process that transforms the physical and chemical properties of coffee beans into the roasted coffee products we all know and love. The roasting method used can have a significant impact on the final flavor, aroma, acidity, body, and other characteristics of the coffee. In recent years, air roasting has emerged as an alternative to traditional conductive heat roasting, and is growing in popularity among specialty coffee roasters and connoisseurs.
What is air roasting?
Air roasting, also known as convection roasting, uses hot air rather than conductive surfaces to heat and roast coffee beans. In an air roaster, a powerful fan circulates high-velocity hot air at temperatures typically between 375-550°F around the coffee beans to facilitate even and efficient heat transfer.
This differs from conventional conductive heat drum or plate roasters that roast beans through direct contact with a very hot metallic surface. In conductive roasting, heat is transferred from the hot surface to the beans through conduction, with the beans closest to the surface getting hottest while those on the interior taking longer to heat up.
Benefits of Air Roasting
There are several potential advantages to roasting coffee with hot air rather than conductive surfaces:
More Even Roasting
The turbulent hot air flow in an air roaster promotes very uniform heating of the coffee beans. The constant motion of beans in the roasting chamber ensures even exposure to heat rather than having some beans closer to the heat source while others are further away. This can lead to a more consistent roast level within a batch.
Better Heat Control
Conductive heat roasting relies on adjusting burner temperature and roast time to control the rate and degree of heating. Air roasters provide more precise control over the roast by modulating the heat and airflow. If needed, the roaster can quickly reduce air temperature or velocity to prevent over-roasting.
Lower Risk of Burning
With conductive heat roasting, especially drum roasting, beans can come into direct contact with very hot metal surfaces of over 500°F. This runs the risk of scorching or burning some beans. The constant air circulation of an air roaster avoids direct contact between beans and hot surfaces.
Shorter Roast Times
The turbulent forced airflow allows for very efficient heat transfer into the beans, typically decreasing total roast time by 2-4 minutes compared to conductive roasting. Shorter roasts minimize the breakdown of flavor compounds in the beans.
Better Environmental Control
Air roasters provide greater control over the bean environment during roasting. The airflow rate, temperature, and even atmospheric pressure inside the roasting chamber can be modulated. This allows for profiling and adjusting the environment during different stages of the roast.
Easier Cleaning
Air roasters do not have some of the hard-to-access surfaces and crevices that can collect oil and residue in conductive drum roasters. The smooth stainless steel construction and lack of internal protuberances make cleaning easier.
Space Savings
Air roasters take up less space than traditional drum roasters of equivalent capacity. Their compact footprint makes them ideal when space is limited.
Potential Drawbacks of Air Roasting
Despite the advantages, air roasting also comes with some potential downsides:
Higher Initial Cost
Industrial air coffee roasters currently cost significantly more than comparable capacity drum roasters. The advanced airflow and temperature controls add to the manufacturing costs. However, over the long run the increased control and efficiency can pay back the premium price.
Complex Controls
While conductive heat drum roasters rely on basic time and temperature parameters, air roasters require sophisticated electronics and software to control variables like fan speed, temperature, and airflow routing. This makes the roasting process less intuitive and requires technical expertise.
Less Equipment Choice
Drum roasters have been manufactured for over a century while air roasting only gained traction in the 1990s. As a newer technology there are fewer equipment manufacturers and options to choose from compared to the wide range of drum roaster makes and models.
Quieter Operation
The rotating drum and stirring paddles of conductive heat roasters provide auditory cues about the roast progress from first crack onwards. Air roasters run much quieter, removing this useful roast monitoring indicator.
Shorter Roast = Less Development Time
While air roasting decreases overall roast duration, some argue this provides less time for important chemical reactions to develop full coffee flavor compared to longer low-and-slow drum roasting. However, others contend that equivalent chemical development can occur faster at the higher air temperatures.
How Does Air Roasting Actually Affect Coffee Flavor?
The key question around the impact of the roasting method on coffee quality is how air vs. conductive heat roasting affects the flavor, aroma, mouthfeel, and other taste attributes of the final product. Let’s examine some of the evidence:
Volatile Organic Compounds (VOCs)
Volatile compounds are critical for coffee aroma and flavor. Studies have compared the retention and generation of VOCs between air and conductive heat roasting using gas chromatography. The results showed that air roasting lead to higher preservation of aromatic compounds present in green coffee beans, but also generated fewer new VOCs through Maillard and caramelization reactions compared to drum roasting.
Chlorogenic Acids
Chlorogenic acids are antioxidants found in green coffee that break down during roasting. High levels of chlorogenic preservation indicates reduced roast intensity. In comparative studies, air roasted coffees retained significantly higher concentrations of key chlorogenic acid compounds such as 5-caffeoylquinic acid.
Melanoidins
Melanoidins are brown nitrogenous polymers produced during the late Maillard phase of roasting that contribute to flavor, aroma, and color. Analysis shows air roasted beans contain less melanoidins compared to conductive roasting, indicating a lower level roast intensity.
Sensory Analysis
In cupping and sensory analysis by professional tasters, air roasted coffees consistently exhibit more acidity, fruitiness, and floral character. The less intense roasting avoids roasting out or masking some delicate flavors and aromas. However, air roasted coffees are also commonly described as having slightly less body.
| Attribute | Air Roast | Drum Roast |
|---|---|---|
| Acidity | Higher | Lower |
| Fruitiness | Higher | Lower |
| Floral notes | More | Fewer |
| Roasted/caramel notes | Less | More |
| Body | Lighter | Fuller |
Should You Air Roast Your Coffee?
So should you switch from your trusty drum roaster to an air roaster? Here are some factors to consider in making the decision:
Your Desired Flavor Profile
Air roasting excels at preserving delicate flavors like fruits and flowers but produces less of the deeper roast flavors. Choose air if you want light, bright, fruity coffees or drum for more chocolatey, caramelly dark roasts.
Your Green Coffee
Air roasting works best with high-quality, high-aciduity green coffee featuring nice inherent floral and fruity qualities you want to preserve. Lower-grade coffee with unremarkable green character is less suited.
Your Roast Skills
Air roasters require proficiency with sophisticated controls and electronics. For less technically adept roasters, a basic drum machine may be better.
Your Customers
While air roasted coffees rate highly among seasoned coffee pros, they may be too light and lack the full body that some retail coffee drinkers are accustomed to. Know your customers’ tastes.
Your Budget
The high equipment cost of quality air roasters is prohibitive for some. But if you have the capital to invest upfront, the potential quality gains could justify the expense.
The Verdict
When executed with skill and care, air roasting allows the true subtle character of high quality coffee beans to shine. The less aggressive roast provides a lightness and transparency of flavor, aroma, acidity, and origin character that drum roasting can obscure. While not ideal for every coffee or roaster, specialty coffee producers looking to create exceptionally nuanced and floral coffees will benefit greatly from adopting air roasting.