Last year, another green coffee importer’s monthly newsletter included an article extolling the benefits of air roasters. Given our emphasis on espresso and balanced coffees, we’ve typically been less enthusiastic about air roasting than many others in the industry.  

Below is response that Dr John, our President and founder, submitted:

I read with interest your article entitled “Roasting with Hot Air: Benefits of Air Roasters” in your company’s newsletter.  

In summarizing the benefit of air roasters, you seemed to mention rather casually, “There is a direct relationship between increased air flow and crisp acidic profiles in the cup, and air roasters accentuate that relationship.” I happen to believe that these two characteristics need to be stated with more emphasis and perhaps elaborated with greater details. 

In the air roasters I have experience with, such as Sivetz roasters, they are single pass systems, in that the pre-heated air passes only once over the coffee beans being roasted. All the byproduct gases produced during the roasting process are immediately removed from the machine; resulting in “clean, pure coffee flavors.” 

In drum roasters, the hot air and the gases produced during the roasting process are retained in the roaster for a period of time and recirculated. The coffee beans end up absorbing some of the flavors from the contaminated air and display in the cup what I describe as “roaster flavors.” 

Regardless of how heat is applied to the outside of the beans, heat reaches the insides of the beans by conduction. And, when it comes to heat conduction, coffee beans are not very good at it. Therefore the development of the insides of the beans always trails the development of the outsides of the beans. 

Air roasters tend to run hotter and the outsides of the beans develop to the desired level in as little as 4 minutes and seldom longer than 11 minutes. Drum roasters tend to take longer to develop to the same degree, taking from 12 to 18 minutes. 

When roasting times are low, the insides of the beans fall so far behind so as to be mostly un-roasted or under-roasted when the outside looks perfectly roasted. Cup testing seems to record high acidity, but is really the green, grassy taste of un-roasted portion of the beans. This is being misinterpreted as high acidity. 

For brewed coffee this apparent highly acidity can be treated as a virtue. When coffees that have been air roasted are used for espresso, there is a serious problem. A coffee or a blend used to brew coffee and rates a score of 9 on a scale of 1 to 10 for its acidity, will have its acidity go completely off scale when it is made at five times the strength of brewed coffee in making an espresso.