Air Roasting Coffee
UPDATED :
Challenging our assumptions is always a good thing. A few years ago, I was in an SCAA Skill Building subcommittee reviewing the curriculum for the introductory espresso classes.
"Espresso" was defined in our SCAA curriculum for years with extraction time s between 18-23 seconds.
However, excellent baristas in the World Barista Championship competition were regularly extracting longer— in some cases, way longer—pours.
It seemed that it was time to redefine the length of pour time. "Can we change the definition of espresso?" questioned one of the members. After all, this was in writing and stood as a truth in the industry.
But it wasn't what leaders in coffee were producing as great espresso.
It was time to change. We rewrote the guideline and sent it to Statistics and Standards to confirm—the definition has been revised to a range of 20-30 seconds.
Is it time to reassess standards in roasting?
Before we dive in to answer that question, let's establish a few important definitions:
DRUM ROASTING COFFEE BEANS
The most common method of roasting and the style of most commercial roasters. These roasters feature a rotating cylindrical drum, to which heat is applied—either directly under the drum, or centrally through a conduit. Drum roasters can use electric or gas heat and utilize a combination of convection and conduction.
AIR ROASTING COFFEE BEANS
Also called fluid bed roasting, this method is more common in home and sample roasters. Systems feature a tall cylinder through which hot air flows, providing homogenous distribution of heat.
Fluid bed roasters rely completely on convection. The first air roaster was patented by Michael Sivetz, who firmly advocated for a higher-quality cup yielded by his design.
PROFILE ROASTING COFFEE BEANS
Varying temperature over the period of roast time produces different results. Each green coffee has a distinct chemical makeup due to coffee bean variety, growing region, and processing method.
Coffee roasters seek to reveal characteristics of each coffee by controlling the chemical reactions that occur during the roast process.
In drum roasting, the roast master is also controlling variables of air velocity and gas pressure.
A long-held assumption in traditional drum roasting is that the balance between conduction and convection airflow is key to roast development. Fluid bed roasting, or air roasting, heats only by convection.
How does this affect roasting development and the quality of the final result? Is the balance between convection and conduction needed for good specialty coffee?
A small fluid bed roaster, now available with profile roasting control, facilitated comparisons that could test these questions.
The Sonofresco Profile Roaster (with Advanced Definition Roasting technology) is only available in one - and two-pound batch sizes, but allows mirroring the roast profile (temperature over time) that someone roasting on a drum profile has determined to be their favored roast.
By isolating development time and comparing the roasted results across the two types of roasters, the hope is to closer examine the effect of combination convection and conduction—versus pure convection—on sensory outcomes.
These types of comparison tests are by no means definitive, but are intended to motivate others to perform more comprehensive testing on the subject.
Profile drum roasting has been an industry standard in specialty coffee for over a decade; profile roasting with air roasters is much newer.
It's generally assumed that drum roasters, balancing conduction and convection, yield more body, and air roasting can achieve more sweetness and brightness.
These assumptions made the opportunity to test the same profile of drum roasters with an air roaster all the more enticing. By controlling the ramp-up temperature against time, profiles can be duplicated from drum to air roaster.
This allows us to isolate differences between convection and conduction, rather than arguing the drum versus air issue.
The work started with some comparisons that Willem Boot of Boot Coffee Consulting did in 2013 and documented on video.
He started with two different coffees, roasting each green variety to his optimum target on a one-pound San Franciscan drum roaster.
The same roasting profile was set on a two-pound Profile ADR Sonofresco. His resulting videos are worth watching.
I recruited some great roasters to help conduct similar tests.
I collected data and results from Caffe Ladro, Nossa Familia, Klatch Coffee, Just Love Coffee, King Coffee, Doma, Torque, Tony's Coffee, and Nobletree.
To expand on Willem Boot's experiment, I asked each roaster to use two coffees they roasted regularly, using a roasting profile they were familiar with. I also asked them to compare air-roasted results with drum-roasted results.
We set out to isolate as many extraneous variables as possible in roasting, stripping everything possible away except the comparison of drum and air.
In short, many roasters noted more brightness, less body, and more flavor in the air-roasted samples compared to the drum-roasted.
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