Applying the Right Heat for the Bean

In coffee roasting, there isn’t a single formula or method that you can call “tried and true”. The variables are numerous, and knowing how to address each variety of coffee is what makes a roastmaster. In How Roasting Style Changes the Flavor of Coffee, I discussed how a faster application of heat can lead to sweeter flavors with more clarity. While this might be desirable for some varieties of coffees, for others it can ruin them!

How quickly a coffee bean will absorb heat is partly determined by its density. Beans that are grown at higher altitudes with wider variations in temperature between daytime and nighttime tend to be more dense than beans grown at lower altitudes and in more steady climates. Heat absorption is also influenced by the way a coffee bean is processed. “Wet Processing” results in a higher consistency from coffee bean to coffee bean because it’s possible to use the process to cull out beans that are of lower density (often due to being less fully developed) from those that are more dense. A more consistent bag of beans will roast more evenly, even when heat is applied rapidly.

The example roast shown in this post is a lower altitude Yellow Bourbon from the Mogiana region of Brazil. This is a wonderful-tasting coffee but for the roaster it presents two challenges. It is both lower in density and natural processed. These beans are too sensitive and inconsistent to apply the “fast heat for sweetness” approach as demonstrated by the two example roasts shown. Both were “finished” at 415°F. The roast on the left uses a lower charge temperature and a slower application of heat with higher airflow. The total roast time was 14:30. As a result, the roast is very even and consistent, even though there is a certain amount of variability in the coffee beans. The roast on the right had a faster application of heat with lower airflow, meaning more heat was absorbed through conduction (physical contact with the roasting drum) than convection (heated air bathing the beans) and finishing at a faster 13:10.

You can see in the example that the faster roast, which would have been a winner for a Colombian or Kenyan coffee, produced a terrible result. Some beans are under-roasted, others show burnt spots and oil emerging on the surface. By appearance, you would think that someone blended two or three very different roasts, but this is not the case. It is simply a excess of convection heat, applied too rapidly, has stretched the inconsistencies in this particular batch of beans to the point of making a coffee that might go over well with those who like the Starbuck’s flavor, but would be considered garbage by third-wave coffee fans. In truth, it’s an interesting taste, combining the smokey qualities of a dark roast with sweeter notes of a light-medium roast. I’m sure it will have some fans were I to share this batch, but I would never produce a roast like this intentionally, other than to demonstrate how to produce an inconsistent roast.

One of our goals at Evansville Coffee Company is to create the best possible single origin and blended coffees from some of the best coffees available. We won’t diminish that goal with a less-than-remarkable coffee, so when you try our Yellow Bourbon, you can be sure we will use the slower, high-airflow roasting profile we developed for this coffee.


How Roasting Style Changes the Flavor of Coffee

You might be surprised to learn that the way a coffee is roasted can have a huge impact on the flavor. And we’re not talking about air roasting versus drum roasting, or home roasting versus commercial–different roasting styles that influence coffee flavor can be performed on any roasting equipment. Roasting coffee is as much an art as it is a craft, and one of the important variables that a master roaster has at their disposal is the application of heat. Or more specifically, how quickly or slowly to allow coffee beans to absorb heat.

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One Bean, Two Roasts, 15° Difference

I roasted a couple sample batches today from a small estate in the Carmo de Minas region of Brazil. The beans were a gift for a friend, but I rarely pass up the opportunity to probe for changes based on single variables. If you don’t want to “geek out” on coffee science, you might as well quit reading now, and enjoy a latte, because this is going to be a heady and opinionated entry in the notebook.

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I Just Bought a Commercial Roaster!

When I started sharing my coffee with friends, the first thing they would ask is “Can I buy it”? The problem with my HotTop roaster is while it’s great for evaluating beans with different roast profiles, it’s not a money-maker. At 1/2 lb. per roast, and a minimum of 20 minutes invested in each roast, the best I can expect to produce is 1.5 lbs. per hour. You can do the math, but the conclusion is that my roaster needs to be at least 10x more efficient to be viable as a business. Read more

Nice dark roasted coffee

Reflections of an Amateur Coffee Roaster

When I set out to roast coffee for myself, I had no idea how much joy would come from it. For one thing, the quality of coffee I have been drinking has vastly improved. I had settled into a routine. I bought espresso roasts from a few of my favorite sources, including Staufs Coffee Roasters and Lighthouse Roasters. Because of the cost, I decided to limit myself to just a couple of “Americanos” per day, making a pound of coffee last around 12 days. It was a self-imposed exile. Read more

Computer Driven Roasting

Since upgrading my HotTop drum roaster to the “latest and greatest” B2k+ controls, I now have a USB port that plugs into my laptop computer for both recording roasts, and designing roast profiles that I can then send to the roaster. I still manually charge the beans and monitor the roast, and can make adjustments on-the-fly if I wish, but I can also run a roast in “full auto mode” and as long as I drop at the same environmental temperature, things will stick pretty close to the original plan, within a few degrees. Read more

Why Micro-Roasting Produces Better Coffee

You might think all this fuss about micro-roasting and specialty coffee is awesome idea or you might think it’s just making the best case for a business that is too small to compete with the big guys. While it’s certainly possible for larger companies to produce some outstanding coffees and for the little guys to produce a cup that is, umm, shall we say, “uninspired”, a coffee roaster who truly cares about the quality of their final product has much greater potential for producing a cup of coffee that is head and shoulders above what the larger companies can ever hope to achieve. And this is because of some very practical reasons. Read more

The Evolution of Roasting Styles

Although coffee has been around for hundreds of years, many changes have occurred over the past two decades. Originally, people roasted their own coffee, often using a hand-powered roaster that would be set over a flame. With the introduction of packaged products, roasted coffee quickly became a convenient and time-saving item to purchase. Instant coffees […]

Learning to Roast Coffee

I’ve been drinking quality coffee since the early 1980’s when my housemates and I would buy fresh roasted beans and grind them with a hand grinder, and using a Melitta pour-over cone and filter. When I visited Boston for the first time in 1983, I discovered french press coffee at The Coffee Connection in Harvard […]