Nuances of Coffee Roasting – Dilworth Coffee

Roasting coffee is a complex mix of art and science. We caught up with Brad Kirby, our Director of Coffee, between roasting coffee batches on his 60-kilo roaster and asked him a few questions.

Can you explain a bit about Dilworth Coffee’s roasting philosophy?

At Dilworth Coffee, our goal is to present all coffees in a way that shows off the best of what they have to offer. We also consider what the customers have told us they like. We experiment with each bean to determine what roast level is best for each varietal and blend.

You roast some coffees light and others dark, correct?

Yes. When we roast a coffee that’s dark, we do it in such a way that still has some nuance to it as best we can. When we’re talking about some of our medium and light roasts, we’re striving for maybe a little more development than a lot of roasters. And when I say a lot of rosters, I’m talking about your smaller, higher-end third wave-kind of roasters. A lot of those folks would not consider roasting some coffee as far as we do. But we don’t take anything past second crack. We roast a couple of coffees to second crack for some customers, or for like our French roast, San Remo espresso blend or organic Sumatra because people who buy those want that dark coffee flavor. We’re striving to get coffee roasted in a certain time for each coffee so we don’t over roast and bake flavors out. We’re not rushing it, though. We stretch some of that development time out to get a little more depth. 

How much does technology assist you?

The computer is our consistency tool. It will guide the gas valve and take readings from the temperature probe, but it’s up to us to charge the roaster to the right temperature. That changes a lot throughout the day depending upon how hot the roaster is, how many roasts we’ve done or the particular bean and the density of it (that’s one of the larger considerations). Every coffee has its own set of parameters for its profile. To hit all of them, we take these other points into consideration. If we, as a roasting staff, don’t do that right the computer isn’t very helpful at all; other than it won’t let you burn a batch up because it beeps at you and tells you it’s time to get the coffee out. It does have a failsafe and will open when a certain temperature is reached, so you can’t really leave beans in there until they turn to charcoal.

How do you know the proper temperature at which to roast?

We set the temperatures for each roast; each has parameters with a couple of temperature points along the curve that allow the algorithm to compute that curve. We roast enough here so that every profile gets used several times per week so we’re pretty confident on those final temperatures. I like the roaster (the person) to verify each roast and visually look at them. Generally, we try to make sure it’s hitting its points and then let the roaster open at the final temp.

 What is one the challenges in the roasting process?

The main thing we’ve got to do is load the right amount of beans and then judge the proper charge temperature for each type of bean. If you drop a mass of room temperature beans into a hot roaster, temperature plummets. At some point, there is an equalization where the profile curve bottoms out. That is something I’ve taught our staff; we want to bottom out in a pretty small range at a specific temperature and in a specific time for each bean.

So each varietal roasts differently?

Absolutely. Every little bean presents its own set of problems. Some are hard and big, some are hard and small, and some are soft. You don’t charge the roaster for a nice delicate Ethiopian the same as you do for a hard Guatemalan. They each require different inputs since they have different profiles. Our experience allows us to determine what is best for each bean.

For more information about our coffees, please call 866 849 1682 or email