Roasting Washed Coffees from Ethiopia
Roasting coffees from Ethiopia can be incredibly tricky. While they are dense coffees, the beans are also a good deal smaller than other varieties (15+ screen) and they can behave rather delicately in the roaster. There can also be a great variability to the bean size in a coffee from Ethiopia as compared to a Kenya, Colombian, or Central American coffee. And not only does the bean behave delicately, but the flavors that you're trying to develop in the coffee are also delicate. This is not a coffee that you can bully with intense heat or one that will forgive you like a Kenya. Roasting Ethiopian coffees well is as much as a finesse game as there is in coffee roasting.
The quintessential cup qualities of the best Ethiopian coffees are the sweet floral notes, followed by the potent citrus notes. It's important to keep your eyes on the prize of the florals though, as many roasters get hung up on the lemongrass and citrus and end up roasting to that while burying the beautiful jasmine and honeysuckle notes. In some, the citrus and floral notes are perfectly married into bergamot. Ethiopian coffees are not for deeper roasting.
Getting into Full City on an Ethiopian coffee might help push some of the gingery or clove spice notes, but chances are you'll lose most of the florals as they move into those more clove-like flavors. Roasting into Full City while making sure that no second crack occurs can be good for espresso roasts, but again you're mostly going to get gingery spice if not a bit of well developed mandarin orange citrus.
The secret to bringing out the best of Ethiopian coffee is not just in roasting them lighter. The key really lies in the controlled velocity in 1st crack. The 1st crack in these coffees can start slow and then just keep trickling along without ever seeming to reach a defined conclusion. Allowing this to happen can result in some really muddled flavors in the cup or even just a lack of definition in the citrus notes and otherwise. While you don't want to dry out the coffee too quickly in the beginning stages, it's a good idea to make sure there's a little extra energy at least when you're going into first crack.
Giving the roast a boost right before getting into the crack and making sure that there's a nice rolling vigorous crack is what you're aiming for. Don't push right on through; once there's a nice rolling crack you'll want to pull back on that energy or adjust the air (depending on your roaster) in order to make sure you don't get too short of a crack. You're looking for somewhere in the neighborhood of a good minute and a half to 1:45, and you want a clear end point to the crack as well without too many straggler pops.