One of our friends recently roasted up some of our Ethiopia Guji natural process coffee. He had no idea what he was in for. He said he was “blown away” by the blueberry notes and if he hadn’t roasted and brewed it himself, would have thought he was drinking “flavored coffee.”
Of course we are proud of the quality beans we supplied him, but he clearly did a good job roasting or the promising “blueberry bomb” would have been muted or altogether lost.
Below is some background and thoughts to consider as you approach roasting natural process (or dry process) coffees. As always, we stand behind the position that technical understanding underpins roasting art. The more science we understand, the better artisans we become.
What is Natural or Dry Process Coffee?
For this article, I'll use Natural Process and Dry Process interchangeably. For a further breakdown, though, see Pupled Natural Process and Honey Process in the Glossary which are sort of hybrids between Washed and Dry Process coffees, but are still "natrural process" of sorts.
In any case, when I first began commercial roasting a couple decades ago, the Dry Processed (“DP”) coffees from Ethiopia could be pretty janky. They worked in blends, including espressos, but as single origin brews, they were rarely anything like clean and fruity. Longer roasts were necessary to develop the more chocolatey notes and make them more than just, "drinkable." While I enjoyed the uniqueness of the better lots, “dirty” and “gritty” were terms often scrawled across cupping note sheets.
DP coffees traditionally come from regions that have little to no access to sufficient water. If it’s hard to find water to drink, farmers aren’t going to use it to rinse fruit off coffee beans. Places like Ethiopia and parts of Brazil where water is scarce are among the most well-known producers of NP coffees. And processing naturals is tricky business.
After harvesting, the whole cherries are spread out on patios or raised beds for drying. The goal here is to gradually dry the fruit and inner seed (bean). Think about this. You have a patio covered with fresh fruit, laying out in the hot sun. For days. It doesn't take much to imagine the sound of insects buzzing around the fermenting fruit.
My family used to make wine and I vividly remember the smell of grapes fermenting in the pails almost immediately after picking them. It takes only a bit of juice bursting through the skin and encountering the yeast to start the whole organic process. When on their way to a wine press, it’s called “fermentation.” When sitting in a fruit bowl, it’s called “rotting.” You get the picture.
The painstaking work here, then, is to dry the beans gradually and evenly, keeping them mixed up to encourage airflow that helps prevent mold from developing. Raised drying beds encourage airflow from the bottom and are obviously superior to patios. But these more careful drying practices are reserved for those who are aiming for special quality. And quality comes from more than thoughtful drying.
Sorting the cherries is key as well. As we’ve noted in other posts, cherries ripen at different times on the same branch of a coffee plant. As you can imagine, different sugar and moisture levels among the varied fruit make uniform drying complicated. One option is selective harvesting, making several passes over the same plants over the course of ripening days. Sorting after harvest and drying on separate beds is another option. Whatever methods are used, sorting adds significant cost. And the only way to encourage farmers to take on this cost is to pay them for their work. Which we happily do, because we love top-lot NP Ethiopias!
In the end, when painstaking practices are followed in DP coffees and everything goes the way it is supposed to, there can emerge a wonderful lot of beans—widely varied in color, density, moisture, and sugar compounds—but rich in nuance and mystic character. It’s these coffees that evoke tropical fruits and dark berries. And it’s these coffees, with all their variables, that aren’t particularly easy to roast.
Making the Roast Count
This background above is designed to provide a framework for roasting. If you think about all the variation that exist in beans processed this way, you can imagine why it’s difficult to get a consistently roasted batch. Roasters often ask us why their batches look like they contain beans that are over roasted and others that are under roasted. I say, look at the variation in the unroasted coffee for your first clue.
This range of roast typically exhibits itself marvelously in the First Crack (“FC”). Some of the lower density beans will start cracking early on (it’s hard to hear some of the particularly light density beans going). Then, while the densest beans are just beginning to crack, the early poppers are deep into development. A conundrum indeed.
To control a profile, it’s helpful to envision getting a handle on a more uniform FC. If I am imagining some of the beans inside the roaster creeping toward FC while others still are lagging, I am looking for ways to get the beans to cooperate better. Try to moderate energy a bit with airflow and/or gas earlier in the roast to get all the beans more “thermally aligned” if that makes sense.
This means maybe soaking (click that term or see below) the beans a bit at the charge, or otherwise dragging out the drying phase some. Again, with different densities, beans are heating at different rates. By slowing things down a little on the front end, you can normalize the batch some as you creep toward FC. Then, just as you’re coaxing the beans to the starting line of FC, increase the energy to sort of shove all of them into a concentrated FC.
Be careful, because things can get a little tricky here as some beans are going to be releasing moisture at a more rapid rate, wicking energy away from the batch and threatening a rapid fall off in Rate-of-Rise (RoR), but some of the lighter density beans can also take off as they go exothermic and you’re back to having a widely varied batch. Measure your sessions as best you can and you should be able to get a feel for this pretty quickly. I find a little more airflow drives more heat into the beans, minimizing scorching and teasing out more sweetness.
Now, if you can get through FC somewhat rapidly/uniformly, it’s your call on how you want to develop things. If you’re aiming for tart, Starburst candy, you’ll want to drop the coffee maybe 15 seconds or so after FC. If you’re aiming for rich, syrupy fruit found in many good Ethiopia DPs, you can extend a little longer. But be careful: go too long after FC and you’ll see all those wonderful possibilities fade into a vapid disappointment.
It’s somewhat delicate work, but once you get the feel of cajoling the beans to dance together, you are on your way to creating some fantastic cups. Again, it’s always art form, but at least deeper understanding puts you in much better control of the canvas.
Soaking or Tempering –
This term has nothing to do with water! Soaking, tempering or reheating is a practice of dialing way back on the gas heat (or turning it off all together) for the first minute or two after charging, then cranking the heat to high and resuming your roast as usual. In line with the above discussion, this practice helps preheat and normalize the coffee temperature from the outer surface of the bean to its core. Without this heat “soak,” a preheated drum coupled with application of high heat at the beginning of a roast can overheat bean surface while the core is struggling to catch up. This preheating step is another way of getting all the beans (and all the bean mass) on the same page.