Last week I talked about how we picked out a new coffee. We cupped a variety of Colombian coffees and chose the one that we liked the best - simple enough, right? Well now we start to get into the tricky bits - we just purchased an expensive and very large bag of this green coffee and now I have to figure out how to roast it to make it the best possible product to share with our customers. Preferably without wasting too much of it in test roasts.
How does a roaster go about doing that? Well, for me at least, it involves a lovely fusion of scientific theory and blind trial and error. Each new bean I deal with will behave differently, but there are general roasting theories and practices that usually carry through most coffees. This coffee we just got was well rounded and balanced with a very pleasant acidity when we cupped it at our supplier. It had great notes of green apple and juicy clementine with a dense sweetness like raw sugar to help give it a little bottom end to make it a very interesting cup while remaining accessible and easy to drink. Because it did not have any serious notes of heavy sugars or jammy fruits, I knew I would like to keep it a little bit on the lighter side and do what I could to accentuate the delicate fruit acidity. Still, I could push it a bit further than a coffee with fragile floral or herbal notes, so I could develop those sugars a bit to give the profile enough weight to keep the whole thing balanced. Overall, this would most likely not require an abstract or complicated roast, but I would need to make sure I payed close attention to it in the final stages to keep the temperature on target.
I haul the heavy bag into my warehouse and start warming up the roaster. I'll let it heat up for close to an hour - it's getting chilly and I want to make sure every part of the machine is at a consistent thermal capacity so I can replicate this roast in the future if it turns out the way I want it to. I weigh out my beans at a normal dose for the machine and I take it's moisture content. This information can be very useful as the releasing of moisture will effect how the temperature may fluctuate throughout the roast.
My beans are dosed, the roaster is hot, so I start a new program on my computer hooked up to the roaster that shows me a time over temperature graph. This will help me visually understand the roast development and control how the heat from the burners is being absorbed into the green beans. I load my beans into the hopper up top, start the program, and drop them into the machine. For the next ten and a half minutes, I watch the time over temperature curve tell me the way the beans are absorbing energy, and I tinker with gas control and airflow to keep control of the increase of heat. I keep decent control over the roast as it progresses, and when I drop the beans into the cooling tray I have finished a fairly simple, textbook roast - a good start to profiling a new coffee. I let it cool and I bag it, label and date it. It needs to rest now, freshly roasted coffee has a lot of gas inside that needs to dissipate before tasting begins, otherwise it may give off some uncharacteristic flavors.
The next day I open the bag and I grind up the new coffee, smell it, and pour hot water over it to begin a cupping of it. I let it brew and I taste it to evaluate what kind of roast I've given it. It's not bad, but it's not the same thing I tasted a few days ago when selecting it. The fruity notes have taken a bit of a back seat and the raw sugar notes are a bit too brown tasting - I've roasted it a bit too dark. I start the process over, but as I roast this batch I try to stretch it put a bit more in the second half to retain some acidity but keep the temperature a bit more mellow. I drop this batch a few degrees cooler than the previous one, and once again bag it and tag it. I taste it the next day and am welcomed with a spot on profile. I was fortunate that this coffee behaved fairly straightforward and only required two test roasts to nail down, it is not uncommon for a bean to take numerous educated test roasts to get down properly.
Satisfied, I saved the roast profile as is and began roasting for production, and I can't wait to see what the store staff and customers think about our new, special offering. If you're interested in trying a cup of the final product, pop into the shop for a pour over or fresh bag of the new Colombian Narino single origin, it's quickly becoming a personal favorite of mine.
Hayden Kaye is our Master Roaster and head of the Say Interesting Stuff department.