This section is all about the roast, I try to share some basic ground work and elaborate on things that influence the flavor in the bean.
Wet hulled coffees felt a little more forgiving when roasting, they took heat well and seemed to respond less aggressively when changing variables such as heat and air flow.
The washed coffee seemed to be influenced much more easily to variable adjustment and created larger swings in temps.
- Internal temp of roaster
- The temperature inside the roaster, often displayed through roasting software, used to dictate roast levels
- Bean temp
- Temperature of bean, when inside roasting machine, used to gauge level of roast
- Rate of rise temp
- The bean’s internal temperature that indicates how fast or how slow the bean is roasting
I anticipated a much faster roast at a higher charge temp, to bring out lighter notes in the coffee. I wanted to slow the rate of rise temperature to possibly lengthen the maillard phase and aimed for a relatively short development stage.
My goal was to bring the brighter notes out in the coffee that come from the washed process, when heat is applied up front. I also wanted to bring out the sweetness in the bean by lengthening the middle of the roast to increase caramelization. Then finish with a short development time to finish the roast at about 1 to 2 minutes after first crack.
- Charge temp
- The internal temperature of the roaster when the bean is dropped into the roaster
- Maillard reaction phase
- The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, induced by heat in the coffee roasting process. It results in the browning color of coffee as well as many volatile aromatics and flavors. It is not unique to coffee, and is at work in a variety of food conversion or cooking operations: toasted bread, malted barley, roasted or seared meat, dried or condensed milk.
- Development phase
- Development is the final phase of the roast, lasting from first crack to the end of the roasting cycle; the end temperature of the roast will depend on the desired roast degree. Development is generally accepted to be the phase of the roast most directly responsible for flavor modulation and development.
- First crack
- First crack in one of two distinct heat-induced pyrolytic reactions in coffee. It is distinguished by a cracking or popping sound in the coffee, and occurs between 390 and 410 degrees Fahrenheit in most coffee roasters. It has a sound more similar to the popping of popcorn, whereas the Second Crack that occurs around 440 to 450 Fahrenheit has a more shallow, rapid sound, like the snapping of Rice Krispies cereal in milk! First crack involves a rapid expansion of the coffee seed, and marks the point where water and carbon dioxide fracture, leading to the liberation of moisture from the coffee in the form of steam. First crack opens the crease in the bean enough to release remaining silverskin, or chaff. First crack is a clue to the roaster-operator about the roast level, and it's termination generally marks the first stage (City Roast) where coffee is acceptably dark enough to enjoy.
I anticipated being able to roast 6 test batches at 18oz each and roasting light, medium and dark for each bean.
What actually happened
I used a Mill City roaster to test roast because it allowed me to connect to Cropster, a roasting software that takes quantitative data in real time. This is a great tool to assist in finding a roast profile that works for coffee beans, then duplicating it.
The first change for me was the size of the roaster. I traditionally roast between 5 and 7 pound per roast, this time I was only roasting 1.125 pounds. The Mill City is a very detailed roaster that allows for multiple variable controls, this adds to the complexity of the roast.
In the beginning roasts I followed a specific protocol and adjusted the variables according to what I was achieving in my roasts. My first few roasts were charged at way too high of a temperature and though I didn't get any scorching on the beans, the turning point, color change and first crack times were all about 2 minutes shorter than they should have been.
- Scorching refers to a roast error that can be discerned by inspecting the roasted coffee, where darker burn marks appear in patches, especially on the flat surfaces. These can be seen as the coffee reaches 1st crack, but can sometimes be hidden by roast color at darker roast levels. But the flavor defect that results will remain. It can easily be tasted in the cup; burnt or smoke flavors, or a lack of sweetness. It is usually the result of an over-heated roast environment (initial drum temperature too high), or over-charged roast drum (too much coffee in the drum, or possibly not enough air movement. Scorching is also called Facing.
- Turning point
- The turning point is the first big change in your roast profile. It’s when the heat stops falling, and starts increasing instead. And although your roast may have only just started, when this happens you’ve already established how the entire roast will continue.
- Color Change
- Before roasting, coffee beans are blue-green. They change to brown because of the production of melanoidins. These are polymers that form when sugars and amino acids combine under heat. Chaff, or silverskin, will also come off during roasting. This is the papery outer layer of the coffee bean.
The first roast of Timor finished at about 5 min and I was aiming for a roast time of 6 to 8 minutes.
For the second roast of Timor I lowered the heat and left it alone. I felt it stalled towards the end of the roast. Though the lower temp allowed a longer maillard phase it could have used more. This was my favorite roast and most balanced
The third roast I adjusted the heat at turnaround and this ended up shortening the maillard phase. This cup was the second best tasting roast for Timor.
For Papua New Guinea's first roast, I adjusted the heat to medium and the fan to low for charge. At turnaround I increased the fan to medium and didn't touch the heat. I increased the fan speed to high at the first crack and finished the coffee just before the second crack. If you look closely (pic included below) you can see a sheen on the coffee, it's an oil layer that comes to the surface when you roast into the second crack as your bean temperature increases.
What I learned
Test or profile roasting is a process and doesn't always go according to plan. All data is informative at some level and gives indication of how the bean will react under heat. This information is instrumental to finding the best roast profile.
Overall the time spent roasting both Papua New Guinea and Timor was informative and allowed me to better understand how these washed coffees roast.
I look forward to sharing my notes and roasting curves on the first batch of this series.
Batch 1 Series 1 Roasting Notes
September 2nd, 2022
My first roast of the day:
Papua New Guinea (1st roast of day)
- For the most part the roast went amazingly well. I had a great turn around time, my rate of rise was on par and the temps were all progressing at the pace I anticipated. But the first roast of the day was not a solid representative of the remaining roasts.
- The roaster usually is inaccurate on the first roasts if it has not been warmed up properly. There are a few ways you can acclimate the roaster to be consistent and I try to follow those, but still usually have a small variant in roasting temps and curves
My second roast of the day:
Papua New Guinea (2nd roast of day)
- Though I followed a specific protocol to heat up the roaster it was still not consistent and seemed to run a little hotter and quicker than the first roast
- I heat the roaster well above charge temp and then let it cool to charge temp several times before my first roast
- The differences influenced the color change temp, first crack time and ending temp of roasts
- First roast, first crack was two minutes longer than the second roast
- Temperature of second roast crack, was 3 degrees hotter than the first roast
- The second roast bean temp was 8 degrees hotter when dropped out of the roaster
- Overall both roasts had similar development times and the variants were not large enough to create noticable changes in flavor
My third roast of the day:
Timor Leste (3rd roast of day)
- I knew that the roaster was warmed up at this point and I started to create more consistency in the roasts.
- My only issue with this roast is the drying phase, I am aiming to be closer to a 30% v. the 40% accomplished in this roast
- With a shorter “drying phase” I hope to bring out more of the brighter flavors in the coffee
- Overall the roast went according to plan, but little details can add up so I focus on duplicating roasts as closely as possible
- My mindset after the first roast was to leave the heat alone and to adjust the temperatures with airflow of the roaster
My fourth roast of the day:
Timor Leste (4th roast of day)
- This roast was very similar to the last roast and I was able to closely repeat most of the previous roasts key phases
- I achieved about 2% more time in the maillard phase
- Hopefully adding to the sweetness in the coffee
- This roast overall was 3 min longer, the additional seconds in each phase add up