“Is this coffee dark?”
“Is it strong?”
“Is it bitter?”
We get these questions all the time, and they’re great questions! The simple answer is that most of our coffees are roasted quite light. Our single origins are often true light roasts, and our signature 8-Track Blend pushes closer to a medium roast.
However, the process of coffee roasting is much more nuanced than that! A single batch of coffee goes through multiple different phases during a roast, and each phase is doing something different.
Let’s break down the whole process, from green coffee beans to a fresh bag of roasted coffee.
Green Coffee
Before coffee is roasted, it looks totally different! The beans are green, and they’re small and quite dense. They arrive from the producer in huge burlap sacks, which contain around 150lbs of coffee!
If you inhale these bags, the smell may surprise you. They smell vegetal and fresh, a little like leafy greens or green pepper. A natural process coffee can also have a sweet, syrupy smell. Coffee at this stage is so dense that it would break a typical coffee grinder. We have to take careful precautions to ensure that no unroasted beans make it in the final product!
We drop a fresh batch of green coffee into a coffee roaster, preheated to 450 degrees (F). It’s vitally important to batch consistency that the roaster has preheated for a long time. If it’s too cool, it’ll slow the whole roast down, and noticeably affect flavor characteristics. A properly preheated roaster will make your first roast of the day identical to your last.
Drying Phase
Once coffee is dropped in the roaster, the bean temperature rises dramatically. From room temperature to 200 degrees (F) in just a minute.
During this phase, there actually is not much flavor development happening. We call this the drying phase because the moisture is literally evaporating. Green coffee has a moisture content of about 11%, while fully roasted coffee only has around 2%.
Notably, the beans lose a lot of weight as this moisture evaporates. The final product actually loses about 15% of its total mass from start to finish.
This phase takes up about half the roast, until the bean temperature reaches about 320 degrees (F). Throughout, the coffee transforms from green to a nice yellow color. As soon as it turns yellow, you know you’ve reached the next phase.
Maillard Phase
As soon as the beans turn yellow, they’ve entered the “Maillard Phase.” Named for the “maillard reaction,” which is seen all over food science. In the maillard reaction, which actually references a host of different chemical reactions, where amino acids and sugars break down and combine under heat to make hundreds of complex new flavor compounds.
This doesn’t just happen in coffee. These reactions occur when you sear steak, toast bread, or roast grain for beer. It’s all over food science, and they are responsible for plenty of your favorite complex flavors.
It’s quite a sensory experience. When you monitor a roasting batch of coffee, the smell changes abruptly from vegetal greens to the smell of fresh bread or popcorn right as it turns yellow. Roasters often know they’ve reached this phase by the smell alone.
Towards the end of this phase, you also start to get some caramelization, where simple sugars break down into more bitter compounds.
When we want to improve highlight sweetness in a coffee’s flavor profile, we really slow the roast down around here.
In terms of time, this phase takes us almost to the end of the roast, until the bean temperature reaches about 400 degrees (F). However, the most critical phase in a roast comes at the very end.
First Crack
Right as the beans turn from yellow to brown, they explode to life.
We discussed the drying phase earlier, but up until this point, there is still some residual moisture safe inside the bean. Right around, 400 degrees (F), this last remaining moisture abruptly transforms into steam. The internal structure of the beans break at once, and they expand as steam releases out of their pores.
A bit like popping popcorn, this quickly goes from a few intermittent “cracks” to a cacophony of sound occurring all at once.
This is the point where you could end the batch. A coffee dropped right at first crack would be a super light roast. The moisture has evaporated and complex flavor compounds have been created. The question for the roaster now is how they want to shape the flavor.
Development Phase
The Development Phase represents everything after first crack. Its length is totally up to the roaster, they can end it any time they want, but it’s generally only the last 10%-20% of the batch. In a small batch, it's often under a minute long.
During this phase, we see even more caramelization take place, and the coffee moves from light, to medium, to dark roast very quickly. This is pretty intuitive when you think about it. The longer you let caramelization take place, the more bitter the final product will be.
The artistry here is about thinking through all the flavors you want to be in the final product. A very light roast will be acidic and bright; it could even still have some vegetal notes. A medium roast will be sweet and caramelly, and a dark roast will have a full body and a bitter flavor.
Of course, these are rules of thumb. The exact coffee you’re using, the process and region, all have much more drastic effects on flavor than the roast level. The goal of the coffee roaster is to accentuate what the coffee farmer has already produced in the bean.
As soon as the roaster deems the batch finished, they immediately drop the coffee in a cooling tray, halting all flavor development at once. Ideally, the beans should be cold to the touch within a minute of the end of the batch.
Conclusion
In summary, each phase contributes something different to the final product:
- Drying Phase: Moisture evaporates
- Maillard Phase: Complex flavor compounds emerge. Extending this phase controls sweetness.
- Development Phase: Post first crack. Extending this phase controls acidity and bitterness.
Some roasters push the coffee farther past this. You may have heard of second crack, which occurs long after first crack. This is where the carbon dioxide evaporates, and the brittle bean structure breaks down even more. If you’ve ever seen a super dark coffee with oily beans, that’s a coffee that went past second crack.
As many things go in coffee, this is an art as much as a science. We do test batches for every new coffee we try, and we taste test batches all the time for quality control. However, these phases are generally accepted rules of thumb for coffee roasters to live by.
So how do we roast our coffee? For many single origins, we aim for the Development Phase to last about 10% of the whole batch time, and we try to elongate the Maillard Phase to maximize body and sweetness.
For 8-Track Blend, we push the Development Phase time to around 15% of the roast. Just a bit darker for a richer final product.
Have more questions? Don’t hesitate to reach out and ask! Email me any time at nathanael@solidstatecoffee.com. We can offer brew tips, roast curves, or any specs about the coffee itself you’d want to know!
References
https://library.sweetmarias.com/first-crack-faq-what-is-first-crack-what-is-second-crack/
https://www.seriouseats.com/what-is-maillard-reaction-cooking-science
