The Stages Of Coffee Roasting: The first step in learning how to roast coffee is to recognize the progression and the different stages of coffee roasting. The technique itself – turning green coffee beans brown, is fairly simple.
However, perfecting the skill requires careful application of heat and close observation. So let’s see how it’s done and dive into the stages of coffee roasting!
Drying Phase
The drying is a critical initial phase of roasting. When coffees are processed and dried in origin, they don’t get completely dry. So, when roasters receive green coffee, there’s typically 10-12% moisture left in the bean to preserve its quality. Because of the moisture content, there needs to be a final drying phase that begins at roasting.
After heating the drum, in other words, setting a charge temperature, the beans are dropped from above into the drum, where the coffee immediately goes into drying.
Remember that timing and temperatures are usually based on the process, density, etc, of the coffees in play. The timeline of this phase is usually about 4-8 minutes and typically ends at around 160C. At this point, the beans move into the browning or Maillard stage.
Maillard Zone
The Maillard zone is the stage at which browning and colour change begin in the beans. During this stage, sugars and amino acids begin to break down, which also develops the acidity in your cup. Ideally, this phase isn’t rushed and is typically done with time to truly maximize flavour development from the chemical reactions.
Ideally, the roasting curve that is developed should take into consideration the timing of the Maillard phase.
By the end of the Maillard phase, the browning will have finished (moving from its green colour to a yellow colour and then to the brown colour), and the first crack will occur. This sign of development indicates that the bean has begun opening up and becoming less dense.
Development
During development, coffees begin to develop and open up by caramelizing and releasing sugars and different chemical compounds. At the first crack, we know that the bean has started development. We know this because the beans begin to crack like popcorn.
Ideally, we try to avoid a rolling crack when the beans break at different times and instead aim to obtain a roasting curve that allows all of the beans to crack at once. Usually, the first crack happens somewhere between 6-7 minutes.
Development times will vary depending on the roast level we aim for.
We typically end the development for light roasts right after the first crack. For medium roasts, our development time will be longer by a few minutes. We will typically hold the beans inside the drum right before or immediately after the second crack for espresso and dark roasts.
Cool Down
Cool down is essentially the final part before we let the coffee rest and go into packages. At this point, coffee is released from the roaster and into a circular area below the roaster over a fan.
This allows the coffee to cool and avoid any continued roasting. This also allows us to do a final step in the grading process where we remove any roasting defects such as Quakers (under roasted beans) or scorched beans (over roasted/burnt beans).
Roasting is a skill and an art that takes practice and experience. We are continuously learning and changing our approach as we obtain new coffees and look to develop the best-tasting coffees in the UK.