What is the roast curve and what happens in each phase?

Many times I have been asked the question of what is a roast curve, and I still remember when Cristina Garcés my roasting teacher explained to me that the roast curve was the recipe for the transformation of green coffee bean to roasted, she always stressed that if you wrong in this curve you can lose the coffee farmer’s 3-year job hence the responsibility of doing the job well.

With 10 years of being roasting I have been able to learn to identify the variables that help me to perform a good roast curve and today I want to share the steps I always take before designing a roast curve and what happens in each phase.

1. Coffee beans: when roasting I always have a roasting order, I like to start with washed process coffees, going through coffees with prolonged fermentation, honey and lastly those of natural process.

2. Preheat your roaster: for the development of a good curve it is essential to allow the roaster to preheat well, so you have more ease of playing with low starting temperatures and airflow.

3. Espresso or filtering: when working with coffee it is very important to know about cupping and preparation; the roaster must understand the different extractions and thus seek to develop indicated profiles.

When I am clear about these steps, I begin to roast.

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1. Start: My intake temperature is always 160°C to 180°C (320°F – 365°F) depends a lot on which bean I am going to roast, in this phase of the beginning of the curve we take into account that the humidity of the bean is from 10% to 12 %, its color is green and it is minute 0.

2. Equilibrium point (Turning point): as the name says is when the temperature of the roaster and the bean are in equilibrium and give way to the first reactions, in these phases we can modulate the acidity of the coffees extending this stage, the humidity has dropped and On average it is 8%, since the bean is clearer and we go in the 2 to 3 minute on average this depends on what roaster you are using.

3. Maillard Reaction: here we begin to notice that the acids are synthesized and the sugars dissolve progressively, in this phase the coffee already has 6% humidity, it turns yellow and on average time It’s 6 to 7 minutes.

4. First crack: pyrolytic reactions are formed, it is defined as the synthesis of polysaccharides and acids, an increase of water-soluble substances. The coffee has enzymatic notes (floral, herbal, fruit). The sharp expansion gives rise to a characteristic sound. Already in this phase the coffee has lost almost all its moisture must be less than 1%, its color is already brown and we go in 8 to 9 minutes.

5. Final: the development of the final phase of the curve I try not to exceed 2 minutes that corresponds to 20% of all the roasting time, in this phase, I get carried away by color and fragrance of the bean and the end must be for 11 minutes.

These data are roasting in a 6-pound San Franciscan roaster in my favorite place to roast which is Bogotá at 2,600 meters above sea level.