Roasting Fundamentals

The Transformation

Green coffee beans are dense, grassy, and have almost no aroma. Roasting transforms them through a series of chemical reactions into the complex, aromatic product we recognize as coffee. In 10-15 minutes, a roaster applies heat to drive off moisture, trigger hundreds of chemical reactions, develop color, and lock in the flavors that the farmer, processor, and miller worked months to create. Done well, roasting reveals origin character. Done poorly, it erases it.

As a producer, I have a complicated relationship with roasting. I spend an entire year getting the cherry right -- selecting the variety, managing the soil, timing the harvest, controlling the fermentation, drying carefully -- and then a roaster has 12 minutes to either honor that work or destroy it. That is why I care deeply about how roasters approach our coffees, even though roasting is not my daily job.

The Roasting Timeline

Every roast follows a predictable sequence, though the timing and temperatures vary based on the roaster, batch size, and desired profile:

Drying Phase (0-5 minutes)

• Green beans enter the drum at 180-200 degrees Celsius (charge temperature)
• Moisture evaporates -- beans go from 10-12% moisture to below 5%
• Color shifts from green to pale yellow
• Grassy, hay-like aromas fill the roastery

Maillard Reaction Phase (5-9 minutes)

• The Maillard reaction -- a chemical reaction between amino acids and reducing sugars -- produces hundreds of aromatic compounds
• Beans turn from yellow to light brown
• Caramelization of sugars begins
• This phase builds the body, sweetness, and complexity of the final cup

First Crack (9-11 minutes)

• Internal pressure from steam and CO2 causes the bean structure to fracture audibly -- a popping sound similar to popcorn
• First crack is the defining moment: it marks the transition from endothermic (absorbing heat) to exothermic (releasing heat) reactions
• At first crack, the coffee is technically drinkable but still very light -- high acidity, bright, tea-like

Development Phase (post first crack)

• Development time -- the period between first crack and the end of the roast -- determines the balance between acidity and body
• Short development (15-20% of total roast time) preserves bright acidity and floral/fruity notes
• Longer development (25%+) increases body and sweetness but reduces origin clarity
• Second crack occurs if roasting continues -- the cellulose structure breaks down further, producing oils on the surface and darker, more bitter flavors

Roast Profiles for Different Origins

A skilled roaster adjusts the profile to match the coffee's character:

• High-altitude Colombian washed coffees (like our Castillo and Caturra lots) -- medium development to balance bright acidity with caramel sweetness. Too light and they taste sour; too dark and the origin character disappears
• Ethiopian naturals -- lighter roasts to preserve the delicate fruit and floral notes that make them distinctive
• Brazilian naturals -- slightly longer development to enhance the inherent chocolatey, nutty sweetness
• Anaerobic/exotic processes -- careful, often lighter roasting to avoid overwhelming the fermentation-derived aromatics with roast flavor

When we send roasters a sample of our anaerobic Bourbon, I always include a note about the fermentation protocol. A roaster who knows the coffee went through 96 hours of anaerobic fermentation with levadura inoculation will approach it differently than a standard washed lot. That context matters for building the right profile.

Sample Roasting vs. Production Roasting

There are two distinct roasting contexts:

Sample roasting follows a standardized SCA protocol -- small batches (100-150g), fixed time and temperature curves, designed to evaluate the green coffee's inherent quality without the roaster's interpretation. This is what happens before purchasing decisions. When I cup our lots before sending offer samples, we use a standardized sample roast so the green grading and cupping scores reflect the coffee, not the roaster.

Production roasting is where the roaster's craft comes in -- larger batches (5-70kg depending on the roaster), custom profiles developed through iterative cupping, optimized for a specific brewing method or customer preference.

The gap between a coffee's potential (revealed in sample roasting) and its expression (realized in production roasting) is where the roaster's skill lives. I have seen our lots score 86 on a sample roast and then taste even better -- more balanced, more nuanced -- in the hands of a great production roaster. I have also seen the opposite, where a careless dark roast turns an 86-point lot into something generic and bitter.

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Roasting is the bridge between origin and cup. Want to understand how different roast profiles affect the coffees from our farms? Join the community at skool.com/particular-3064 for roasting discussions and cupping comparisons across profiles.