What Roasting Science Reveals About the Coffee in Your Cup

What happens in the final minutes of a roast is not intuition dressed up as craft. It is applied thermal physics. The roaster leans closer to the drum, adjusting airflow by fractions, watching temperature curves climb on a screen, listening for the first crack - sharp, percussive, then another, then a cascade of them filling the roastery. The decisions made in those minutes determine whether the coffee you drink tomorrow tastes of stone fruit and honey or of ash and regret.

Most specialty coffee drinkers in Sofia - a city whose specialty coffee scene has grown to over sixty cafes and a growing number of independent roasteries - have walked past one of their windows, seen the tumbling drums, and moved on. The process looks simple: green beans go in, brown beans come out. But the September/October 2026 issue of Roast Magazine dedicates three features to unpacking what actually happens inside that drum.

Decaf Deserves Better Than Its Reputation

For years, decaffeinated coffee occupied the bottom shelf of specialty roasting. Roast Magazine's feature "Decaf Reconsidered: Insights for Better Roasting" challenges this directly. Decaf beans behave differently under heat. They are more porous, having already undergone a chemical extraction process, and they respond to thermal input in ways that demand adjusted profiles. A roaster who applies the same curve to decaf as to a washed Ethiopian will produce a flat, papery cup.

Roasting decaf well requires more skill, not less. When a roaster understands why decaf beans absorb heat faster and develop color earlier, they can coax out the same complexity that makes specialty coffee worth seeking out. The next time you see a roastery offering a single-origin decaf, ask how they roast it. The answer will tell you a great deal about their approach to craft.

Thermal Stress and the Chemistry of Flavor

The second feature addresses a technical challenge most consumers never consider: PAH4 formation. PAH4 refers to polycyclic aromatic hydrocarbons, compounds that can form when organic matter is exposed to high heat. In coffee roasting, managing time and temperature is not only about flavor development. It is also about food safety.

Convective roasting, where hot air rather than direct drum contact transfers heat to the beans, offers roasters more control over thermal stress. But control is not simplicity. The roaster must balance heat transfer rate against scorching risk, Maillard reaction development against unwanted byproducts. The roaster is not following a recipe, but solving a problem in real time. At Aroma Coffee in Sofia, owner Georgi Gagov holds an SCA Roastery Diploma, works directly with green beans, and adjusts temperature curves to manage precisely that stress.

Origin Sourcing: Value Beyond the Price Tag

Price is the easiest metric, but also the least informative. A high price paid to an exporter does not guarantee farmers receive a fair share.

What matters is the relationship. Roasters who visit farms, understand growing and processing conditions, and commit to multi-year purchasing agreements are building something that cannot be captured in a single transaction. When a roaster knows the farmer's name, the plot's altitude, the processing method, they are participating in a chain of decisions that ripples back to the origin. Transparency in sourcing is not about telling a nice story. It is about honoring the full chain from seed to cup.

What You Can Do With This Knowledge

So ask. Buy a bag of specialty coffee in Sofia and ask your roaster a few questions. How do they approach decaf? What do they know about thermal stress? Where did this coffee come from, and what is their relationship with the producer? These are invitations to a conversation the best roasters are already eager to have.