It may be a simple pleasure to coffee lovers, but behind every carefully crafted cup lies a precise science. As MENA’s specialty coffee scene expands, understanding the principles of roasting is becoming critical. Saeed AbdiNasab, coffee teacher and instructor, shares what every roaster needs to know, from heat transfer to energy delivery.

In some professional and educational circles, coffee roasting is still described through a vocabulary of “feel,” “instinct,” “good hands,” or accumulated experience. Such expressions are not entirely meaningless, since repetition does refine judgment. Yet scientifically, they are insufficient. They obscure the governing variable that structures roast outcome more decisively than any other: heat transfer. Roast quality is determined not by elapsed time alone, terminal color alone or even a single end-temperature reading. Instead, the determining factors are the mode, distribution, intensity and timing of energy delivery into the bean. Properly understood, roasting is not merely a craft act applied to agricultural matter. Rather, it is a thermophysical and thermochemical process in which sensory development emerges from the way energy is inscribed into structure.

A matrix, not a vessel

The green coffee bean is not a uniform object. It is a multiphase cellular matrix composed of free and bound water, polysaccharides, proteins, lipids, organic acids, minerals, volatile precursors and cell-wall structures of unequal density and resistance. When heat enters this matrix, it does not encounter an inert substrate. Instead, it encounters a body simultaneously undergoing enthalpic absorption, moisture migration, internal pressurization, structural softening and reaction-pathway activation. This is why superficial descriptions of roasting remain weak. Simply put, they describe appearance while leaving mechanism untouched. Significantly,
the roaster is never simply applying heat. Beyond this, they govern the rate at which energy traverses matter and thereby shape the transformation itself.

The three modes of roasting

Technically, the roasting process proceeds through three primary modes of heat transfer:

• Conduction: occurs through direct contact between the bean and heated surfaces, especially the drum wall
• Convection: transfers energy through moving hot air surrounding the bean mass
• Radiation: contributes energy from high-temperature surfaces and thermal fields.

The key question is not whether these mechanisms exist, but how they are proportioned and modulated within a system. Their balance depends, crucially, on machine design, drum metallurgy, burner configuration, airflow velocity, batch mass, drum speed and thermal inertia. Every roaster, therefore, constitutes a distinct thermal environment with its own pattern of energy distribution.

When conductive loading becomes excessive, this risks a separation between surface development and core development. Energy accumulates, furthermore, at the bean exterior faster than it can diffuse inward, producing steep thermal gradients. The result is developmental asymmetry in which outer layers may enter advanced thermal degradation. Meanwhile, the center remains comparatively underdeveloped. Defects like scorching and, in certain cases, tipping, are therefore not merely visual imperfections but indicators of energetic imbalance. By contrast, well-managed convective transfer distributes energy more evenly and reduces surface-core divergence. Additionally, it supports a more coherent development of the bean mass.

How time and color fall short

For this reason, roast time alone is analytically weak. Two batches may finish in 10 minutes. Yet one may reach that point through aggressive conductive loading while another progresses through a more balanced convective regime. Their temporal similarity reveals nothing about the thermodynamic pathway by which development occurred. Color, meanwhile, behaves similarly. It is a visible consequence of prior thermal history rather than a sufficient index of internal transformation. Indeed, coffees with similar color can differ substantially in porosity, retained gas pressure, volatile preservation, cellular fracture patterns and extraction behavior. Development, therefore, is best understood as the trajectory of energy migration through the bean over time rather than a simple timestamp.

The drying stage decoded

The early stage, commonly described as drying, illustrates how terminology can conceal mechanism. This phase is not simply the removal of water. More broadly, it involves thermal equilibration of the bean mass, redistribution of internal gradients, evaporation of free moisture and mobilization of bound water. It also includes the controlled weakening of cellular coherence. If the roaster imposes energy too aggressively at this stage, the bean surface may accelerate thermally while the center remains cooler. The result is embedded unevenness that later phases cannot correct. Alternatively, if energy input is insufficient, the bean enters later reaction zones without adequate preparation, leading to dull cup character and reduced aromatic clarity.

From first crack to development

In the mid-roast interval, the relationship between energy influx and reaction kinetics becomes decisive. Notably, Maillard reactions, sugar degradation, acid transformation and aroma precursor formation accelerate in response to temperature. Yet they depend not only on temperature itself, but on its relationship with time and moisture state. Excessive heat flux can push the bean exterior into advanced thermal states while the interior remains chemically behind. The resulting cup may present a paradox of strong roast notes combined with hidden underdevelopment.

The roaster should therefore not treat first crack merely as an acoustic marker. Instead, it represents a thermomechanical threshold where internal vapor pressure, gas generation and structural tension produce fracture and expansion. Its importance lies, specifically, in revealing how effectively energy has penetrated and reorganized the bean’s internal architecture. After this point, the roast enters a narrower operational corridor where further heat must balance aromatic development against the growing risk of pyrolytic domination.

Why thermal literacy matters in MENA

No rigorous account of the process can avoid heat-transfer kinetics. In particular, metrics such as “Rate of Rise” matter only when interpreted as indicators of the relationship between system energy and material response. Airflow, equally, regulates convective loading and smoke evacuation, influencing the chemical environment in which reactions proceed. Batch size, drum geometry, probe placement, burner responsiveness and exhaust design all participate in a single energetic system. The skilled roaster is therefore not merely someone who repeats timings. Beyond this, they understand how a machine stores, distributes and releases heat.

Here, philosophy reappears not as decoration but as method. Admittedly, many roasters imagine the bean as passive matter awaiting manipulation. In reality, the bean absorbs, delays, redirects and transforms energy according to its own structural conditions. The process becomes a dialogue between thermal intention and material response. A roast profile is therefore more than a technical record. It is additionally the trace of how energy encountered resistance and how that resistance yielded form.

This perspective, moreover, carries particular relevance in the MENA region. High ambient temperatures, variable storage conditions, logistical challenges and rapid market expansion place additional pressure on consistency. Under such circumstances, heat transfer becomes the hidden determinant of repeatability. Consequently, the distance between an occasionally successful roast and a consistently reproducible one often corresponds to the distance between intuition and thermal literacy.

Energy as interpretation

Roasting, I believe, should be interpreted not from the surface of the graph but from the material logic of how the bean receives and reorganizes energy. This is the argument I make in my book on the science and philosophy of coffee roasting. Indeed, quality is not produced by time alone, color alone or instrumentation alone. More than this, it is the organized consequence of how heat enters, moves through and transforms the bean. Ultimately, the future of roasting in MENA will belong to those who understand that coffee is not simply roasted. It is interpreted through energy.