Importance of Roasting Uniformity in Agricultural Research

Coffee is a crop with its quality influenced by a complex interplay of genetic, environmental, and processing factors. In agricultural research, understanding how these variables affect coffee quality and chemical composition is crucial for breeding programs, improving cultivation practices, and enhancing post-harvest processing techniques. However, one often-overlooked factor in such studies is the uniformity of the roasting process. Roasting is a transformative step that dramatically impacts the sensory and chemical attributes of coffee, and inconsistencies in this stage can obscure the intrinsic qualities of the beans, leading to misleading research outcomes.


In particular, variations in bean density and size play a significant role in how coffee responds to roasting. Beans of different densities—often due to altitude, variety, or growing conditions—absorb and distribute heat at different rates. Similarly, bean size influences the surface area-to-volume ratio, affecting how quickly beans develop aromas and lose moisture during roasting. Without proper adjustments to the roasting profile, such as modifications to end temperature, development time, and initial heat application, researchers may introduce variability that stems not from the agricultural conditions being studied but from the roasting process itself.


This journal investigates the critical importance of achieving roast uniformity when conducting agricultural research on coffee. By examining the effects of bean density and size on roasting behavior, we explore how modifying roasting parameters can ensure consistent roast development across different coffee samples. This approach helps to isolate and accurately assess the impact of agricultural variables, enabling us to draw valid conclusions about the relationships between growing conditions and coffee quality.

The Role of Roasting Uniformity in Coffee Research

Roasting is a complex chemical process that involves the Maillard reaction, caramelization, and the breakdown of chlorogenic acids, all of which contribute to the coffee's sensory profile. In research settings, where the goal is to evaluate how environmental factors—such as altitude, soil type, or processing methods—affect coffee characteristics, controlling the roast process and being consistent is paramount. Roast profile standardization, including warm-up and in-between roast protocols, and uniform sample sizes, ensures that the differences observed in the final cup result from the agricultural factors under study rather than inconsistencies in roasting.


However, the one-size-fits-all approach to roasting can be problematic when dealing with coffee beans of varying densities and sizes. Higher-density beans, which are often produced in higher altitudes, tend to absorb heat more slowly, necessitating a longer or higher-temperature roast with a higher initial heat application to achieve full development. On the other hand, smaller beans roast more quickly due to their higher surface area-to-volume ratio and may become overdeveloped if subjected to the same roasting conditions as larger beans. Adjusting end temperature, initial heat application, and development time based on these factors is therefore critical to achieving uniform roast outcomes.

Initial Heat Applications

When roasting coffee beans, initial heat application plays a crucial role in setting up a balanced roast. This phase determines how heat penetrates the beans, affecting moisture loss, heat conduction, and the overall development of aromas. When beans vary in density and size, the rate at which they absorb and conduct heat changes, and the initial heat must be carefully adjusted to accommodate these differences.


Thermal conduction within coffee beans is highly dependent on the moisture content in the bean. Water is an excellent conductor of heat, and the presence of moisture allows heat to penetrate more uniformly through the bean. However, if the initial heat application is too high for the physical properties of the beans, it can cause significant issues in how the beans develop during roasting.


When the initial heat is too high, the outer surface of the beans heats up rapidly, leading to quick evaporation of moisture. This causes the outer layers to dry out prematurely, reducing the amount of water available to conduct heat further into the bean. As a result, the core of the bean receives less heat, leading to underdevelopment in the center, while the outer layers can become scorched or overdeveloped. The result is a bimodal roast, where the exterior is overdeveloped (often leading to bitter, burnt aromas), while the interior of the bean remains underdeveloped, leading to muted or raw aromas that lack complexity. This inconsistency compromises the quality and uniformity of the roast, which is particularly problematic in scientific research, where precise evaluation of flavor and chemistry is required. In contrast, when the initial heat application is too low, the result is a baked coffee, exhibiting undesirable baked and bready aromas.


High-density beans absorb heat more slowly due to their compact structure and higher moisture content. Applying a higher initial heat in a controlled manner is often necessary to help these beans absorb enough energy to maintain uniform internal heat conduction. Low-density beans, with their less compact structure, heat up faster and lose moisture more rapidly. They are more vulnerable to scorching if the initial heat application is too high, as their surface dries out very quickly, reducing the moisture that aids in heat conduction. A gentler initial heat helps ensure that low-density beans maintain their moisture longer, allowing heat to penetrate evenly and avoiding the rapid loss of moisture that leads to uneven development and surface burning


Bean size also affects the surface area-to-volume ratio, influencing how heat penetrates the bean and how moisture evaporates during the roast. Larger beans have a lower surface area-to-volume ratio, meaning they absorb heat more slowly because heat must travel further to reach the core. These beans need a more carefully managed initial heat application to again avoid surface drying that can prevent proper heat penetration. A more controlled, moderate initial heat allows heat to gradually penetrate to the center without over-roasting the outer layers. Smaller beans, with a higher surface area-to-volume ratio, heat up faster and lose moisture more rapidly. A lower initial heat application ensures a more gradual and even heat transfer, allowing moisture to evaporate slowly, which helps maintain even development throughout the bean.


By adjusting the initial heat based on the physical characteristics of the beans, roasters can ensure that moisture is lost gradually, and that heat penetrates evenly through the bean. This is particularly important in scientific research, where controlling these variables ensures that the observed differences in coffee quality are due to agricultural factors, not roasting inconsistencies.


Development Time & End Temperature

At the same roast progression speed, beans of smaller size and lower density will reach critical roasting phases faster than beans of higher density and larger size. This is the case as they more easily absorb heat and release moisture, and retained water in the beans works as a prohibitor of roasting processes. Therefore, adjusting the end temperature and development time is crucial to reach similar roast levels for beans of varying density and size.


To determine development time and end temperatures for individual lots, Agtron measurements are used. Agtron in coffee roasting refers to a widely used system for measuring and classifying the roast level of coffee beans based on their color, and has in recent studies been proven to be the strongest and most precise predictor of roasting degree. The system uses a specialised machine that measures the light reflectance of roasted coffee beans or ground coffee to determine how light or dark the roast is. The result is expressed as an Agtron number, which ranges from light roasts (higher numbers) to dark roasts (lower numbers). In research, the Agtron system helps in reaching similar roast levels across different beans for a stable basis of comparison.

To achieve this effectively, a live Agtron meter can be installed in the roasting machine to measure the surface color of the beans in real time. However, because roasting involves color development throughout the entire bean, this tool acts more like a guide, giving a rough idea of the roast level. For a more accurate assessment, using Agtron measurements on ground coffee provides a better picture of the overall roast level and reveals any differences between the surface and the center of the beans.


By building a catalog of roasting profiles over time that accounts for differences in bean size and density for even roast levels, through Agtron measurements, you gain the ability to conduct accurate sensory research on roasted coffee. This ensures consistency and reliability in evaluating sensory quality.





In conclusion, roasting uniformity is vital for isolating and evaluating the effects of farming practices, genetic varieties, and processing methods on coffee quality. Variations in bean density and size demand tailored roasting adjustments, including changes in initial heat application, roasting time, and end temperature. By carefully modifying these variables, researchers can ensure consistent roast development across different samples, enabling accurate assessments of the agricultural factors that influence coffee’s chemical composition and sensory characteristics.