Radiation / Radiant Heat
Heat transfer in the roaster via electromagnetic waves. This source of heat transfer cannot be discounted; however, true radiation can only be measured consistently in a vacuum.
Rate of Rise / Rate of Change (RoR, RoC)
a measurement of the change in temperature over a given time period. E.g., the RoR at the beginning of Maillard Stage was 10F degrees every 30 seconds. Sometimes called “heat delta.”
Many roasters will suggest that you rest coffee a number of hours or days prior to first brewing. This allows the coffee to degas – releasing gases, especially carbon dioxide, that have built up in the bean as a result of roasting and can contribute to bitter and other undesirable flavors.
Roast Color / Roast Degree
The color of the finished roast. Although there have been many names given to different degrees of roast; light, medium, dark, city, french roast, etc., none actually describe a metric or objective measurement. Spectrophotometers or similar color reading devices can objectively measure reflectivity and may provide repeatability and consistency to achieve the same degree of color/roast for every batch.
The charted visualization of data from temperature probe(s) collected during the roast, plotted as time (y axis) over temperature (x axis), and a part of a complete roast profile. (See also: S Curve).
The difference between the weight of a batch of green coffee and the weight of the same batch once roasted (sometimes called “post-weight” and may be expressed as a percentage). This figure is important for multiple reasons, including roast data, but also inventory, forecasting and costing your product.
A roast profile can be thought of as a recipe. It is the purposefully created blueprint of the manipulation of the coffee roasting process, using the application of heat and airflow, to influence the temperature of a batch of coffee over the time of the roast. The roast profile may include (but is not limited to) its roast curve, rate of rise, roast stage times, temperatures, and roast stage percentages, end time, roast color, roast loss, etc.
Three convenient divisions of a roast into segments, referred to in this glossary as Drying Stage, Maillard Stage, and Development Stage, often divided into time ratio percentages.
The name given to the ‘normal’ roast curve produced by plotting the roast data of time (y axis) over temperature (x axis) on a graph. Left to its own devices coffee introduced into a hot drum/chamber will reduce the environmental temperature until the beans and drum/chamber air come to equilibrium. With enough energy input, the coffee, as an endotherm, will ascend in temperature until it exotherms at first crack, releasing energy and moisture. A roaster operator can influence this process and collate the data to create a roast profile.
a small batch, often around 100g, usually roasted to a specific roast profile which encourages minimal manipulation by the roaster (operator and machine). These roasts are usually lighter in color than a standard production roast and are roasted on a sample roaster. These roasts are typically created for the purpose of evaluating the quality of the green coffee. Sample roasts of different coffees are often cupped side-by-side. As such, among the more important qualities of good sample roasts is consistency, particularly of roast loss, roast color, and roast length.
caused either by excessive drum or environment temperatures (e.g., too hot of a charge temperature) and/or a slow drum speed, scorching is caused by conductive heat contact from the drum or bean-to-bean. This roast defect presents as dark, burnt patches on the front or curved surfaces of the bean. The result is an ashy, burnt, ‘roasty’ taste to the coffee even if it is not dark in overall roast color.
The second audible exothermic reaction the coffee beans undergo when roasting. A faster, shallower sound that first crack occurring at around 440 F, second crack is a further marker of pyrolysis and indicates an increased fracturing of the cellular matrix. Coffees taken to, through, and/or beyond second crack are typically considered “dark” in roast color.
Single Origin (S.O.)
This term can refer to coffee from one lot, farm, location, mill, or simply country depending on the person using it. It is the opposite of a blend (although, based on the loosely defined nature of S.O.s, one might create a “single origin blend” of coffees from the same farm or country, e.g.).
A roast color measuring instrument, often referred to in coffee roasting by a brand name, such as Agtron, ColorTrack, etc. This device differs from other spectrometers (such as mass spectrometers) as they only measure the intensity of electromagnetic radiation (light). By recording, in wavelengths, how much of the instrument’s light source reflects off of an object or is absorbed by it, it will give a reading, which can be translated to a roast color / degree.
Roasted coffee which has lost its freshness and flavor profile. Roasted coffee begins to stale the moment it exits the roaster. Coffee staling, as with all staling, is due to contact with oxygen and the process of oxidation. The more intense the exposure to oxygen, the faster your coffee will oxidize. There are many ways, via chemical intervention (e.g. nitrogen flushing), packaging and storage protocols (e.g., One-way valve bags), to help to slow this process down. However, you cannot fully arrest coffee staling.
a term used to describe a phenomenon when the batch of coffee being roasted resists heat absorption. The rate of temperature rise of the coffee will slow and may dip into negative temperature deltas over time. It may also, in the most extreme cases, slow to such a degree as to not achieve first crack. In other cases, it may achieve first crack, but the slower portion of the roast may contribute to lower acidity, hollow flavors and a less complex cup. These characteristics are summed up by the nomenclature baked coffee.
This chemical process is dependent on the Maillard reaction, and the availability of amino acids present in the green beans. The carbonyl-grouped molecules created as a result of the Maillard reaction interact with amino acids, contributing to melanoidin production (heterogeneous, nitrogen-containing brown polymers that absorb light). The melanoidin reaction complex is also responsible for the production of aromatic compounds such as aldehydes and ketones.
a tongue-in-cheek reference to coffee’s flash point, around 475F.
A roast defect where the narrow, fragile tips of the coffee beans are burnt by applying too much heat too quickly. These burns are caused by heat affecting the most fragile part of the bean, and may not be evident on other parts of the bean, or conversely, may be seen in conjunction with scorching or facing.