Sample coffee roasting: why it is needed and how it is carried out
What is sample roasting and why is it needed
Sample roasting is roasting a small amount of green coffee, usually from 50 to 300 g, on special compact roasters. In practice, samples of about 100 g are most often used. When loading above 300 g, roasting is already classified as industrial, even if a sample roaster is used for it.
A sample of 100 g is considered sufficient for a stable roasting process and capping in several cups
Depending on the stage of the coffee chain, sample roasting tasks may differ. On farms and exporters, it is needed for primary quality and uniformity checks, for importers — for selection and comparison of lots, for roasters — for making decisions on further profiling. At the same time, the general principle of sample roasting remains the same: prepare a sample of green coffee so that it can be correctly evaluated.
Sample roasting allows:
to identify taste defects that cannot be detected in green grain;
evaluate the purity of the cup and the uniformity of the batch;
compare several lots with each other;
understand the basic taste potential of coffee.
Sample roasting reduces the risk of purchasing low-quality grain. It is impractical to fry a large batch at once without a preliminary assessment, and small samples in an industrial roaster are very difficult to fry correctly.
The role of standardization and the SCA approach
There is no separate protocol in the industry that would regulate sample roasting as an independent process. However, the SCA fixes the requirements for the preparation of samples for capping in the Sample Preparation and Tasting Mechanics standard, which is used as the main regulatory document for the professional evaluation of coffee.
In a professional environment, sample roasting is not considered as a smaller version of the production
The standard does not specify a specific roasting profile, but it defines the parameters at which samples are considered comparable. For capping, a light or medium-light degree of roasting is recommended, given through the measured color, and not through verbal definitions.
The roasting level is not measured immediately, but after stabilization of the sample — in the range from 30 minutes to 4 hours after roasting. The measurement is performed on ground coffee prepared according to the capping protocol. The range of brightness L * is used as a reference point, which is approximately 26-29 in the CIELAB system, which corresponds to values of about 63-65 on the Agtron Gourmet scale.
The time frame between roasting and sample evaluation is also set. In SCA practice, it is customary to carry out capping no earlier than 8 hours after roasting and no later than 24 hours. This allows you to reduce the effect of active degassing and get a more stable result in the cup.
Dark roasting is not recommended, as it masks defects and smoothes differences between lots
SCA recommendations are not aimed at obtaining an expressive taste. Their task is to create a neutral reference point at which samples can be correctly evaluated and compared with each other.
Sample roasting equipment
In sample roasting, specialized roasters are used, designed for a small load and stable reproducible operation. The type of equipment affects the nature of heat transfer and which properties of the grain will be more noticeable in the cup. This is always taken into account when interpreting capping results.
Open drum sample roasters are considered a classic tool for roasting samples. Usually they are designed to load about 100 g of grain and work due to conduction — direct contact of coffee with a heated drum. Open drum sample roasters include, for example, models of the companies Probat, Joper.
Conduction roasting reveals coffee defects well
Open drum sample roasters of increased volume, 200-250 g, are a subtype of the same design, but solve a different problem. They are needed where it is required to brew many cups to evaluate one lot. Most often this is due to working with commercial varieties or batches of low uniformity. A typical example of such equipment is Burns sample roasters.
Closed drum sample roasters are similar in design to industrial ones, but smaller in size. They combine conduction and convection methods of heat transfer, and the roasting profile can be controlled more precisely. Such equipment is used for experiments and work with expensive lots. At the same time, some of the defects can be smoothed out, so the results of such sample roasting require careful interpretation. This type includes, for example, the Giesen WPG1 and Diedrich IR-1 models.
Convection sample roasters work almost entirely due to the flow of hot air and do not have a classic drum. They are designed for very small loads and are highly repeatable, however, due to the peculiarities of heat transfer, they can smooth out the manifestation of individual defects. Such roasters are often used for quick screening, working with microlots and during training. The most famous example is IKAWA roasters.
Laboratory automated sample roasters with mixed heat transfer occupy an intermediate position between drum and convection systems. In them, the grain receives heat from both hot air and heated surfaces. Such equipment is widely used in the laboratories of importers and roasters for serial work with samples. Roasters of Roest belong to this category.
On sample roasters from Roest, the process is fully automated and reproducible
There is no universal sample roaster in the industry that is suitable for all tasks. Any type of roasting imposes its own limitations and distortions. That is why when comparing samples, the key factor is not the roaster model, but the stability of the approach and understanding of the roasting process.
Sample roasting algorithm
Preparation
Sample roasting begins with fixing the conditions. They choose the standard load weight for a particular roaster in advance and try not to change it unnecessarily. The same applies to the start temperature and basic air and power settings. If conditions change from sample to sample, the results become disparate.
Grain is usually not sorted additionally before roasting. If the task is to evaluate the lot, the sample is fried in the form in which it will be put into operation. At the same time, a quick visual inspection is useful. It helps to notice obvious heterogeneity or extraneous inclusions.
Building a profile
The sample roasting profile is built simple and neutral — they do not select parameters for a specific lot or drink and do not seek to enhance individual taste characteristics. The task is to heat the grain evenly and bring it to the degree of roasting suitable for evaluation.
On average, sample roasting lasts from 8 to 12 minutes
At the start, avoid a sharp set of temperature. This reduces the risk of uneven heating and the appearance of shades of dampness. Next, they try to maintain a balance between the speed and duration of the process. Too fast roasting often emphasizes acidity to the detriment of sweetness, too stretched — smoothes the differences between the lots. The first crack is used as a reference point. Roasting is usually completed shortly after it begins, focusing on the color of the grain, smell and general dynamics, without developing the coffee much further.
Cooling
After the roasting is completed, it is important to cool the sample quickly in order to stop further thermal development. With a small volume of grain, a delay of even tens of seconds can noticeably affect the final result, therefore, active air cooling is usually used in sample roasting.
Fixing parameters
In parallel with roasting, the parameters are fixed, which are then used to interpret the capping results. In working practice, the weight of the sample, the total roasting time, the moment of the first crack, the basic conditions of the process and the visual assessment of the grain color are usually noted. These data do not replace tasting, but provide context for comparing samples with each other and allow, if necessary, to repeat roasting under the same conditions.
Sample roasting only makes sense if the same approach is applied to all samples
Evaluation of samples is carried out on capping after a rest period, usually during the first day after roasting. All samples are brewed under the same conditions: standard grinding, the same dosage, water temperature and brewing time.
The main thing
Sample roasting is a tool for preparing green coffee samples for evaluation. Its value lies in neutrality, reproducibility and the ability to compare samples under the same conditions. In compliance with the general framework and a stable approach, it provides a reliable basis for making decisions on the purchase and further work with coffee.
Sample roasting is always a simplified model. It does not show how the potential of coffee will be revealed, and does not replace work with production profiles. In addition, different types of roasters give different results when sample roasting. Therefore, the experience and stability of the approach here is more important than formally following individual figures.