How to control variables affecting consistency in specialty coffee roasting

Ensuring that every roast is of good quality and consistency is one of the biggest challenges of coffee roasting. Because many factors can affect the roasting process, such as climatic conditions, the freshness of the coffee beans, or even unwanted errors by the roaster.

Uneven temperature

The biggest variable affecting batch consistency is the ability of each batch of coffee to maintain a constant temperature during roasting, says Morten, a coffee roasting expert in Denmark. Any variation in heat in the roaster can cause the ingredients in the beans to transform in different ways, resulting in uneven roasting. This can happen even though input parameters such as temperature, rotational speed, airflow, etc. are kept unchanged.”

Besides, the ability to transfer heat in and out of the coffee roaster will also affect the consistency, including the temperature of the air around the roaster. For example, a coffee roaster can reach the desired temperature in the summer more quickly than in the winter. Conversely, the roaster may need more time to preheat to the right temperature on cold days. For starters, not knowing the effects of ambient temperature can result in a day’s roast with inconsistent color, ripeness, and flavor. Morten also said that most roasters know that the day’s first batch is usually Roast. The main cause is that the coffee roaster has not been heated enough by preheating only. This is a common problem with most coffee roasters. So the roaster must understand how the roaster operates, the ambient temperature, and adjust the settings to achieve the desired color and Agtron rating.

Coffee lot size per roast

In addition to temperature, Morten notes that batch size affects roasting consistency. If the number of beans put into the roaster is different, but the roaster keeps the old settings, the beans will ripen unevenly due to the process, and the heat exposure time of each batch will be extra. Therefore, each different batch size needs to develop a new roast profile.

To do this, Morten recommends that roasters use an infrared (IR) temperature sensor to measure consistency when changing batch sizes. On the Stronghold S7X and other roasters with an IR temperature sensor, measurements of different-sized coffee batches are very accurate. These sensors only measure the surface temperature of the coffee beans without being affected by the surrounding temperature – something conventional temperature sensors cannot do. From there, the roaster can rely on the indicators to change the heating levels in the roast. However, this only applies when roasting the same coffee on the same machine.

Taste is the most important criterion for consistency, of which 80% is determined by the color of the coffee beans and the remaining 20% is determined by the roasting time. Therefore, roasters often focus on building and maintaining strict roasting records so that each batch of coffee is uniform. This is mostly based on the experience of the worker, so roasters often choose a roaster with good skills and the ability to concentrate during the roasting process to recognize the different stages of roasting, from the dry stage, first crack stage, second crack stage, until the end stage. They also invest in using coffee roasters that can precisely and consistently adjust the temperature and roasting time. With the supporting machine, the roaster can easily control the roasting temperature and time well to help the roasting level, color, and flavor of coffee beans be more stable.

Additionally, Morten said Coffee Mind and Stronghold did research and found that the roaster operating process is the deciding factor for consistency. Roasters can improve their texture by collecting and analyzing data after each process. Start by tracking basic metrics like roasting time, end temperature, and rate of change in grain weight; Note, record the variables on each roaster to find the cause of the inconsistency; Test, compare results with different roasters, roasting modes and analyze to discover influencing factors and establish the suitable profiles for your coffees. Based on the research, Morten recommends some guidelines on how to operate the roaster to achieve the best results such as:

– Keep equal distance between roasts (to ensure a stable temperature in the roasting chamber)

– Heating (increasing the temperature) before roasting larger batches of coffee or when the ambient temperature changes

– Quickly reheat the machine after finishing a batch

– Roast the first batch manually to minimize the effect of the cold roaster

As can be seen, the journey to make delicious, stable quality coffee specialties is not an easy thing. Besides strict standards in production and preliminary processing, the roasting stage also requires efforts from workers. If you want to experience specialty coffees with the original flavor, the same roasting configuration, come to XLIII Coffee!

Articles you may be interested in

– The first IWCA conference held in Africa marked a 20-year development journey

– Nyagishiru #1552 Coffee brings happiness to Burundi community

– How to sourcing sustainable coffee for the long term?