Roasters may get significant insight into how the roasting process works by keeping note of the factors that affect the final product of the coffee roast. Because heat plays such an essential role in roasting, temperature is a key variable that should be monitored. The creation of a roast curve that keeps track of these temperatures may assist roasters in improving their ability to forecast the outcome of a roast or make adjustments to their roast temperatures for improved outcomes.
Cropster, a company that makes software for coffee roasting, and Balzac Brothers, an importer of green coffee, have just just established a competition called RoastID – See the Curve, Match the Curve to test the expertise of roasters all around the globe. This online competition included of three rounds, and in each round, contestants had to evaluate five different roast curves in order to go on to the next level. In order to forecast how the temperatures shown in each curve will affect the coffee’s score and its attributes, the participants were required to match each roast curve to its matching cupping score.
The competition was complemented by informative webinars and question and answer sessions hosted by a variety of industry professionals, who discussed the effects that each curve would have on the roast that it portrayed. Here is what these professionals had to say, along with an explanation of how following certain curves affects the coffee that is being roasted.
What Are Roast Curves & Why do They Matter?
Roast curves are useful tools for monitoring roasts because they trace the heat in a roast drum at critical periods during the process of roasting. By illustrating how applying the same amount of heat to a batch at the same time may generate consistent outcomes, they can assist roasters in developing a guideline for duplicating a roast profile.
The stages that coffee goes through when being roasted, including as the drying, Maillard, and development phases, may be identified with the use of roast curves, which can also chart their progression. The duration of each process may have an effect on the flavour of the coffee. For instance, the length of time that the bean spends in the drying phase will have an effect on its acidity and body, while the length of time that the bean spends in the Maillard phase will have an effect on its sweetness and caramelization. Roast curves also check to see whether the appropriate amount of heat is supplied during each step of the roast.
The formation of a reference curve often involves the use of a roast curve. By using this reference as a guide, roasters may more easily duplicate a desired roasting profile. This is accomplished by comparing the temperatures and timings of a current roast to the temperatures and periods listed in the reference. Because Kenyan coffee beans are often rather thick, a reference curve for roasting Kenyan coffee could incorporate a higher charge temperature. Alternately, a reference curve for a coffee from Brazil with low acidity can contain a Maillard phase that lasts for a longer period of time. This would cause the coffee to have more sweetness and body.
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How Coffee Processing Methods Impact a Roast
Joe Marrocco, a management executive with List + Beisler, noted during round three of the RoastID competition that the manner in which the coffee was processed would have an effect on a roast curve.
He claims that since natural coffees are dried with their cherries still attached, the beans spend more time in an atmosphere that is dark and wet, which encourages fermentation and the breakdown of the beans before the roasting process starts. As a consequence of this, the beans will need a low and gradual roasting process in order to maintain their natural sweetness. In order to maintain the natural acidity of washed coffee, the roasting process would have to be sped up.
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A table that was used in the RoastID competition to list many aspects of green coffee that should be taken into consideration when determining how to roast a coffee and what the final cup quality would be.
Choosing the Correct Charge Temperature
When using a roast curve, it is important to maintain the charge temperature that is specified. This temperature reflects how much energy is present in the drum at the beginning of the roasting process. If you start your roast at a charge temperature that is lower or higher than what is shown on your curve, you run the danger of beginning your roast erroneously or losing control of the roast later on.
Anne Cooper, a Roasting Consultant with Equilibrium Master Roasters, emphasised in the first webinar that beginning with a charge temperature that is too low might put you behind the roast curve. This may require you to rush through the Maillard phase in order to catch up with the curve, which may result in a roast that is not fully developed. When the roasting curve for an underdeveloped coffee came in the competition, the taste notes suggested that coffee roasted in this manner would produce notes similar to grass or hay. This was evidenced by the fact that the coffee had an undeveloped flavour.
Anne also said that even if you begin roasting at a temperature that is too high, it is probable that you will still be able to follow your roast curve. However, throughout the process, you run the risk of producing an excessive amount of heat in the drum, which can cause your beans to burn and will result in flavours that are charred, smoky, and spicy.
A roast curve that was used during the RoastID competition that indicated that the roast was not fully matured. The beginning temperature of the roast was far lower than it should have been, which is what caused it to lag behind the reference curve.
Managing The Maillard Phase
The Maillard phase of a roast occurs when the heat from the roast produces a reaction between the amino acids and the carbohydrates found in the bean. Melanoidin molecules are produced as a result of this process, which browns the beans and creates flavour as well as body. The length of the Maillard phase that is indicated in a roast curve should be adhered to as a best practise in order to create the cup profile that is desired.
According to Rob Hoos, CEO of Hoos Coffee Consulting, speeding through or overextending your roast’s Maillard phase might have a detrimental influence on the cup character of the coffee. Extending the phase for an excessive amount of time might produce taste qualities that are too savoury, which may not be the intended outcome.
A table that compares the amount of time spent and the temperatures reached throughout the various stages of each of the five distinct roast curves. During the course of the competition, the alterations that were discovered in each curve are indicated by the notes that are located above.
Handling First Crack, Development Time & Turning Points
Following the Maillard phase comes the first fracture in the product. This explains what takes place when the heat and pressure cause the coffee beans to expand and break open, so releasing the steam and carbon dioxide that were previously trapped inside of them. When compared to the reference curve, a roast curve that hits first crack rapidly and then is dropped out shortly afterwards may provide flavours that are light, bright, and vegetal in nature.
The period that begins just after the “first crack” sound and continues until the completion of the roast is referred to as the “development phase.” When compared to a roast curve with a shorter development time, a longer development time often results in a shorter Maillard phase, which gives the impression of increased acidity and sweetness.
The amount of time that passes between the initial crack of the bean and the development period of the roast has a discernible impact on the bean’s degree of caramelization, as well as the acidity, sweetness, and overall tastes produced by the roast. When the time is shorter, the tastes may be brighter and less caramelised, and when the time is greater, the flavours may be more “developed,” or browned, caramelised, and less brilliant.
Anne and Shelby Williamson spoke about one potential problem that may arise during this period, and that problem is called stalling. Shelby is the current holder of the title of US Roast Champion and is Huckleberry Roasters’ chief roaster. This takes occur when there is an insufficient amount of heat delivered, causing the bean rate of rise to fall too rapidly or fall below zero. This occurs most often near the conclusion of the roast, when the amount of heat that is being applied is typically at its lowest.
A roast curve that was used during the RoastID Competition, showing that the beans were not sufficiently roasted. This kind of roast curve is distinguished by a lower end temperature as well as heat loss that occurs while the bean is in the process of developing (compared to the reference).
Every roaster has to create their own roast curves and adjust them based on the equipment they use, the green coffees they use, and the desired amount of roasting and taste profile of their clients. By adhering to a tailored curve, these roasters will be able to keep up their production of roasted coffee of a constant quality and prevent themselves from making expensive mistakes.