Many changes occur during bean development, and so do many mistakes. Bean development is the crucial phase where the flavors and aromas are created during roasting.
This article will explore what bean development is, how to address common mistakes made during this phase, and how understanding development time can improve or impact roasting skills.
What is Bean Development and What Changes Occur?
Paul Golding, head roaster at Paradox Roasters in Australia, emphasizes that bean development is a continuous process. He explains, “Technically, coffee beans develop from the moment they enter the drum until the moment they are ground and immersed in water for extraction.”
In the roasting process, beans undergo a series of stages that contribute to development. First, during the drying phase, beans lose moisture. Then comes the Maillard Reaction, a chemical reaction between amino acids and reducing sugars. Following the Maillard Reaction, a reaction known as Strecker Degradation takes place, where aldehydes and ketones are generated as amino acids react with carbonyl group molecules. This step is crucial for generating flavor and aroma. The breakdown of carbohydrates into simple sugars further fuels the caramelization stage.
Each chemical change and how it’s controlled will influence the flavor profile. The way and timing in which the beans are in the drum, undergoing specific reactions, will have an impact on the flavor. This should be considered an integral part of bean development.
Paul continues, “For roasters, however, the term ‘development’ refers to the progression of the bean’s roast state during the most dynamic stage of roasting for our senses.” While development refers to the structural and chemical changes that occur during and even after roasting, the term specifically refers to the final moments of roasting, when sensory changes continue to unfold.
The Development Stage
Roasters mark the beginning of the development stage when the first crack occurs. From this point on, the roasting pace and the degree of development will determine the coffee’s profile.
The initial chemical reactions lay the groundwork for the development stage. Olli Klitsch, founder of Flying Roasters in Berlin, explains, “Development determines the flavors we want to highlight, but it’s important to note that all roasting stages are crucial to achieving that.”
Olli refers to the Maillard Reaction, simply described as the reduction of sugars (fructose, sucrose, glucose) and amino acids, responsible for many of the aromas in roasted coffee. He adds, “After the first crack, chemical reactions (caramelization and the Maillard Reaction) bring out the aromas we’ve developed during the earlier roasting stages.”
Thus, the stages before the first crack are critical for the development and final outcome of the bean.
Olli also warns about the speed at which reactions occur after the first crack: “The beans dry out, and chemical reactions happen very quickly, so we stay focused on the development of the batch.” The development time after the first crack will be a key determinant in the overall flavor of the coffee. In the book *Home Coffee Roasting*, Kenneth Davis explains that removing the beans around the first crack will result in a cup that is “bright and sweet but also tea-like.”
Beyond this point, sweeter notes will develop due to further caramelization of sugars. However, the longer the development, the darker the sugars will become, causing a stronger bitterness from the burnt sugars. Coffee can develop an array of profiles depending on how it is roasted. Understanding the specific defects that can occur during roasting will help avoid undesirable effects on the flavor.
Problems in the Development Stage
Underdevelopment
Underdevelopment typically occurs when a bean hasn’t been roasted enough or is not fully roasted. Michael Macaskill, owner of Terbodore Coffee in South Africa, explains that “underdevelopment can result in grassy notes.”
Herbaceous and hay-like flavors in underdeveloped coffee can arise for several reasons. Paul explains there are two main scenarios that lead to underdeveloped coffee.
First, Paul states, “[This happens when] the coffee is ejected from the drum before the desirable attributes have had time to develop fully. Visually, the coffee will appear lighter than ideal, denser, and with higher moisture content.”
Second, underdevelopment can occur when “the coffee is not roasted evenly throughout the bean.” It may appear visually correct, but upon tasting, undesirable traits become evident,” Paul adds.
Extending the development time can help prevent underdeveloped batches. Ensuring a consistent application of heat to the beans is also crucial for even roasting.
Overdevelopment
Overdevelopment can also lead to undesirable flavors in the coffee. Paul notes, “Overdeveloped coffee may result in a loss of acidity, subtle floral notes, excessive caramelization, and the appearance of roasted flavors like burnt, charred, or bitter chocolate.”
However, Michael emphasizes that “there’s a narrow margin between a dark roast and overdevelopment.” Everyone’s palate is different, and a dark roast for one person might be overdeveloped for another.
Matt Perger, World Brewer Champion in 2012, says: “Development isn’t a scale like color, it’s a yes or no.” Conversely, coffee is underdeveloped until the sugars and acids in the bean have fully developed, and after that, it all depends on personal preference. Knowing the profile you want to achieve is all that matters. If the desired profile is dark with bitter notes, it won’t be a problem if that’s the intended result.
Baking
Baking coffee can fall into either underdevelopment or overdevelopment. The coffee may taste flat, even like bread or oats, if the roast has been baked. Paul explains: “Baking occurs when insufficient heat is applied at certain or all points of the roast, causing the coffee to progress too slowly.” This can happen before the first crack and the development phase, highlighting that flavor development in coffee occurs throughout the entire roasting process.
Development Time Rate: Using the Development Stage as a Tool
Roasters who use software can assess the degree of roast in terms of development time and the development time rate.
The development time rate is calculated after the first crack and expressed as a percentage of the total roasting time. This rate helps roasters understand the roasting time relative to their own roaster. Each roaster has different batch sizes, mechanisms, and thermal conditions, resulting in varying temperatures and readings. The development time rate allows for more precise comparisons between roasts and provides at least one indicator to achieve a more general consensus. This is useful for those who have roasted coffee to their liking and wish to replicate it.
For example, Paul explains that someone using software could “eject a [batch] roasted for [filter] coffee 40 seconds after the start of the first crack, which would correspond to a 6% development rate in a total roast time of 10 minutes and 30 seconds. If the result was satisfactory, they could reliably replicate it with the same coffee by always releasing it 40 seconds after the first crack, or at 6%.”
This precise information can be very helpful; however, Paul emphasizes, “It becomes a concern when you hear people say that 5% development is perfect, or 15% for espresso. That might be true sometimes, but we shouldn’t get stuck in absolutes [when it comes to coffee].” There should be caution when focusing too much on numbers.
Similarly, Olli reminds us that roasters should seek a more holistic approach and explains, “It’s practical to work with the development time rate, but even then, you can still end up with underdeveloped coffee. It’s also important to consider the charge temperature, when the inflection point occurs, the color, the final temperature, and other factors.”
In his blog, Scott Rao mentions that most of the exceptional coffees he’s tasted had a 20-25% development time rate. However, Rao advises roasters to fully understand the roast process, rather than focusing solely on the development time rate: “[This measurement] is not a guarantee of development; it’s simply one of many indicators of how the roast has progressed. It’s a practical rule and can be successfully broken, but like other rules, you probably shouldn’t break it before mastering it.”
Using data should be a helpful tool, but it shouldn’t be relied upon completely. Remember to consider your roast profile and use your senses to guide you. Learn how the first crack sounds, and from there, how each stage of development sounds. This will also provide guidance during the roast, trusting yourself, the roaster, and your knowledge of the coffee and the machine.
If you have access to this data, use it wisely. Always consider the entire roasting process and what has occurred during that time. Bean development is continuous throughout the process, and this will affect the final development time and proportion.
Understanding the development and the development stage is essential for the fundamentals of roasting: knowing what happens during development, what to avoid, and how to use data to expand your knowledge. Improving your roasting skills is all about practice. As Michael says, “There’s no substitute for experience… It’s a combination of coffee, the machine, and the roaster working together. And when these three components are in sync, you get what you’re looking for.”