Roasters mark the start of the development stage at the moment of the first crack. From here, the rate at which you’re roasting and how far into development will determine the profile of your coffee.

In terms of the roast process, coffee beans go through a number of stages that contribute to the development. First, beans lose their moisture through drying which is followed by the Maillard Reaction, a reaction between amino acids and reducing sugars occurs. Depending on Maillard Reaction, a reaction called Strecker Degradation takes place which involves the creation of aldehydes and ketones through amino acids reacting with carbonyl-grouped molecules, which is critical to flavour and aroma. The breakdown of carbohydrates into simple sugars then helps fuel the caramelization stage.

Each chemical change and how it’s managed will contribute to the flavor profile. How and for how long the beans are in going through particular reactions will affect the flavor, and it should, therefore, be considered as integral to the development of a bean.

We have asked a few coffee experts to highlight the common issues that can occur during bean development:


Underdevelopment generally occurs when a bean has not been roasted enough, or not roasted thoroughly. Michael Macaskill, owner at Terbodore Coffee in South Africa explains that “underdevelopment could lead to it tasting grassy.” The grassy and hay-like flavors of underdeveloped coffee can occur for a number of reasons. Paul explains how there are two scenarios that result in underdeveloped coffee.

First, Paul Golding, Head Roaster at Paradox Roasters in Australia explains that “the coffee has been released from the drum before the desirable attributes have properly developed. Visually the coffee will be lighter colored than it should be, denser, and higher in moisture.”

Secondly, underdevelopment can occur when “coffee is not roasted evenly through the bean.  Visually it looks correct, but upon cupping reveals some of the undesirable attributes” Paul says. Increasing the development time can help prevent an underdeveloped batch. Assuring a steady application of heat to the bean is also crucial to ensure that coffee roasts evenly.


Overdevelopment can also produce undesirable tastes in coffee. Paul says “Overdeveloped coffee can include loss of acidity and delicate florals, too much caramelization, also the onset of roasty flavors like charcoal, toast, and bitter chocolate.” However, Michael emphasizes that, “there is a small margin between a dark roast and overdevelopment.” Everybody has a different palate, and a dark roast for one person may be overdeveloped for someone else.

Matt Perger, World Brewers Champion 2012, says, “Development isn’t a scale like color, it’s a yes/no thing.” Instead, coffee is underdeveloped until the bean’s sugars and acids are developed, and after that, it is all down to personal preference. Knowing the profile you want to achieve is all you need. If the profile is dark and has bitter notes, this isn’t a problem if this is the desired outcome.


Baked coffee can also come into the question of underdevelopment or overdevelopment. Coffee can taste dull, even bready or oaty if a roast has been baked. Paul tells me, “Baking occurs when insufficient heat is applied at some or all points during the roast, so the coffee proceeds too slowly.” This, therefore, can take place prior to the first crack and the development phase. It refers to an earlier development in the bean, which highlights the fact that developing flavor in coffee is present throughout the entire roasting process.

Development Time Ratio as a Tool

Roasters with software can judge the roast degree in terms of development time and development time ratio. Development time ratio is calculated after the point of first crack, expressed as a percentage of the total roast time. The development time ratio helps roasters understand roast time in relation to their own roaster. Each roaster has different batch sizes, mechanisms, and temperature conditions which will result in different temperatures and readings. Development time ratios allow roasts to be compared more accurately and use at least one indicator for a more general consensus. This is helpful for those who have roasted coffee to their liking and wish to imitate it.

In his blog, Scott Rao mentions that most of the extraordinary coffees he’s tasted have had a 20–25% development time ratio. However, Rao continues to advise roasters to understand the entirety of a roast, rather than only focusing on development time ratio: “DTR is not a guarantee of development; it’s simply one of many indicators of how a roast progressed. It’s a handy rule of thumb and one that can be broken successfully, but like more rules, one probably shouldn’t break it before mastering it.”

Using data should be used to assist but not relied on. Remember to consider your roast profile and use your senses to help guide you. Learn what the sound of first crack sounds like, and from there, what each stage of development sounds like, too. This will also provide a form of guidance during roasting, relying on you, the roaster, and your knowledge of the coffee and the machine.

If you have access to this data, use it wisely. Remember to consider the whole roast and what has occurred during that time. Bean development is continuous throughout, and this will affect the final development time and ratio. An understanding of development and the development stage is essential to the basics of roasting: what happens in development, what to avoid, and how to use data to expand your knowledge.

If you improve your roasting skills, it’s all a matter of practice. As Michael advises, “There’s no substitute for experience… It’s a combination of coffee, machine and roaster working together. And when these three components are in sync, you get what you’re looking for.”


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