There are many ways to create a complex coffee through the roasting process. In this article we’ll talk about two types of complexity; complex acidity and complex Maillard flavors; the yin and yang of coffee flavors; acidity being the lighter/brighter flavors and Maillard flavors being the darker/heavier flavors and in most cases, we develop one to the detriment of the other.
For the sake of this article, I’ll be talking about roasting a single origin coffee, not a blend (because blending is another way to add complexity).
One of things we need to know is what the coffee has to offer us in the flavor department and for that we do a sample roast and cup the coffee. This allows us to determine if its already a brighter, acidic coffee or if it’s predominately a heavier, darker flavored coffee. A good, generalized example would be a natural-processed African coffee versus a washed-processed Central American coffee. The African in this case will likely be brighter and lighter and the Central American will be darker and heavier. Knowing the individual coffee and what it has to offer allows us to manipulate the flavor precursors in the roasting profile to produce the desired flavors and complexity.
Coffee naturally has a lot of acids and a lot of precursors to produce even more acids during the roast. However, the acids present in the raw product as well as the acids we form during the roasting process are fragile and decompose at moderately high bean temps. At around 190°C we’re breaking down acids pretty aggressively.
Therefore if we want to have bright, acidic flavors in our coffee we will need to have a lighter roast because the darker we roast, the longer the acids are exposed to the high temps and the more they decompose into other components with different, darker, heavier flavors. This is the main reason why darker roasts are generally less acidic.
We know the flavors produced by the Maillard reaction are caramelly, nutty, malty, etc. We also know the Maillard reaction is responsible for generating a vast majority of the flavors we associate with coffee. Therefore, the longer and/or the deeper we allow the Maillard reaction to proceed, the more of this class of flavors we’ll produce and thus, the more complex our coffee will be. But at a price; we’ll lose clarity (the antithesis of complexity in our case) and we’ll continue to decompose acids and the complexity will be more complex in a single class of flavors; those produced by the Maillard reaction.
See also: The Maillard Reaction: A Practical Guide
The momentum of the roast (the rate of temperature change over time) is one determining factor for how uniformly cooked-through the bean is. For example, a hot and fast roast will produce a wide difference between how cooked the outside is versus the inside. We know this by measuring the color of the whole bean and then measuring the color of the ground bean. When there is a big difference between those two measurements, we know we have a big difference in how much we roasted the inside versus the outside.
In general; low and slow produces a smaller difference between ground and whole-bean color and hot and fast produces a larger difference between ground and whole-bean color.
Putting it all together
Roasting to a dark degree and/or to a uniform ground v. whole-bean color destroys the lighter/brighter flavors and spending more time in the sweet-spot for the Maillard reaction develops more of the heavier/darker flavors. If we want a lighter/brighter cup, we should ensure our roast is hot and fast so that we generate a larger difference between the ground and whole-bean colors and preserve more of the brighter flavors still present in the less-cooked center of the bean.
If we want a darker/heavier cup, we slow things down and spend more time in the Maillard’s sweet spot (~150°-190°C), letting it generate more caramelly, malty, nutty flavors as it does its thing. We can even venture into the deeper/darker side of roasting and go into and past second crack and generate more of those very heavy, dark, carbony, bitter flavors if we so chose.
- For a complex, light/bright coffee: roast hot and fast
- For a complex, dark/heavy coffee: roast slow and low
In my roasting classes for SCA certification I dive much deeper into these topics, specific acids, more details on the Maillard reaction, momentum, etc. If this article has piqued your interest but you want more details, consider joining one of my classes!
Continue Learning: Looking for more articles about roast science? Check out this page for more!