As the darkness of the days begins to consume the light, drawing nearer to the winter solstice, I am reminded of another ongoing conflict between light and dark – coffee. The debate about which shade of roast is superior has continued for decades if not centuries. So, I wanted to shed a little light on the subject (pun intended).
To have an opinion on roast degree, it is essential to understand what is causing the color change the roast brings and what that indicates in terms of flavor and quality. If you’ve been reading my column regularly, you likely know that coffee starts as a green bean or seed in its raw form. When these beans are placed in a hot rotating oven (coffee roaster), they undergo a series of chemical changes produced by applying heat over time. Most roasts last between 8-25 minutes. The first roast stage is meant to dehydrate the coffee, relieving it of water content. This stage is known as the drying stage, followed by the yellowing stage, where the coffee takes on a yellowish hue. During this stage, chemistry is in full swing as chlorogenic acids are converted into more complex acids that reveal themselves later as flavors on the bright side of the flavor spectrum. These flavors could include citrus, grape, apple, berries etc. As these chemical reactions happen, they begin to create energy and pressure of their own. As this pressure builds to a climax in the bean, it expands in size and alerts the roaster by making an audible sound known as “first crack”.
Starting with First Crack to the end of the roast is the most critical in determining the final flavor. You’ve just spent about eight minutes creating beautiful complex acids, and now it is time to decide how much of the acid you want to preserve and how much sweetness and body you want to create. This stage is known as the Maillard stage or sugar browning, named for Louis Camille Maillard. This French physician discovered the flavor effects of amino acids converting to sugars at high temperatures in 1912.
The sooner the roast is completed after first crack, the more acidic flavors including fruit and floral notes on the positive end and sour grass and garden peas on the less desirable side. As the coffee continues to cook, more acids are converted to sugars and then caramelized, producing sweetness and body in the coffee. In this stage, the roaster truly puts their stamp on the coffee by deciding the balance or imbalance they wish to produce. If you continue to roast for too long, the caramelized sugars will begin to burn by entering pyrolysis and creating more acrid and bitter flavors. When you go far enough, the coffee will make a second audible pop known as “second crack”. When you have reached this point, there are no more acids to taste or sugars to enjoy. You are left with the carbon coil and caffeine content alone. Caffeine on its own is the taste of pure bitter. This is why a genuinely over-roasted dark roast can only taste bitter. It is essentially caffeine and ash.
If you are roasting a truly quality green coffee, you should never roast to the level of a second crack. You would destroy all the quality and nuance the farmer has tried to create. You would only roast to such a degree if you are dealing with low-grade coffees with no subtlety or individuality to showcase.
This is the basis for understanding how flavor is achieved in coffee roasting and the choices the roaster must make. To find out more about how brewing different roast levels and other factors affect your enjoyment of these options, tune in next month as we complete the exploration between light and dark-roasted coffee and enter the new year with longer days growing.
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