The phrase “sight roasting” is often used to refer to the art of roasting coffee, typically in small batches, using ones senses, as opposed to employing computerized or otherwise automated processes that are often used in large batch roasting. Sight is just one of the senses used when roasting in this style. In all honesty, it should probably be referred to as “sight, smell and sound roasting.” So just what role do these senses, the three S’s of craft coffee, play in the roasting process?
When roasting coffee, the beans will go through a number of physical and chemical changes. Sight is used to evaluate and observe the physical changes taking place. Color changes from green to pale yellow, tan – ultimately brown (or shiny and black, if charcoal is the taste desired from the coffee) can be observed during the process. The appearance of the surface of the bean as well as the size or expansion of the bean while roasting are other visual characteristics used to track the progress of a batch.
While the beans are changing visually, they give off certain aromas that serve as clues to what stage of roasting the beans are in. This is where the sense of smell plays a key role in the process. Early in the roasting process, the beans will emit a grassy or leafy aroma, leading to smells of hay, grain, nuts, bread – ultimately transforming into the smell of coffee that we all know and love. Experienced roasters will know if a batch is exhibiting these aromas too soon or too late during the roast or if there are any aromas that are abnormal for a particular coffee, and will make adjustments to the profile as needed.
When it comes to sound, there are two important times in the roasting process (or just one if a coffee is roasted to a lighter degree) when the beans give audible clues as to what’s taking place in the roast development. One is the first crack, and in darker roasts, a second crack occurs. The beginning stage of a roast is when free moisture is driven out of the beans. As the moisture is heated and turned to steam, the beans will begin to expand. Roasters will hear the first crack when the pressure inside the bean increases. The beans simply crack open along the seam of the bean and go from an endothermic stage (absorbing heat) to an exothermic stage (giving off heat). At this point, the coffee could be finished, although it would be a very light roasted coffee. As the roasting continues further, the beans will go through a second crack, which is audibly different from the first— more of a ‘snap’ as opposed to a ‘pop.’ Beans that have a second crack are more of a “Full City” roast (medium-dark to dark) and are larger and darker than they were during first crack.
Sight, smell, and sound cannot individually be used to draw the optimal flavor out of any given coffee. However, used together and tracked alongside the time and temperature of a batch, these senses become indispensable tools in the quest for a perfect roast.