Roasting 101: Heat, pressure, time and care

Roasting coffee is more than just…well, roasting coffee.

It requires an appreciation and understanding of where the coffee came from (its origin), what it has gone through (the processing), and what it can and will become (its destiny).

Roasting coffee requires the fundamental appreciation for the variables that will turn a green, hard, grassy bean that smells like freshly cut grass and tastes like dirt and convert it into a tanned, caramelized, delicate bean that elicits positive feelings and emotions in its fragrance and taste.

There is unique potential hidden deep inside every one of us; the same can be said for every origin of green bean. There are intricacies and talents embedded in the green coffee that can only come out with careful and thoughtful development — in the form of heat, pressure, time and care.

Roasting requires heat. Heat transforms the coffee from the grassy, water-laden seed from the parent plant into the brown sweet bean that we use to extract the flavors that are locked inside. The heat will be applied by one source or machine, but the type of heat transferred to the coffee can be varied.

The utilization of direct BTUs (British Thermal Units) is made possible by a direct flame from the burner. The flame will heat the coffee as well as the surrounding metals to create an environment for the coffee to absorb the energy from the flame.

The direct heat is one source of heat transfer. The second source of heat transfer is through the contact made with the surrounding metals in the roasting chamber by the green coffee bean as it tumbles through the roasting process. The third source of heat transfer is through convective heat (hot air) brought through the roasting chamber by the roaster’s fan.

The amount of direct heat to convective heat is modified based on the amount of unbonded moisture in the bean and also based on the internal temperature of the coffee bean. As coffee roasts, it will lose unbonded moisture in the form of steam. As the coffee loses moisture it becomes more susceptible to burning, and the amount of convective air is increased to reduce the effects of direct flame to a drying bean.

The internal temperature will also change the amount of convective air due to the exothermic reaction that will occur in coffee at temperatures of 380-390 F and again at 420-430 F. At these two temperature ranges the bean will give off heat to the roasting chamber that will increase the pressure inside the roaster and in turn will cause the roaster to increase the convective air to reduce the surge of heat being produced.

The time frame dedicated to roasting process is the “heart beat” of the coffee. The development of this “heart beat” guarantees that the right amount of temperature is being applied to the coffee over a period of time to bring it to its fullest potential. Roasting coffee has to occur within a certain time frame that is specific to each coffee. There are processes that occur at the country of origin that give the coffee its appeal. These processes leave the coffee with a certain amount of residual water that affects the roast setup and time of each roast.

There are over 1,200 chemical components in coffee, and the chemical reactions that occur in the roasting process have to occur at a certain rate under a specific high temperature limit in order for the coffee to take on the true taste of coffee and not to have unwanted flavors enter into the profile.

To roast coffee properly, we have to be able to apply the heat to coffee in the right source format, at the right time with the proper pressure to bring the coffee back to life. In the green bean format, the coffee is dormant, waiting to be brought back to life. The roaster (both machine and man) breathe life back into the coffee and under the right conditions, it becomes the best possible coffee that it can.

At S&D, that’s what we do; we take time and care and pride in our roasting process. We have dedicated and talented men and women that understand these conditions and are passionate about treating each one as a unique roast.

And that is what our customers have come to appreciate and love about S&D coffee: great satisfying flavor that is done consistently time and time again with tremendous pride and care.

Post authored by Toby Foreman, previous S&D Coffee & Tea Sr. Coffee Buyer.