Roasting

From The Coffee Wiki

Roasting is the process by which processed green coffee beans are cooked and made suitable for brewing coffee. In this process, the coffee bean is heated in a coffee roaster for several minutes to bring the internal temperature of the bean up high enough to cause at least one small pop. Upon completing the roast process, the batch of coffee should be ready for grinding and brewing.

Contents 1 Roasting process 1.1 Cooling the beans 2 Chemical changes 3 See also 4 References

[edit] Roasting process

The process of roasting green coffee is fairly simple, requiring only that heat and constant movement be applied to the beans in some form of a coffee roaster. However, depending on the roaster used, there is a great degree of skill that goes into roasting suitable coffee.

When raw coffee beans are first exposed to heat in the roaster, the free moisture in the bean will begin to evaporate as the temperature of the bean rises. As the moisture locked within the bean starts to heat up, the bean begins to expand and eventually undergoes a small internal explosion known as the first crack. At this point pyrolysis begins, the sugars start to caramelize, and the bean begins to darken appreciably. It not until this stage of the roast that the beans can be removed from the heat and still result in decent coffee^[1].

During the pyrolysis stage, the bean begins to release oils which results in smoke emanating from the roaster. The internal temperature of the bean exceeds 350 degrees. If the roast continues past this point, the bean will darken further, and the internal temperature of the bean will continue to increase. Eventually the roast will continue to a louder second crack. The roast has now reached a darker state at which the beans become increasingly oily and the resulting smoke stronger and more abundant^[2].

[edit] Cooling the beans

Nearly as important as the roasting of the coffee beans is the cooling process. It is important that the coffee beans are roasted at a high temperature. Once they are finished roasting, the beans must be brought down to a much cooler (or just slightly warm) temperature as quickly as possible (within two to three minutes of the end of the roast) so that it does not continue to cook at merely high temperature. Some coffee roasting machines accomplish this cooling through a built in cooling fan, however other methods include the use of water to rapidly reduce the temperature of the beans. Cooling roasted coffee with water can be a quicker way of reducing the temperature of the beans so that it does not affect the roast. However, coffee which is quenched with more water than what can be evaporated by the heat of the beans will become stale more quickly than properly cooled beans^[3].

[edit] Chemical changes

While undergoing roasting, the coffee bean undergoes several chemical changes. The most obvious change at such a high temperature is the loss of water content. Water accounts for between 8 to 14 percent of the weight of unroasted coffee. After roasting, it will account for no more than 3 and as little as .5 percent of the bean's weight, depending on the degree of roast. The carbohydrate content of the coffee beans is also affected during the roast process, becoming caramelized. The resulting material is responsible for the darkened color of the coffee bean and the resulting cup of coffee. Further, the cooking of certain carbohydrates produces the oils responsible for the unique aroma and flavors of the brewed coffee^[4].

The total loss weight loss for an average roast is approximately 16 percent. As part of this loss, the coffee bean loses 9.7 percent of its original fat content and 21.1 percent of its caffeine^[5].

[edit] See also

• List of roasts

[edit] References