Coffee process of roasting

Green beans smell green earthy, so they must be heat treated in a process called roasting to bring about their truly delightful aroma.

Coffee beans are usually roasted in large batch dryers which spin and heat them evenly at temperatures that reach 550° F. In the USA continuous roasting of beans is the common method, using fluidization of beans in a perforated cylinder with a horizontal airstream.

The process consists of roughly three stages lasting about six minutes altogether: begin roasting, end roasting, quenching. During roasting heat is transferred by contact of the beans with the walls of the roasting apparatus or by hot air or combusted gases.

The bean is warmed intensely to drive off free and bound moisture which constitute about 12% of initial weight. During the roasting process, about 20 percent of the water content of the green beans evaporates and carbon dioxide escaped. They are accompanied by some carbon monoxide and organic volatiles.

The bean’s starch content is converted to sugar. The volatiles oils and acids that gave coffee its tempting aroma and delicious flavor are developed during the roasting process.

The roasting process is terminated at the desired flavor, indicated by the darkness of color.

When the desired degree of roast is reached, the beans have to be cooled down rapidly by water quenching or cold air in order to stop further changes in color, flavor and volume. Normally the product is discharged into an air cooler for rapid cooling to 104° F.
Coffee process of roasting