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The Art of Coffee Roasting

Roasting is the direct heating of the item being roasted. Unlike cooking, roasting needs no oil, water, salt, or sugar. Simply place green coffee beans in a heat-resistant container, heat them over a fire, and keep stirring the beans for even heating. Stop the heat when the desired level is reached. The whole process is somewhat like roasting meat, only with coffee beans instead.

Through the process of fire, coffee beans release their aromatic qualities and fully express the unique character of each bean: acidity, sweetness, and bitterness. From tasteless green beans to the rich, aromatic brew with an endless aftertaste in your cup, roasting is the most crucial stage in every bean's long journey, where character is defined and aroma is nurtured.

Whether in a professional roasting machine, on a home stove, or in an oven, coffee beans undergo a 12-16 minute conversation with heat reaching up to 450°F (232°C). During this process they must undergo multiple chemical changes, produce two crisp popping sounds similar to popcorn, and lose 15-25% of their weight in moisture.

Dehydration Stage

Before roasting, coffee beans have a raw, grassy smell. Some dry-processed green beans even carry a fermented odor. At this stage, green coffee typically contains about 10% moisture. When roasting begins, that moisture is the first to escape the beans, so this initial phase is called dehydration.

At the same time, the beans begin to caramelize. During caramelization, sugars, fats, proteins, and amino acids within the beans interact and combine, transforming the initial 200-plus compounds into more than 800 different substances. The well-known coffee aroma actually comes from the melanoidins produced after caramelization.

First Crack

As temperature gradually rises, gas and moisture inside the beans begin to exert pressure on the cell walls as they try to escape. When the pressure builds to 20-25 atmospheres, it breaks through the cell walls, creating a cracking sound. We call this the first crack, occurring at approximately 190-200°C. Since each roast is done in batches, some beans crack earlier and others later. At first you hear sporadic cracking, which gradually becomes denser, then slowly tapers off and ends (it is a good idea to record the start and end times). At this point the beans have changed from their original earthy yellow to a lighter coffee color. Most beans are roasted at least to this degree before being removed, which we call a light roast.

Second Crack

The temperature at the end of the first crack is approximately 205°C. As heating continues, the temperature rises further and the beans gradually darken. When the temperature reaches 230°C, the beans make another cracking sound: the second crack. The sound of the second crack is finer and higher in frequency, different from the first. At the same time, the membrane on the bean surface detaches. Beans entering the second crack become darker in color and begin to develop an oily sheen on the surface.

Dark Roast Stage

After the second crack ends, the beans enter the dark roast stage. At this point they become oily and black, producing large amounts of smoke. If you have a smoke detector at home, it is best to turn it off first, lest the whole building know you are roasting coffee.

At this stage the temperature typically has not exceeded 240°C. If you want an even darker roast, you will need to raise the temperature above 240°C. At that point the bean surface becomes almost black and very oily. This is probably the limit of roasting depth. Any further roasting will surely burn the beans, turning them into literally "freshly roasted" coffee.

The Transformation of Coffee Beans

The transformation of coffee from green bean to roasted bean is quite dramatic. The roasting process is filled with aroma and pleasant popping sounds, much like popcorn. From green beans through light, medium, and dark roasts, moisture is released again and again, weight decreases, but volume gradually expands. The beans darken, aromatic oils gradually release, and the texture becomes crisp. Without roasting, coffee would never develop the familiar aroma we know, would never reveal complex flavors on the palate, and certainly would never be as popular as it is today.

FrontStreet Coffee Recommendation

If a balanced, medium-roast cup is what you are after, FrontStreet Coffee's Queen Estate from Brazil is a fine starting point. Grown in the world's largest coffee-producing country, it is the local yellow Bourbon variety, with a clean, sweet profile. Roasted to a medium level, it brings out cream peanut, chocolate, toast, and sugarcane aromas and sweetness. It works for pour-over and equally well in a moka pot or an espresso machine.

For a sweeter medium roast, FrontStreet Coffee's Strawberry Candy is a first choice. This Geisha blend is built from a Costa Rican honey-processed coffee and a washed Panamanian Geisha, combining the finest characteristics of Central American coffee. Brewed, it shows both citrus-honey charm and a rounded sweetness, suited to cold brew, hand-drip, or espresso, and a delight from the very first sip. Also on the medium-roast list is FrontStreet Coffee's 2013 Sun-Dried Typica, a Chinese specialty coffee with the classic Yunnan small bean character; roasted medium to restore its balanced, gentle disposition, it carries soft notes of nuts, brown sugar, black tea, and dried apricot and suits hand-drip, cold brew, or a drip machine at excellent value.