In the coffee industry, roasting is undoubtedly the most attractive link. The green coffee beans have almost no flavor at all - there is even a rather unpleasant vegetable taste. However, the roasting process can reduce amounts of a chemical called chlorogenic acid, transforming green beans into the aromatic and fruity coffee we love.

What Is Coffee Roasting?

What makes coffee so varied and delectable isn't just the bean, it's the roast. Coffee roasting is the heat process of producing the characteristic flavor of coffee by causing the green coffee beans to change in taste. When heat is applied to raw beans, those beans produce and release oils, and their natural sugars caramelize, contributing to the bean's colors and flavors.

The History of Coffee Roasting

Many of us are familiar with the wonderful legend of how Kaldi, the goat herder, and his prancing goats discovered coffee around the 9th century. However, do you ever wonder how and when coffee roasting came about?

Coffee first came around about 1000 years ago, but it wasn't until the 1400s that coffee roasting technology really started to take off, beginning in the Middle East. The first methods weren't really that fancy and really just consisted of a large flat spoon that got placed into a fire, with a smaller stirring spoon to help evenly roast everything. The Ottoman Empire and European colonists then took the drink around the world.

The next significant development came in around 1650 when drums were created to house the coffee beans in Cairo. The coffee roasting drum was made of metal, most commonly tinned copper or cast iron, and was held over a brazier or open fire, reducing fumes by sustaining heat inside the drum and making it safer and more practical. Besides, it also featured hand cranks to move the beans around consistently.

In the 19th century, coffee roasting was no exception to industrialization - patents began flooding in for more commercial roasters, such as Richard Evans's first large-scale coffee roaster, James Carter's "Pull-Out" roaster, and so on. It should be noted that instead of wood or coal, natural gas became the roaster's preferred heat source at that time, for it could create a cleaner coffee flavor profile.

With the development of the Second Industrial Revolution, electricity grew more accessible at the turn of the 20th century. Electric motors could reduce the intensity of the labor, improve the accuracy of the roast as well as achieve greater security.

In today's computerized world, almost all roasters today roast with very high precision, and it is possible to customize your specific tastes, types of beans, or blends.

The Five Distinct Stages of Coffee Roasting

Stage 1 - Drying

The raw coffee bean starts off containing around 10 - 12 percent moisture, which is evenly distributed in the tight structure of the whole bean. After pouring the green coffee beans into the roaster, it takes some time for the coffee beans to absorb enough heat to evaporate the excess water, so a large amount of energy is required for this first part. In the first few minutes, the appearance and smell of the coffee beans don't change significantly.

Stage 2 - Browning

So the beans have dried out and they now begin to brown. The structure of the coffee beans at this stage is still very firm and has aromas similar to basmati rice and toast. The browning reactions going on inside the coffee bean cause it to expand and it begins to shed its thin papery skin (the chaff).

The first two stages are very important. For example, if the moisture of the green coffee beans is not properly removed, the subsequent roasting stage will not be able to achieve uniform roasting. Even if the coffee beans look okay on the outside, they may not be fully cooked on the inside, and the flavor after brewing is very unpleasant. There will be bitterness on the surface of the coffee beans, and the sharp sourness and grassy taste of the bean cores that have not fully developed.

Stage 3 - First Crack

When the browning reaction starts to accelerate, a large amount of gas (mostly carbon dioxide) and water vapor is produced in the coffee beans. Once the internal pressure increases too much, the coffee beans begin to burst, making a crisp sound, and at the same time, they expand nearly twice. From this time, the coffee flavor we are familiar with begins to develop, and the roaster can choose when to end roasting.

Stage 4 - Roast Development

The coffee bean becomes browner and the surface smoother at this stage. In fact, the flavor of the end result is mainly governed by how long the coffee bean is subjected to heat after the first crack stage. The longer the time, the less the acidity and sweetness as the sugars and acids are caramelized.

Stage 5 - Second Crack

At this stage, the coffee beans crack again - this time it's a quieter more crackly sound and signifies that the structure of the bean is beginning to break down. Once the coffee beans are roasted to the second crack, the oil inside is more likely to be brought to the surface of the beans, most of the sourness will fade and another new flavor will be produced, usually called "roast flavor". This flavor will not differ depending on the type of beans, because its origin is from the effect of charring or coking, rather than the inherent flavor components inside.