Coffee Roasting – The Mixture of Art And Science


What is coffee roasting?

Coffee roasting is the process of transforming the green cherry bean into the coffee bean that we usually see and buy at the coffee shop.

The coffee bean was first roasted in the 15th century by using the thin metal pan in the Ottoman Empire and Greater Iran. At the time, the coffee bean only can be roasted in a small amount. Until the 19th century, the commercial roasting equipment was developed and used in roasting a large batch of coffee beans.

Not everyone can easily become a coffee roaster. It requires a lot of skills, techniques, and experiences which take years to learn and master it. A few seconds late or early can make a batch of high-quality beans become a poor batch of roasted coffee. Experienced roasters use their senses and collected data rather than rely on technology.

Why do we have to roast coffee?

The coffee bean is usually stored in the form of green bean for maintaining the coffee quality and easy to transport. In the climate-controlled environment, a green coffee bean can be stored up to 18 months. It is only be roasted in the destination country where the coffee will be served.

Before roasted, the green coffee bean is very bitter and acidic; thus, it is almost undrinkable. The chemical reactions during the roasting process change the taste of the coffee bean and bring out its unique flavor and aroma hidden inside the green bean.

What changes during the roasting process?

The roasting process changes the coffee bean dramatically, both physically and chemically.

After the green coffee beans are checked and weighted, then they will be transferred to the roasting machine. Inside the machine, the heat starts, and the beans keep rotating to prevent burning. The internal temperature of the beans will increase, which makes it lose moisture. As a result, the beans become dryer, lighter, but larger. A regular coffee bean will lose 12 – 20% in weight while being 50 to 100% larger after the roasting process.

In terms of chemical change, when the green beans are rapidly heated to high temperature, the Maillard Reaction occurs, and Melanoids are developed. This chemical reaction changes the color of the green bean into the brown coffee bean, as well as creates the complex flavors of coffee.

Different coffee roasting level  

Every roaster has its favorite coffee roasts, and they name it base on the degree of roast.

There are many methods to determine the degree of roast. But the most popular is by the color of the bean. Depend on the length of time and the temperature in the roasting process, the color of coffee beans will be different.

In general, all the traditional roasts fall into these four color categories: light, medium, medium-dark, and dark roast.

Light Roast

It is the minimum level of roasting. The coffee bean at this stage has light brown color and no oil on the surface. This roast level will highlight the origin characteristics of the bean as well as the complex acidity.

Common roasts within this category are:

  • Light City roast
  • Half City roast
  • Cinnamon roast
  • New England roast

Medium Roast

This category covers the most popular roasts in coffee roasting. Most of the coffee shops in the US are using this roast, thus it is also called American roast.

At this level, the coffee bean has a medium brown color and still has no oil on the surface. The sweetness is developed, the aroma and flavor are stronger than a light roast, and acidity becomes more balanced.

Common roasts within this category are:

  • City roast
  • American roast
  • Breakfast roast

Medium Dark Roast

The bean has a medium to moderate dark brown color. At this stage, the roast character is prominent, which makes the origin characteristics become eclipsed. Oil starts to appear on the surface.

In terms of flavor, it is bittersweet with a hint of caramel flavor, and acidity almost disappears.

Common roasts within this category are:

  • Full City roast
  • Vienna roast

Dark Roast

Dark roast is the last level acceptable for coffee roasting. At this stage, the bean start smelling pungent as all the sugar in the bean is almost burnt. The coffee bean will have a shiny black color with more oil on the surface.

The bitterness is prominent, and the natural aroma of the bean is mostly gone.

Common roasts within this category are:

  • French roast
  • Italian roast

Which roasts have more caffeine content? Light Roast vs. Dark Roast

When it comes the caffeine content, there are a lot of people who think dark roast has more caffeine in it since it tastes stronger. The truth is that the caffeine content in the coffee bean never changes during the roasting process. Therefore, by the bean, the light roast will have the same caffeine level as a dark roast.

However, the measurement method that you use when making coffee will make the caffeine content different between light roast and dark roast.

Since dark roast loses more water during the roasting process, thus it is much lighter than light roast.

Therefore, if you measure the coffee ground by weight, then 10 grams of the dark roast will have a higher volume than 10 grams of light roast. As a result, coffee made by using dark roast will have higher caffeine than made by a light roast in this case.

In contrast, if you measure the coffee by the scoop, the density of the coffee ground will be taken into calculation. Since light roast is denser than a dark roast, thus one scoop of the light roast will have higher caffeine than one scoop of dark roast. As a result, coffee made by using light roast will have higher caffeine than made by a dark roast in this case.

What are the best roasts?

There is no such thing called perfect roast; it is all about personal taste and preference. Specific roasts might be more suitable for certain types of coffee drinks. Therefore, when you buy a coffee bag from a supermarket or coffee shop, there is always a written note on the packaging about the “recommended brewing method.”

Some coffeeshop might serve only 1 type of roast for all coffee in there menu since they want to keep the signature taste.

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