Understanding How to Roast Coffee: The Foundation of Great Flavor

The coffee cherry is a fruit from which the bean coffee originates. Coffee beans are the end result of this process. A green bean's aroma is beany and grassy before it's roasted. Contrary to popular belief, green coffee beans have no discernible aroma. Eight hundred to a thousand different aroma compounds are created during the coffee roasting process. This is what gives coffee its distinctive aroma and flavor. Roast profiling allows us to manipulate the levels of these aroma compounds in coffee, and thus the coffee's flavor.

Pre-roasting coffee green bean measurement

The Art of Roasting Coffee

Roasting is the process by which coffee beans go from their natural green to a darker brown. It can be prepared in a variety of ways, each of which contributes slightly different flavors. In this article, I'll cover the basics of roasting as well as commercial roasting. Tomi writes on his blog about the various home coffee roasting methods available.

Methods of Roasting

The roasting process consists of three distinct phases: the drying phase, the browning phase, and the development phase.

1. The Drying Process

The moisture content of a coffee bean is 8-12%. To begin roasting, we must first dry it. The drum roaster (typically used for drying) takes 4-8 minutes (for roaster designs, see below). At the end of the drying process, the temperature is typically 160 0C. Be especially cautious with drum roasters to avoid scorching the beans with excessive initial heat. Since the final phase of roasting is exothermic (heat producing), the drying stage is also crucial for preserving the bean's energy reserves.

Two, the browning process

When heated above 160 degrees Celsius, coffee takes on a toasted bread and hay aroma. At this point, the aromatic compounds are being formed from their precursors. The browning process occurs after the drying process but during the browning process drying still occurs.

Browning occurs because of the Maillard reaction, which begins at this stage. The Maillard reaction produces hundreds of different odor and color compounds called melanoids from the reaction of reducing sugars and amino acids. The roasting process slows down at this point naturally, and some roastmasters intentionally do so to promote flavor development. When the coffee has reached the final browning stage, it begins to pop. At this point, development can be considered to have begun, hence the term "first crack."

3. The cooking or maturation process

In the early stages of development, the reaction becomes exothermic, and the coffee begins to crack. The coffee's explosive flavor is the result of the bean storing energy while drying and browning. During development, the aromatic compounds of interest are forming. A coffee with a smoky flavor and an overly sharp taste is easy to achieve if the roasting process is not slowed down during the development phase.

Roasting and profile data can be monitored with Cropster.

Depending on the flavor profile and depth of roast, the development stage can last anywhere from 15 percent to 25 percent of the total roasting time.

To what extent do we roast

When judging the quality of a roast, the degree of roasting is a crucial indicator. Both a colorimeter and a taste test can be used to determine the correct amount. Most roasters aim to improve the coffee's natural flavors by adjusting the roasting process. Coffees that are dark roasted tend to be more bitter, while those that are light roasted tend to be more acidic. Also, light roasts are more likely to have fruity flavors, while dark roasts are more likely to have roasty, burnt flavors. The organic compound 5-hydroxymethylfurfural is abundant in lightly roasted coffee, giving it a fruitier flavor. Further roasting causes a breakdown of this compound into less fruity compounds. Roasty and burnt flavors are the result of an increase in sulfuric compounds. One general rule of thumb is that darker roasts mask the raw coffee's flavor more than lighter roasts. Light-roasted coffees are more easily distinguished from one another than their dark-roasted counterparts.  

Roast time

The roast degree of a coffee bean is the most influential factor in determining its final flavor, but the total roasting time and the duration of each roasting stage are also crucial. There will be more of the aromatic compounds you want if you roast quickly. Watch out that you don't scorch the beans! In comparison to coffee's overall flavor (which includes notes of fruit, berries, chocolate, and nuts), which is weaker Faster roasting also results in a greater production of aroma compounds during the early stages of development.

A quick roasting profile

You shouldn't always go for the fast roast. It could be because of the roaster's design (discussed further down) or the coffee itself. The coffee's full range of flavors is brought out by a quick roast. It is necessary to modify the roast profile if certain tastes are undesirable in the brewed coffee. Acidity, for instance, is a highly prized flavor, but low acidity is sometimes preferred on espresso blends. Coffee's acidity decreases as roasting time increases, because more of the organic acids can be degraded. It's times like these that a slow roasting oven can come in handy.

Plans for roasters

Multiple roaster models exist. Different machines can produce coffee with noticeably different flavors because of the way their designs influence the roasting thermodynamics. Drum roasters, where beans rotate in a drum that is heated from below by direct or indirect flame, are commonly used by smaller roasters. Because of this, the energy output of roasters is significantly increased. With these machines, roasting is very consistent, but the roastmaster needs to plan ahead by a few minutes. Because excessive heat at the start of the roast can burn the bean from the outside in, drum roasters are optimal for low and slow roasting. Paulig Kulma's Bertha roaster is a Probatone 5 drum roaster, which is the traditional method of coffee roasting.

While Mihkel listens to the first crack from our Bertha, he enjoys a cup of Paulig Kulma.

Fluidized bed roasters have been used for years in the industry. The fluidized bed roaster utilizes hot air as a secondary heat source. This allows for quicker roasting control. Roasting coffee beans in a fluidized bed allows for a more rapid process without sacrificing flavor or aroma. Our roaster at the Vuosaari roastery is a fluidized bed roaster. Some roasters, such as the Loring Roaster, combine fluidized bed technology with a drum, but the drum is heated indirectly by the hot air.

Roasting beans for use in a coffee maker's filter or espresso machine

Is there a significant distinction between filter coffee and espresso, or have you ever wondered what the difference is? Filter extraction is a gentle process that relies on gravity. Filter coffee can benefit from using highly aromatic, more acidic coffee. However, espresso requires a pressure of 9 bars to extract. What this means is that more flavor is being extracted into the cup. Coffee that was roasted specifically for espresso machines may not always taste as good when brewed with a coffee filter. Some roastmasters prefer to roast solely for the bean, regardless of the method of extraction, and thus strive for a coffee that is neither too light nor too dark.

Espresso coffee has traditionally been made from a dark-roasted, full-bodied, and low-acid variety of coffee. Even though roasting methods vary by country, filter coffee is typically lighter than espresso. Modern roasting techniques allow for a wider variety of styles. To give just one example, our Ethiopia Amaro Gayo espresso placed third at the Helsinki Coffee Festival. Lightly roasted with a fast profile, the espresso was extremely aromatic and had a low level of roastiness. The body was more luscious than hefty. Conversely, we'd like some of our coffees to have the same robust body as espressos. Then, to enhance flavor and lessen acidity, we roast and age for a longer period of time.

There is no end to the learning curve when it comes to roasting. One's knowledge of the bean is never-ending. Finding the optimal roast profile for the coffee's characteristics is the most exciting part of my job. I really hope this article was helpful to you and that you had a good time reading it.