Coffee Roasting Principles Detailed Guide to Specialty Coffee Bean Roasting Steps and Coffee Roaster Recommendations

Professional Coffee Knowledge Exchange For more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style)

Introduction

Following the previous lesson where we covered the "ingredients," this lesson will focus on learning the principles of coffee roasting and some coffee roasting terminology.

Coffee roasting is very similar to food cooking - it uses heat to make food more delicious, aromatic, and visually appealing. Our purpose in learning roasting is to find the most suitable roasting method for each coffee bean.

Understanding Roasting Machines

Roasting equipment comes in various forms - hand nets, iron pots, and even popcorn machines can be used to roast coffee beans. However, today we will focus on professional roasting machines, which are divided into direct-fire, semi-direct-fire (semi-hot-air), and hot-air types.

Direct-Fire Type

Uses flame to directly transfer heat to the coffee beans. The advantage is excellent expression of coffee flavor and aroma, but the disadvantage is difficulty in control, which can easily lead to scorched coffee beans and uneven roasting. This greatly tests the roaster's skill level.

Semi-Direct-Fire Type

Uses flame to heat a perforated drum, where the flame cannot directly contact the coffee beans, but instead heats them through the metal drum's heat and conduction air vents. The advantage lies in stability, and most coffee roasters use semi-direct-fire machines to produce roasted coffee beans.

Hot-Air Type

Uses a blower to draw in air, which then passes through a heating coil to increase its temperature, utilizing hot air as the heat source to roast coffee beans. The advantage is easy temperature control and less likelihood of scorching. The disadvantage is that flavor and aroma expression are weaker compared to the previous two types.

Key Terms to Understand in Roasting

There are often key milestones during the roasting process. Let's understand the names and meanings of these key points.

Dropping Point

This is the moment when green coffee beans enter the roasting drum, and it's also the starting point for calculating the roasting curve. Generally, the initial drum temperature is set relatively high, and it varies depending on the amount of green beans or their origin. The dropping temperature is typically controlled between 160-200°C.

Turning Point

After entering the drum, coffee beans rapidly absorb heat, causing the drum temperature to continuously decrease. When it drops to a certain temperature and stabilizes before starting to rise again, this turning point is called the "turning point."

Yellowing Point

At around 6 minutes, the green beans with high moisture content begin to turn yellow, and wrinkles slowly appear on the bean surface. This point is called the yellowing point.

First Crack

Commonly known as "first crack," before this occurs, coffee beans are in a state of heat absorption. When enough energy accumulates inside the beans and they expand, cracking occurs and heat is released. The beginning of first crack is generally determined by hearing 4-5 sporadic cracking sounds.

Second Crack

If we don't choose to discharge the beans but continue development, there will be a 1-2 minute quiet period after the first crack ends, followed by the second crack. The beginning of second crack is also determined by 4-5 cracking sounds. The second crack sounds are not as intense as the first crack but appear as deeper, lower-pitched sounds.

Between these milestones, there are also time periods with specific names.

Drying Phase

Refers to the period from dropping to the yellowing point. Although dehydration occurs throughout the entire roasting process, this period is when the most water evaporates from the green coffee beans. The length of the drying phase depends on the moisture content and hardness of the green coffee beans.

Intermediary Phase

Refers to the period from the yellowing point to the beginning of first crack. During this period, the coffee bean surface becomes light brown, begins to expand and release steam, emitting a toast-like aroma.

Development Phase

Refers to the period from the beginning of first crack to discharge. Only after first crack are coffee beans truly "cooked" in the physical sense, and the length of development time determines the flavor direction of the coffee beans. Simply put, insufficient development can result in under-roasted phenomena and lack of flavor. Short development time tends toward acidic notes, while long development time tends toward bitter notes. Over-extending development time may also flatten the coffee's flavor.

Due to different development levels of coffee beans, they exhibit different roast degrees. Based on the color value of coffee beans, they are divided into eight major roast levels.

Agtron #95: Light Roast

Discharge time: When first crack is about to end intensively

Agtron #85: Cinnamon Roast

Discharge time: Around the end of first crack

Agtron #75: Medium Roast

Discharge time: After first crack ends

Agtron #65: High Roast

Discharge time: During the quiet period between first and second crack

Agtron #55: City Roast

Discharge time: At the beginning of second crack

Agtron #45: Full City Roast

Discharge time: Before second crack becomes intensive

Agtron #35: French Roast

Discharge time: When second crack becomes intensive

Agtron #25: Italian Roast

Discharge time: When oil begins to seep onto the bean surface

What Can We Actually Control in Roasting?

Taking a semi-direct-fire roasting machine as an example, we can only control the dropping point (time, temperature), heat adjustment, damper control, and discharge time.

Heat adjustment is similar to using low or high heat in cooking. Increasing heat will accelerate temperature rise, while reducing heat will slow down temperature rise. Different periods during coffee roasting require different temperature rise rates, which requires us to adjust the heat accordingly.

The damper's function is to extract water vapor and silver skin from the drum, as well as assist heat adjustment in controlling temperature. At the beginning of first crack, more smoke is produced, so the damper should be opened wider to extract smoke, which avoids smoky flavors in the coffee. However, if heat is insufficient and the damper is opened too wide, it could lead to heat loss and diminish the coffee's flavor.

Learning coffee roasting is a long and challenging journey. Only by practicing with solid theoretical foundations will you not be caught unprepared. However, this process is often tedious and uninteresting!

For more specialty coffee beans, please add FrontStreet Coffee on private WeChat, ID: kaixinguoguo0925

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473