Coffee roasting is the process of applying heat to green coffee beans to transform their physical and chemical properties and develop their flavor, aroma and color. Roasting is a complex and dynamic process that involves many variables, such as temperature, time, airflow, humidity, bean size, bean density, bean moisture, bean origin and roaster type. Roasting can be divided into three main stages: drying, browning and development.
- Drying stage: This stage begins when the green beans are loaded into the roaster and ends when the beans lose most of their moisture and reach a temperature of about 150°C. The drying stage can last from 4 to 8 minutes, depending on the roasting method and the desired roast level. The main goal of this stage is to remove the water from the beans and prepare them for the chemical reactions that will occur in the next stages. The drying stage is important for preserving the acidity and sweetness of the coffee.
- Browning stage: This stage begins when the beans reach a temperature of about 150°C and ends when the beans reach a temperature of about 200°C. The browning stage can last from 2 to 4 minutes, depending on the roasting method and the desired roast level. The main goal of this stage is to initiate the Maillard reaction, which is a chemical reaction between amino acids and sugars that produces brown pigments and complex flavor compounds. The browning stage is important for developing the body and aroma of the coffee.
- Development stage: This stage begins when the beans reach a temperature of about 200°C and ends when the beans are ejected from the roaster. The development stage can last from 1 to 3 minutes, depending on the roasting method and the desired roast level. The main goal of this stage is to complete the Maillard reaction and initiate other chemical reactions, such as caramelization, pyrolysis and Strecker degradation, that produce more flavor compounds and volatile gases. The development stage is important for determining the roast degree and profile of the coffee.
There are different types of roasters that can be used for coffee roasting, such as drum roasters, fluidized bed roasters, hot air roasters and microwave roasters. Each type of roaster has its own advantages and disadvantages in terms of heat transfer, temperature control, airflow control, batch size, roast uniformity, energy efficiency and environmental impact. Roasters can also be classified as batch roasters or continuous roasters, depending on whether they roast one batch of beans at a time or continuously feed beans into the roasting chamber.
Controlling the Roast Profile
There are different methods of measuring and controlling the roast degree and profile of coffee, such as color measurement, weight loss measurement, sound analysis, gas analysis and sensory evaluation. Each method has its own limitations and challenges in terms of accuracy, reliability, repeatability and practicality. Roasters can also use different roast curves or graphs that plot the temperature or other variables against time to monitor and adjust the roasting process.
There are different styles or levels of coffee roasting, such as light roast, medium roast, dark roast and specialty roast. Each style or level has its own characteristics in terms of color, flavor, aroma, acidity, body and bitterness. Roasters can also create different blends or mixes of roasted beans from different origins or varieties to achieve different tastes or qualities.
Dark Roasted Coffee Beans
Dark roasted coffees are coffees that have been roasted well into or past the second crack stage, resulting in a dark brown or almost black color and a shiny, oily surface. Dark roasted coffees have a heavy body, low acid, and deep, sweet flavor notes, often resembling roasted nuts, dark chocolate, caramel, burned butter, and tobacco. Dark roasted coffees are also a source of antioxidants and caffeine, which may have benefits for cancer prevention and brain health.
Some examples of dark roasted coffees are French roast, Italian roast, Spanish roast, Vienna roast and espresso roast. Dark roasted coffees are suitable for brewing methods that use high pressure or longer contact time, such as espresso machines, moka pots and French presses. Dark roasted coffees are also popular for blending with milk or cream to create drinks like lattes, cappuccinos and mochas.
Coffee roasting is an art and a science that requires skill, knowledge and experience. Roasters can use different techniques or strategies to optimize the quality and consistency of their roasted coffee, such as preheating, preblending, precooling, postblending, quenching, resting and packaging. Roasters can also experiment with different parameters or factors to modify or enhance the flavor or aroma of their roasted coffee, such as charge temperature, charge weight, drop temperature, drop time, roast time ratio (RTR), rate of rise (RoR), development time ratio (DTR), airflow rate (AFR), drum speed (DS), bean agitation (BA), bean density (BD), bean moisture (BM), bean origin (BO) and bean variety (BV).
This guide is intended to provide a general overview of coffee roasting techniques based on some common sources. However, it is not exhaustive or definitive. Roasters should always consult more specific or updated sources for more detailed or accurate information. Roasters should also always use their own judgment and preference when roasting coffee.