Roasting green coffee is the process of heating, cooking or drying coffee beans in a coffee roaster in order to transform the physical and chemical properties of the green coffee beans so the desired flavors and aromas of the final cup of brewed coffee can be achieved.
Roast level does not significantly change the caffeine levels.
Caffeine did not undergo significant degradation with only 5.4% being lost under severe roasting.
Chemical Reactions of Roasting - Pyrolisis
Roasting eliminates most of the moisture in the coffee beans and begins a series of chemical reactions known as pyrolisis, changing the chemical composition of the coffee and developing the compounds associated with the flavors and aromas of the brewed coffee.
The Skills of the Roastmaster
The skilled roastmaster strives to apply the proper temperature for just the right amount of time to bring out the best flavors of the particular coffee beans being roasted.
Roastmasters pay close attention to the color level of the roasting coffee beans as they expand and change color, ranging from very light to very dark. As the coffee beans lose moisture, their density also changes.
Effects of Coffee Roasting
Coffee Roasters, Roasting Temperature, and Roasting Time
Roasting coffee requires skill as well as a proper coffee roaster. A typical roasting temperature ranges from 370 to 540 °F (188 to 282 °C).
Roasting times vary from about 8 to 20 minutes depending on the size of the roaster and variety, and the beans shrink about 20% by weight as they gain a dark hue and fragrant aroma. Twenty-five pounds of green coffee beans may take about fifteen minutes to roast.
As an example, it takes about eight pounds of coffee cherry to make one pound of roasted coffee (100 lbs. of coffee cherry produces approximately 12 lbs. of roasted coffee).
Caramelization During the Roasting Process
Caramelization is the process that occurs during a certain stage of coffee roasting when simple sugars in the coffee beans are heated to a particular temperature, creating a caramel flavor and color.
Carbon dioxide is a gas that forms in coffee beans during the roasting process; a natural byproduct of coffee roasting. The process of carbon dioxide gases releasing from freshly roasted coffee is known as degassing.
Millstone Slow Coffee Roasting
A custom coffee roasting technique called Millstone Slow is accomplished by the roastmaster listening carefully for distinct popping sounds as the coffee beans expand. This is done in small batches, with the roastmaster carefully sampling each batch to make sure the perfect roast level is being achieved.
Continuous Fluidized Bed Roasting
The process of roasting coffee beans by levitating the beans on a cushion of hot air is known as continuous fluidized bed roasting.
Often used during the process of making instant coffee, continuous fluidized bed roasting takes from 30 seconds to 4 minutes and uses lower temperatures. The benefit of lower temperatures is better taste and aroma retention.
Factors Affecting Coffee Roasting Time
Total roasting time for whole bean coffee varies depending upon numerous factors such as the the type of roast required, the quality of the coffee beans, their moisture content, and grade. Also affecting roasting time is the age of the coffee beans as well as the weather conditions where the roasting is being done.
The roastmaster pays attention to the roasting time and temperature as well as more subtle considerations such as the appearance and smell of the coffee during roasting.
First Crack and Second Crack
The roastmaster also listens for the popping sounds of the roasting coffee. These distinct “cracks” of the coffee beans occur at particular roasting stages, and there is a first crack and a second crack.
The first crack occurs at about 385 to 400 degrees Fahrenheit, typically just several minutes after the roasting begins. The coffee beans visibly expand in size as they crack, crackle, or pop. Light Roast are roasted only until the first crack.
The second crack occurs when the coffee beans reach about 440 to 450 degrees Fahrenheit and the cellulose matrix of the coffee begins to break down.
This occurs usually several minutes after the first crack as the coffee beans once again, crack, crackle, or pop. Coffee beans roasted just to this point are usually considered a Full Roast (Medium-Dark Roast).
Dark Roasts - Denoting the Full Development of the Coffee Beans
Coffee beans roasted to the second crack will be slightly shiny as oils begin rising to the surface. This denotes the full development of the coffee, and the flavor will be spicy, with a heavier body than a Light Roast or Medium Roast. The roast flavor is evident.
Coffee Roast Profiles - Standardization in the Roasting Industry
In general there is very little standardization in coffee roasting (e.g., roast types, roast profiles, and how the various roasts are produced). The roast profile of a coffee is a graph of the temperature of the coffee beans during the time of the coffee roasting.
The Four Primary Types of Roasts
The primary factor in determining roasting time is the type of roast required, and these can be generally divided into four types ranging from Light Roast to Medium Roast to Medium-Dark Roast to Dark Roast.
Light Roasts are also referred to as Cinnamon Roast, Half City Roast, Light City Roast, and New England Roast.
Medium Roast s are also referred to as American Roast, Breakfast Roast, Brown Roast, City Roast, Medium-Brown Roast, Medium High Roast, Regular Roast, and Standard American Roast.
Medium-Dark Roasts include After-Dinner Roast, Dark-Brown Roast, Full-City Roast, Full Roast, Light Espresso Roast, Light French Roast, High Roast, North Italian Roast, and Viennese Roast.
Dark Roasts are also referred to as Black-Brown Roast, Continental Roast, Dark French Roast, Double Roast, Espresso Roast, European Roast, French Roast, Heavy Roast, Italian Roast, Italian Espresso Roast, Neapolitan Roast, New Orleans Roast, South Italian Roast, Spanish Roast, Turkish Roast, Very Dark-Brown Roast, and Vienna Roast.
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