Coffee Roasting

The Coffee Roasting  Process

If you were to brew a Coffee from beans as they ship from the growers, you’d find that the coffee would have no flavor and no aroma. This is because all of the flavor and aroma that we enjoy in coffee is created by the coffee bean roasting process.

Roasting coffee transforms the chemical and physical properties of green coffee beans into roasted coffee products. And without roasting, we would not have coffee as we know it today. When roasted, the green coffee bean expands to nearly double its original size, changing in color, taste, smell and density. Unroasted beans contain all of coffee’s acids, protein, and caffeine, but none of coffee’s taste. It takes heat to start the chemical reactions that turn the carbohydrates and fats into aromatic oils, burn off moisture and carbon dioxide, and to break down & build up acids. The end result is the characteristic coffee flavor that we all enjoy.

Green coffee is more stable than roasted coffee and the closer the roasting process is to where the coffee will be consumed, the fresher the coffee will be. But don’t discount commercial coffees just because they were roasted months ago and half a country away. The commercial coffee roasters address coffee freshness through innovative and creative packaging solutions that drastically slow down the coffee’s aging process. But even with modern packing and distribution, some coffee drinkers still roast coffee themselves in order to have more control over the freshness and roast level of the beans.

The coffee roasting process consists essentially of cleaning, roasting, cooling, grinding, and packaging operations. In larger operations, bags of green coffee beans are hand or machine-opened, dumped into a hopper, and screened to remove debris. The green beans are then weighed and transferred by belt or pneumatic conveyor to storage hoppers. From the storage hoppers, the green beans are conveyed to the roaster. Roasters typically operate at temperatures between 370 and 540 °F (188 and 282 °C), and the beans are roasted for a period of time ranging from a few minutes to about 30 minutes. Roasters are typically horizontal rotating drums that are heated from below and tumble the green coffee beans in a current of hot gases. The heat source can be supplied by natural gas, Liquefied petroleum gas (LPG), electricity or even wood. These roasters can operate in batch or continuous modes and can be indirect or direct-fired.

Many people who roast coffee prefer to follow a "recipe", or roast profile, when bringing out the flavor characteristics they wish to highlight. Any number of factors may help a person determine the best profile to use, such as the coffee's origin, varietal, processing method or desired flavor characteristics. A roast profile can be presented as a graph showing time on one axis and temperature on the other, which can be recorded manually or using computer software and data loggers linked to temperature probes inside various parts of the roaster.

Indirect-fired roasters are roasters in which the burner flame does not contact the coffee beans, although the combustion gases from the burner do contact the beans. Direct-fired roasters contact the beans with the burner flame and the combustion gases. At the end of the roasting cycle, water sprays are used to "quench" the beans. Following roasting, the beans are cooled and run through a "de-stoner". De-stoners are air classifiers that remove stones, metal fragments, and other waste not removed during initial screening from the beans. The de-stoners pneumatically convey the beans to a hopper, where the beans are stabilized and dried. This stabilization process is called equilibration. Following equilibration, the roasted beans are ground or packaged as whole beans. Roasted whole beans can be considered fresh for up to, but not exceeding one month. Once coffee is ground it is best used within 24 hours.

Packaging

Extending the useful life of roasted coffee relies on maintaining an optimum environment for the beans. The first large scale preservation technique was vacuum packing. But because coffee emits CO2 after roasting, coffee had to wait for several days to de-gas before vacuum packaging and sealing. To allow more immediate packaging, pressurized canisters or foil-lined bags with pressure-relief valves were developed. The pressure relief valve allows the CO2 gas to escape without letting oxygen into the package. Both of these methods are commonly used in the States to extend the life of ground coffee destined for grocery stores and between the two, vacuum packaging provides the longest shelf life. Commercial coffee is usually distributed in a nitrogen flushed bags. Any one of these methods greatly extend the shelf life of ground coffee by depriving the coffee of oxygen.

Darkness

As the bean absorbs heat, the color shifts to yellow and then to a light "cinnamon" brown then to a dark brown. During roasting, oils appear on the surface of the bean, making it shiny. The roast will continue to darken until it is removed from the heat source.

At lighter roasts, the bean will exhibit more of its "origin flavor" - the flavors created in the bean by the soil and weather conditions in the location where it was grown. Coffee beans from famous regions like Java, Kenya, Hawaiian Kona, and Jamaican Blue Mountain are usually roasted lightly so their signature characteristics dominate the flavor. As the beans darken to a deep brown, the origin flavors of the bean are slowly replaced by the flavors created by the roasting process itself. At darker roasts, the "roast flavor" is so dominant that it can be difficult to distinguish the origin of the beans used in the roast. Roasted coffee beans are sold by the degree of roast, ranging from "Light Cinnamon Roast" through "Vienna Roast" to "French Roast" and beyond.

A note on flavor: Describing the tastes of different roasts is as subjective as putting a wine into words. In both cases there’s no substitute for your own personal taste. As a guide, if you can see the oil on the beans as in the image above, you are more likely to taste the roasting flavors, than the individual characteristics of the beans.

Roasting is one part art, one part science, and several parts judgment. It is a skill. Too much heat and the beans are roasted too dark and too much caffeol (aromatic oil produced by roasting coffee) is burnt; not enough and the caffeol is not precipitated. In industrial quantities, the process is carefully controlled and the quality is very consistent, but in smaller quantities, quality is completely in the hands of the roaster. The higher the roast, the more uniform the resulting flavor.

The different kinds of roast include light or low, medium and dark or high, while various other terns, such as European, are used in the USA. Some beans are more appropriate for certain roasts. A light Ethiopian bean would lose its character if it was high roasted, while some Mexican beans can benefit from a high roast.