Roasting coffee transforms the chemical and physical properties of green coffees into roasted coffee products. The roasting procedure is what produces the characteristic flavor of coffee by causing the green coffees to improve in taste. Unroasted beans contain similar if not higher degrees of acids, protein, sugars, and caffeine as people with been roasted, but lack the taste of roasted coffees because of the Maillard and other chemical reactions that happen during roasting.
Source: Stock coffee bags
Almost all coffee is roasted commercially on a big scale, but small-scale commercial roasting is continuing to grow significantly with the trend toward "single-origin" coffees served at specialty shops. Some coffee drinkers even roast coffee in the home as a hobby to be able to both test out the flavor profile of the beans and make sure the freshest possible roast.
The first recorded implements for roasting coffees were thin pans created from metal or porcelain, found in the 15th century in the Ottoman Empire and Greater Persia. In the 19th century, various patents had been awarded in the U.S. and Europe for commercial roasters, to permit for huge batches of coffee. In the 1950s just as instant coffee was learning to be a popular coffee drink, speciality coffee-houses began opening to focus on the connoisseur, supplying a more traditionally brewed beverage. In the 1970s, even more speciality coffee houses had been founded, ones that offered a number of roasts and beans from all over the world. In the 1980s and 1990s, the gourmet coffee industry experienced great growth. This trend continued in to the 21st Century.
Process
The coffee-roasting process follows coffee processing and precedes coffee brewing. It consists essentially of sorting, roasting, cooling, and packaging but may also consist of grinding in larger-scale roasting houses. In larger operations, bags of green coffees are hand- or machine-opened, dumped right into a hopper, and screened to eliminate 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. At first, the procedure is endothermic (absorbing heat), but at around 175 °C (347 °F) it becomes exothermic (giving off heat). For the roaster, which means that the beans are heating themselves and an adjustment of the roaster's heat source may be required. By the end of the roasting cycle, the roasted beans are dumped from the roasting chamber and air cooled with a draft inducer.
Through the roasting process, coffees tend to proceed through a weight lack of about 15 to 18% because of the lack of water and volatile compounds. Although the beans encounter a weight loss, how big is the beans double following the roasting process because of the physical expansion of the cellulose structure which facilitates the release of skin tightening and, volatile organic compounds, and water (in the form of steam).
There are many traditional variations in bean roasting in various elements of the world. For instance, in Vietnam coffee is usually often coated with oil (traditionally clarified butter) and handful of sugar ahead of roasting to make a "butter roast". The roasting process results within an additional caramelized coating on the beans.
Roasts
Some coffee roasters use names for the many degrees of roast, such as "city roast" and "French roast", for the internal bean temperatures found during roasting. Recipes known as "roast profiles" indicate how to achieve flavor characteristics. Any number of factors may help a person determine the best profile to use, such as the coffee's origin, variety, processing method, moisture content, bean density, 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.
The most famous, but most likely the least accurate, approach to determining the amount of roast is to guage the bean's color by eye (the exception to this is using a spectrophotometer to measure the ground coffee reflectance under infrared light and comparing it to standards like the Agtron scale). As the coffee absorbs heat, the color shifts to yellow and then to increasingly darker shades of brown. During the later stages of roasting, oils appear on the surface of the bean. The roast will continue to darken until it is removed from the heat source. Coffee also darkens as it ages, making color alone a poor roast determinant. Most roasters use a combination of temperature, smell, color, and sound to monitor the roasting process.
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