Coffee roasting

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Process

The coffee roasting process consists essentially of sorting, roasting, cooling, and packaging operations but can also include grinding in larger scale roasting houses. 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 3 to 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 either batch or continuous modes and can be indirect- or direct-fired.

Those who roast coffee often prefer to follow a "recipe" or "roast profile" to highlight certain flavor characteristics. 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. abrasive blasting equipment

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, the roasted beans are cooled using a vacuum system. Roasted coffee beans are also cooled using fine water mist, which is known as "quenching" and is considered inferior to air cooling as the water soaks the fresh beans with moisture and oxygen particles making it stale almost instantly. Following roasting, the beans are cooled and stabilized. This stabilization process is called degassing. Following degassing, the roasted beans are packaged, usually in light-resistant foil bags fitted with small one-way valves to allow gasses to escape while protecting the beans from moisture and oxygen. Roasted whole beans can be considered fresh for up to one month. Once coffee is ground it is best used immediately. crankshaft grinding

Packaging cnc water jet

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. However, because coffee emits CO2 after roasting, coffee to be vacuum packed must be allowed to degas for several days before it is sealed. To allow more immediate packaging, pressurized canisters or foil-lined bags with pressure-relief valves can be used.

Darkness

As the bean absorbs heat, the color shifts to yellow and then to varying shades of brown. During the later stages of 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 eclipsed 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.

Below, roast levels and their respective flavors are described. These are qualitative descriptions, and thus subjective. As a rule of thumb, the "shinier" the bean is, the more dominant the roasting flavors are.

Roast level

Notes

Surface

Flavor

Light

Cinnamon roast, half city, New England

After several minutes the beans op or "crack" and visibly expand in size. This stage is called first crack. American mass-market roasters typically stop here.

Dry

Lighter-bodied, higher acidity, no obvious roast flavor

Medium

Full city, American, regular, breakfast, brown

After a few short minutes the beans reach this roast, which U.S. specialty sellers tend to prefer.

Dry

Sweeter than light roast; more body exhibiting more balance in acid, aroma, and complexity.

Full Roast

High, Viennese, Italian Espresso, Continental

After a few more minutes the beans begin popping again, and oils rise to the surface. This is called second crack.

Slightly shiny

Somewhat spicy; complexity is traded for heavier body/mouth-feel. Aromas and flavors of roast become clearly evident.

Double Roast

French

After a few more minutes or so the beans begin to smoke. The bean sugars begin to carbonize.

Very oily

Smokey-sweet; light bodied, but quite intense. None of the inherent flavors of the bean are recognisable.

Grades of coffee roasting; from left: unroasted (or "green"), light, cinnamon, medium, high, city, full city, Italian, and French.

Home roasting

Main article: Home roasting coffee

Home roasting is the process of roasting small batches of green coffee beans for personal consumption. Roasting coffee in the home is something that has been practiced for centuries, and has included methods such as heating over fire coals, roasting in cast iron pans, and rotating iron drums over a fire or coal bed. Computerized drum roasters are available which simplify home roasting and some home roasters simply roast in an oven or in air popcorn poppers.

Up until the 20th century, it was more common for at-home coffee drinkers to roast their coffee in their residence than it was to buy roasted coffee. During the 20th century, home roasting faded in popularity with the rise of the commercial coffee roasting companies. In recent years home roasting of coffee has seen a revival. In some cases there is an economic advantage, but primarily it is a means to achieve finer control over the quality and characteristics of the finished product.

Emissions and control

Particulate matter (PM), volatile organic compounds (VOC), organic acids, and combustion products are the principal emissions from coffee processing. Several operations are sources of PM emissions, including the cleaning and destoning equipment, roaster, cooler, and instant coffee drying equipment. The roaster is the main source of gaseous pollutants, including alcohols, aldehydes, organic acids, and nitrogen and sulfur compounds. Because roasters are typically natural gas-fired, carbon monoxide (CO) and carbon dioxide (CO2) emissions result from fuel combustion. Decaffeination and instant coffee extraction and drying operations may also be sources of small amounts of VOC. Emissions from the grinding and packaging operations typically are not vented to the atmosphere.

Particulate matter emissions from the roasting and cooling operations are typically ducted to cyclones before being emitted to the atmosphere. Gaseous emissions from roasting operations are typically ducted to a thermal oxidiser or thermal catalytic oxidiser following PM removal by a cyclone. Some facilities use the burners that heat the roaster as thermal oxidisers. However, separate thermal oxidisers are more efficient because the desired operating temperature is typically between 650C and 816C (1200F and 1500F), which is 93C to 260C (200F to 500F) more than the maximum temperature of most roasters. Some facilities use thermal catalytic oxidizers, which require lower operating temperatures to achieve control efficiencies that are equivalent to standard thermal oxidisers. Catalysts are also used to improve the control efficiency of systems in which the roaster exhaust is ducted to the burners that heat the roaster. Emissions from spray dryers are typically controlled by a cyclone followed by a wet scrubber.

Gallery

Unroasted coffee beans at various stages L: one year after drying, after drying, fresh picked.

Unroasted coffee beans at later stages. The beans are 7 and 8 years old.

An old large-capacity coffee roaster made from cast iron.

An example of lighter roasted, versus darker roasted beans. The degree of roasting which is ideal for coffee in general, and a given varietal or blend is highly subjective.

See also

Coffee

Dry roasting

French press

Torrefacto

v  d  e

Coffee

Production by country

Brazil  Colombia  Costa Rica  Ecuador  El Salvador  Ethiopia  Guatemala  Haiti  India  Indonesia  Jamaica  Kenya  Papua New Guinea  Philippines   USA  Vietnam

Coffee topics

History of coffee  Economics of coffee  Coffee and health  Coffee and the environment

Species and varieties

List of varieties  Coffea arabica: Kenya AA, Kona, Jamaican Blue Mountain  Coffea canephora (Coffea robusta): Kopi Luwak  Coffea liberica: Kape Barako  Single-origin

Major chemicals in coffee

Cafestol  Caffeic acid  Caffeine

Coffee processing

Coffee roasting  Decaffeination  Home roasting coffee

Coffee preparation

Coffeemaker  Coffee percolator  Espresso (lungo, ristretto)  Espresso machine  Drip brew  French press  Turkish coffee  Vacuum coffee maker  Instant coffee  Chemex  Moka pot  AeroPress  Presso  Knockbox

Popular coffee beverages

Affogato  Americano  Bicerin  C ph s   Caf au lait  Caf con leche  Caf Cubano  Cafe mocha  Caff corretto  Caff macchiato  Cappuccino  Carajillo  Coffee milk  Cortado  Espresso  Flat white  Frappuccino  Galo  Greek frapp coffee  Iced coffee  Indian filter coffee  Ipoh white coffee  Irish coffee  Latte  Latte macchiato  Liqueur coffee  Long black  Red eye  Ristretto

Coffee substitutes

Barley tea  Barleycup  Caro  Chicory  Dandelion coffee  Pero  Postum  Roasted grain beverage

Coffee and lifestyle

Barista  Caf  Caff  Caff sospeso  Coffee break  Coffee ceremony  Coffee culture  Coffee cupping  Coffee Palace  Coffeehouse  Fika  Kopi tiam  List of coffeehouse chains  Viennese caf

Notes and references

^ Spiller, Gene (9 October 1997). Caffeine. Los Altos, California, USA: SPHERA Foundation. pp. 85. doi:http://books.google.nl/books?hl=nl&lr=&id=Rgs_rVOceZwC&oi=fnd&pg=PA79&dq=darkness+coffee+roasting+full+city&ots=Ev9xikg8-G&sig=bsEFmf_McYD-vZllruUuMdsErFc#v=onepage&q=full%20city&f=false. ISBN 9780849326479. 

^ "Strong, or just burnt?", "Roast & Post". Accessed October 7, 2008.

^ Thompson, Tom (2009). "An Updated Pictorial Guide to the Roast Process". http://www.sweetmarias.com/roasting-VisualGuideV2.php. Retrieved 12 Januari 2010. 

^ http://www.epa.gov/ttn/chief/ap42/ch09/final/c9s13-2.pdf

Categories: Coffee preparation