coffee roasting

File:Coffee roaster from Baghdad, 15th century.jpg]]

File:Free standing tin coffee roaster - DPLA - ab92df8478ed695bac532e581df00ba5 (cropped).jpg

The first known implements for roasting coffee beans were thin, circular, often perforated pans made from metal or porcelain, used in the 15th century in the Ottoman Empire and Greater Persia. This type of shallow, dished pan was equipped with a long handle so that it could be held over a brazier (a container of hot coals) until the coffee was roasted. The beans were stirred with a slender spoon. Only a small amount of beans could be heated at one time.{{cite book |first=William Harrison |last=Ukers |year=1922 |title=All About Coffee |page=[https://archive.org/details/AllAboutCoffee/page/n683 615] |publisher=Tea and Coffee Trade Journal Company |url=https://archive.org/details/AllAboutCoffee}} The first cylinder roaster with a crank to keep the beans in motion appeared in Cairo around 1650. It was made of metal, most commonly tinned copper or cast iron, and was held over a brazier or open fire. French, Dutch and Italian variations of this design quickly appeared. These proved popular over the next century in Europe, England and the American colonies.Ukers 1922, pp. 616–618

In the 19th century, various patents were awarded in the U.S. and Europe for commercial roasters, to allow for large batches of coffee. Nevertheless, home roasting continued to be popular. A man working at a commercial roasting plant beginning in the 1850s in St. Louis, Missouri, said that "selling roasted coffee was up-hill work, as everyone roasted coffee in the kitchen oven."Ukers 1922, p. 631 Appliances catering to the home roaster were developed; in 1849 a spherical coffee roaster was invented in Cincinnati, Ohio, for use on the top of a wood-fired kitchen stove, fitted into a burner opening. Green beans were available at the local general store, or even through mail order. For roasting, many people used such simple methods as a layer of beans on a metal sheet in the oven, or beans stirred in a cast-iron skillet over a fire. Despite the wide popularity of home roasting, Burns felt that it would soon disappear because of the great strides made in commercial roasting in the 1860s and 1870s, including the benefits of the economies of scale. The commercial roaster inventions patented by Burns revolutionized the U.S. roasting industry,Ukers 1922, p. 634 much like the innovations of inventors in Emmerich am Rhein greatly advanced commercial coffee roasting in Germany.Ukers 1922, pp. 638–639 As well, the 1864 marketing breakthrough of the Arbuckle Brothers in Philadelphia, introducing the convenient one-pound (0.45 kg) paper bag of roasted coffee, brought success and imitators.{{cite book |last=Pendergrast |first=Mark |title=Uncommon Grounds: The History of Coffee and How It Transformed Our World |year=2010 |page=48 |publisher=Basic Books |isbn=978-0465024049}} From that time commercially roasted coffee grew in popularity until it gradually overtook home roasting during the 1900s in America.{{cite journal |journal=Tiny Joy |date=November 2013 |last=Owen |first=Tom |title=The Home Roasting Tradition |pages=1–2 |publisher=Sweet Maria's Coffee}} In 1903 and 1906 the first electric roasters were patented in the U.S. and Germany, respectively; these commercial devices eliminated the problem of smoke or fuel vapor imparting a bad taste to the coffee.Ukers 1922, p. 647 In France, the home roaster did not yield to the commercial roaster until after the 1920s, especially in rural areas. Coffee was roasted to a dark color in small batches at home and by shopkeepers, using a variety of appliances including ones with a rotating cylinder of glass, sheet iron or wire mesh, and ones driven by hand, clockwork or electric motor. Because of the smoke and blowing chaff, country dwellers generally roasted outdoors.Ukers 1922, pp. 646, 678

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In the 1950s just as instant coffee was becoming a popular coffee drink, speciality coffee-houses began opening to cater to the connoisseur, offering a more traditionally brewed beverage. In the 1970s, more speciality coffee houses were founded, ones that offered a variety of roasts and beans from around the world. In the 1980s and 1990s, the gourmet coffee industry experienced great growth.{{cite book |url=https://books.google.com/books?id=Hy0YIUYybOsC&pg=PA110 |page=110 |title=The Little Book of Coffee Law |last=Robertson |first=Carol |publisher=American Bar Association |year=2010 |isbn=978-1616327965}} Through the 1970s and 1980s, the Siemens Sirocco home roaster was made in West Germany and marketed globally. It was a small fluid-bed roaster made for the home enthusiast. The product was named after a commercial hot-air roasting process which itself was named after the hot Sahara winds called sirocco.Davids, 2003, p. 126. In 1976, chemical engineer Michael Sivetz patented a competing hot air design for manufacture in the U.S.; this became popular as an economical alternative. Sivetz called for the home roaster to focus on the quality of the bean.Pendergrast 2010, p. 296. From 1986 through 1999 there was a surge in the number of patents filed for home roasting appliances.{{cite book |title=Coffee: Recent Developments |first1=Ronald |last1=Clarke |first2=O. G. |last2=Vitzthum |publisher=John Wiley & Sons |year=2008 |page=104 |isbn=978-0470680216}} In the 1990s, more electric home roasting equipment became available, including drum roasters, and variations on the fluid-bed roaster. By 2001, gourmet coffee aficionados were using the internet to purchase green estate-grown beans for delivery by mail.{{cite book |first=Kevin |last=Sinnott |title=The Art and Craft of Coffee: An Enthusiast's Guide to Selecting, Roasting, and Brewing Exquisite Coffee |publisher=Quarry Books |year=2010 |isbn=978-1592535637 |pages=42, 60}}

The coffee-roasting process follows coffee processing and precedes coffee brewing. It consists essentially of sorting, roasting, cooling, and packaging but can also include grinding. 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 manually, by belt, or pneumatic conveyor to storage hoppers. From the storage hoppers, the green beans are conveyed to the roaster.

Initially, the process is endothermic (absorbing heat), but at around {{convert|175|°C|°F}} it becomes exothermic (giving off heat).Raemy A, Lambelet P. A calorimetric study of self-heating in coffee and chicory. Int J Food Sci & Tech, 1982;17(4):451–460. For the roaster, this means that the beans are heating themselves and an adjustment of the roaster's heat source might be required. At the end of the roasting cycle, the roasted beans are dumped from the roasting chamber and are typically cooled by air or water-quenching.

During the roasting process, coffee beans lose 15 to 18% of their mass due mainly to the loss of water but also to volatile compounds. Although the beans experience a weight loss, the size of the beans double during the roasting process due to the physical expansion caused by an increase in internal pressure from vaporized water.{{Cite book |title=Espresso coffee : the science of quality |date=2005 |publisher=Elsevier Academic |editor=Andrea Illy |editor2=Rinantonio Viani |isbn=0-12-370371-9 |edition=2nd |location=Amsterdam |oclc=57592120}} Green coffee can contain reasonable quantities of simple sugars. Sugars are quite reactive at roasting temperatures and, once the water has evaporated out of the bean, the sugars can begin to react to the heat in different ways. Some go through caramelization reactions, creating the caramel notes found in certain coffees.{{Cite book|last=Hoffmann|first=James|title=The World Atlas of Coffee 2nd Edition|publisher=Mitchell Beazley|year=2018|isbn=978-1-78472-429-0|location=Great Britain|pages=59|language=English}}

There are several traditional variations to coffee roasting in different parts of the world. For example, in Vietnam coffee is often coated with oil (traditionally clarified butter) and a small amount of sugar prior to roasting to produce a "butter roast". The roasting process results in an additional caramelized coating on the beans.{{cite news |title=Asia's best coffee – Vietnam |date=November 6, 2009 |last=Eckhardt |first=Robyn |newspaper=The Wall Street Journal |url=https://www.wsj.com/articles/SB125739786129330315 |url-access=subscription |access-date=2014-12-02 |url-status=live |archive-url=https://web.archive.org/web/20150427212719/http://www.wsj.com/articles/SB125739786129330315 |archive-date=April 27, 2015}}

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The most common roasting machines are of two basic types: drum and hot-air, although there are others including packed-bed, tangential and centrifugal roasters. Roasters can operate in either batch or continuous modes. Home roasters are also available.{{Cite book|last=Sivetz|first=Michael|url=https://www.worldcat.org/oclc/4804343|title=Coffee technology|date=1979|publisher=AVI Pub. Co|others=Norman W. Desrosier|isbn=0-87055-269-4|location=Westport, Conn.|oclc=4804343}}

Drum machines consist of horizontal rotating drums that tumble the green coffee beans in a heated environment. The heat source can be supplied by natural gas, liquefied petroleum gas (LPG), electricity, or even wood. The most common employ indirectly heated drums where the heat source is under the drum. Direct-fired roasters are roasters in which a flame contacts the beans inside the drum; very few of these machines are still in operation.{{Cite book|last=Roast Magazine|url=https://www.worldcat.org/oclc/1006391141|title=The book of roast.|date=2017|publisher=JC Publishing, Inc|isbn=978-0-9987717-0-0|volume=p:461|location=Portland, Oregon|oclc=1006391141}}

Fluid bed or hot-air roasters force heated air through a screen or perforated plate under the coffee beans with sufficient force to lift the beans. Heat is transferred to the beans as they tumble and circulate within this fluidized bed.{{Cite book|url=https://www.worldcat.org/oclc/214281450|title=Coffee : recent developments|date=2001|publisher=Blackwell Science|others=R. J. Clarke, O. G. Vitzthum|isbn=978-0-470-69049-9|location=Oxford|oclc=214281450}}

{{more citations needed|section|date=July 2016}}

Image:0 Monschau - Stadtstraße 24 - Vitrine.JPG (Germany)]]

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Some coffee roasters use names for the various 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.{{Cite web|url=http://www.ncausa.org/About-Coffee/Coffee-Roasts-Guide|title=Coffee Roasts Guide|url-status=live|archive-url=https://web.archive.org/web/20160926112131/http://www.ncausa.org/about-coffee/coffee-roasts-guide|archive-date=2016-09-26}}File:Roasting Coffee Progression.pngOne method of determining the degree of roast is to evaluate the bean's color. 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.{{Cite web |title=Il mio ricordo di Gianni Frasi. Nei chicchi di caffè aveva condensato la vita |url=https://www.identitagolose.it/sito/it/44/21360/dallitalia/il-mio-ricordo-di-gianni-frasi-nei-chicchi-di-caffe-aveva-condensato-la-vita.html |access-date=2023-08-29 |website=Identità Golose Web: magazine italiano di cucina internazionale |language=it}}{{Cite book |last=Farinotti |first=Luca |title=Mondoristorante |publisher=Edizioni Clandestine |year=2018 |isbn=9788865967676 |location=Massa, Italy}} It is common for roasters to use a combination of temperature, smell, color, and sound to monitor the roasting process. The famous Italian roaster Gianni Frasi explains how artisanal roasting is fundamental in order to obtain a high quality coffee ("immersion in direct flame is purification, it makes a dead bean alive", "the bean's dignity can only be guaranteed by an open flame"{{Cite web |last=Rosso |first=Gambero |date=2018-12-07 |title=Muore Gianni Frasi del Caffè Giamaica: il torrefattore degli chef |url=https://www.gamberorosso.it/notizie/e-morto-gianni-frasi-il-torrefattore-del-caffe-giamaica-che-sussurrava-agli-chef/ |access-date=2023-08-29 |website=Gambero Rosso |language=it-IT}}). Also according to Frasi, the bean can be defined as perfectly toasted when it takes on a particular "friar's tunic" color nuance which can only be obtained in a precise instant of the process and which the craftsman must be able to grasp by sight. This particular coloring is proof that all the potential aromas of the green bean have been released. The craft system was codified by Italian author Luca Farinotti{{Cite web |author= |title=#mondoristorante – Luca Farinotti |url=https://www.mondadoristore.it/mondoristorante-Luca-Farinotti/eai978886596767/ |access-date=2023-08-29 |website=www.mondadoristore.it/ |language=it-it}} in his 2019 award-winning book{{Cite web |last=admin |date=2019-04-11 |title=PREMIO SELEZIONE BANCARELLA DELLA CUCINA 2019 |url=https://www.premiobancarella.it/site/?p=2222 |access-date=2023-08-29 |website=Premio Bancarella – Pontremoli – Lunigiana |language=it-IT}} World and restaurant.

There are two events called "cracks" that roasters listen for. At approximately {{convert|196|°C|°F}}, the coffee will emit a cracking sound. This point is referred to as "first crack", marking the beginnings of a very light roast. At first crack, a large amount of the coffee's moisture has been evaporated and the beans will begin to increase in size. When the coffee reaches approximately {{convert|224|°C|°F}}, it emits a "second crack". This sound represents the structure of the coffee becoming brittle and fracturing as the bean continues to swell and enlarge from internal pressure. If the roast is allowed to progress further, it begins to take on the characteristics of the roasting process and loses the characteristics of the coffee's origin.{{Cite book|last=Rao|first=Scott|url=https://www.worldcat.org/oclc/888216257|title=The coffee roaster's companion|date=2014|isbn=978-1-4951-1819-7|location=Canada|oclc=888216257}}

Lipids present inside the coffee seed liquify from heat and pressure built up in the bean. These lipids can often be seen on the bean surface. An oily coating is more prevalent with darker roasts.{{Cite book|url=https://www.worldcat.org/oclc/57592120|title=Espresso coffee : the science of quality|date=2005|publisher=Elsevier Academic|others=Andrea Illy, Rinantonio Viani|isbn=0-12-370371-9|edition=2nd|location=Amsterdam|oclc=57592120}}

These images depict samples taken from the same batch of a typical Brazilian green coffee at various bean temperatures with their subjective roast names and descriptions.{{cite web |url=http://www.coffeereview.com/glossary.cfm |title=Glossary of Coffee and Espresso Terms |publisher=Coffee Review |access-date=2012-07-28 |url-status=live |archive-url=https://web.archive.org/web/20120616164345/http://www.coffeereview.com/glossary.cfm |archive-date=2012-06-16 }}

At lighter roasts, the coffee will exhibit more of its "origin character"—the flavors created by its variety, processing, altitude, soil content, and weather conditions in the location where it was grown.{{Cite book| author =Gene Spiller | title = Caffeine | publisher = SPHERA Foundation | date = 9 October 1997 | location = Los Altos, California, USA | page = 85 | isbn = 978-0-8493-2647-9}} 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. Green coffee contains many different types of acids, some of which are pleasant to taste and some that are not. Of particular importance to the roaster are the chlorogenic acids (CGAs). One of the key goals of roasting is to break down these unpleasant acids.

Below, roast levels and their respective flavors are described. These are qualitative descriptions, and thus subjective.

Caffeine levels are not significantly affected by the level of roast.{{Cite journal|last1=Tfouni|first1=Silvia A. V.|last2=Carreiro|first2=Larissa B.|last3=Teles|first3=Camila R. A.|last4=Furlani|first4=Regina P. Z.|last5=Cipolli|first5=Katia M. V. A. B.|last6=Camargo|first6=Mônica C. R.|date=March 2014|title=Caffeine and chlorogenic acids intake from coffee brew: influence of roasting degree and brewing procedure|url=http://doi.wiley.com/10.1111/ijfs.12361|journal=International Journal of Food Science & Technology|language=en|volume=49|issue=3|pages=747–752|doi=10.1111/ijfs.12361}}{{Cite journal|last1=Hečimović|first1=Ivana|last2=Belščak-Cvitanović|first2=Ana|last3=Horžić|first3=Dunja|last4=Komes|first4=Draženka|date=December 2011|title=Comparative study of polyphenols and caffeine in different coffee varieties affected by the degree of roasting|url=https://linkinghub.elsevier.com/retrieve/pii/S030881461100762X|journal=Food Chemistry|language=en|volume=129|issue=3|pages=991–1000|doi=10.1016/j.foodchem.2011.05.059|pmid=25212328|url-access=subscription}} Caffeine remains stable up to {{convert|200|°C|°F}} and completely decomposes around {{convert|285|°C|°F}}.{{Cite journal|last1=Wang|first1=Rui|last2=Xue|first2=Jingjing|last3=Meng|first3=Lei|last4=Lee|first4=Jin-Wook|last5=Zhao|first5=Zipeng|last6=Sun|first6=Pengyu|last7=Cai|first7=Le|last8=Huang|first8=Tianyi|last9=Wang|first9=Zhengxu|last10=Wang|first10=Zhao-Kui|last11=Duan|first11=Yu|date=June 2019|title=Caffeine Improves the Performance and Thermal Stability of Perovskite Solar Cells|journal=Joule|language=en|volume=3|issue=6|pages=1464–1477|doi=10.1016/j.joule.2019.04.005|doi-access=free}} Given that roasting temperatures do not exceed {{convert|200|°C|°F}} for long and rarely if ever reach {{convert|285|°C|°F}}, the caffeine content of a coffee is not likely changed much by the roasting process.{{Cite journal|last1=Wahyuni|first1=N L E|last2=Rispiandi|first2=R|last3=Hariyadi|first3=T|date=2020-05-19|title=Effect of bean maturity and roasting temperature on chemical content of robusta coffee|journal=IOP Conference Series: Materials Science and Engineering|volume=830|issue=2|pages=022019|doi=10.1088/1757-899X/830/2/022019|bibcode=2020MS&E..830b2019W|issn=1757-899X|doi-access=free}}{{Cite journal|last1=Casal|first1=S.|last2=Beatriz Oliveira|first2=M.|last3=Ferreira|first3=Margarida A.|date=March 2000|title=HPLC/diode-array applied to the thermal degradation of trigonelline, nicotinic acid and caffeine in coffee|url=https://linkinghub.elsevier.com/retrieve/pii/S0308814699002289|journal=Food Chemistry|language=en|volume=68|issue=4|pages=481–485|doi=10.1016/S0308-8146(99)00228-9|url-access=subscription}}, cited in {{Cite book|url=https://www.worldcat.org/oclc/969828311|title=Achieving sustainable cultivation of coffee : breeding and quality traits|date=2018|others=Philippe Lashermes|isbn=978-1-78676-152-1|location=Philadelphia, PA|oclc=969828311|page=218}} Despite this, and the common misconception that darker roasts will always contain more caffeine than lighter roasts, when beans are roasted they lose water and expand. As a result, when ground and measured by volume, the denser lighter roast will contain more caffeine than the darker roast.{{Cite web |title=Caffeine Content of Coffee: Dark Roast vs. Light Roast |url=https://www.americastestkitchen.com/cooksillustrated/how_tos/8237-caffeine-content-of-coffee-dark-roast-vs-light-roast |access-date=June 24, 2024 |website=America's Test Kitchen}}{{Cite news |last=Lipka |first=Mitch |date=March 27, 2014 |title=Your money: Getting the biggest caffeine buzz for your buck |url=https://www.reuters.com/article/markets/wealth/your-money-getting-the-biggest-caffeine-buzz-for-your-buck-idUSBREA2P197/ |access-date=June 24, 2024 |work=Reuters}}

{{Main|Home roasting coffee}}

Home roasting is the process of roasting small batches of green coffee beans for personal consumption. Even after the turn of the 20th century, it was more common for at-home coffee drinkers to roast their coffee in their residence than it was to buy pre-roasted coffee. Later, 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.Davids, Kenneth. Home Coffee Roasting: Romance and Revival. St. Martin's Griffin; revised edition, November 2003. {{ISBN|978-0-312-31219-0}} 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.

Extending the shelf life of roasted coffee relies on maintaining an optimum environment to protect it from exposure to heat, oxygen, and light. Roasted coffee has an optimal typical shelf life of two weeks, and ground coffee about 15 minutes. Without some sort of preservation method, coffee becomes stale. The first large-scale preservation technique was vacuum packing in cans. However, because coffee emits CO₂ after roasting, coffee to be vacuum-packed must be allowed to de-gas 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. Refrigeration and freezing retards the staling process. Roasted whole beans can be considered fresh for up to one month if kept cool.{{Citation needed|date=November 2010}} Once coffee is ground it is best used immediately.

Particulate matter (PM), volatile organic compounds (VOC), organic acids, and combustion products are the principal emissions from coffee processing.{{cite book |chapter=9.13.2: Coffee Roasting |chapter-url=https://www3.epa.gov/ttn/chief/ap42/ch09/final/c9s13-2.pdf |title=AP-42: Compilation of Air Emissions Factors |url=https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors |website=EPA |access-date=2009-02-01 |url-status=live |archive-url=https://web.archive.org/web/20080724041404/http://www.epa.gov/ttn/chief/ap42/ch09/final/c9s13-2.pdf |archive-date=2008-07-24 }} 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 heated by combustion of natural gas, 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 {{convert|650|-|816|°C|°F}}, which is {{convert|93|-|260|°C|°F}} 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.

File:Diedrich IR Series Coffee Roaster.jpg|An Electrical Coffee Roaster

File:Coffeeroasting woodfired.jpg|An old wood-fired coffee roaster

File:Coffee Roaster.JPG|A two-barrel coffee roaster for roasting coffee samples prior to purchasing or roasting green coffee beans

File:2013 Antique sample roasting machine Vits Munchen.jpg|An antique "Mignon" five-barrel test roasting machine

File:Probat Roasters.jpg|The roasting room at a midsize coffee company

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