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Coffee Roasting Basics: A Historical Perspective

Recently, many coffee roasting enthusiasts have emerged. Today, I'd like to recommend an introductory coffee roasting book called "Complete Guide to Home Coffee Roasting." The following is a portion of the content from this book...

Europeans first encountered coffee as a beverage in the 16th century in coffee houses across Syria, Egypt, and Turkey. They first saw coffee beans as seeds on the terraced fields of Yemen, located at the southern tip of the Arabian Peninsula. At that time, the renowned botanist Linnaeus began naming and classifying various plants of this new era, classifying the coffee trees here as "Coffea Arabica."

For centuries, Arabica coffee beans were the only commercially traded variety, and they remain the mainstream of world coffee trade today. However, according to Linnaeus's hypothesis, the origin of coffee trees was not the Arabian Peninsula region but rather the highland forests of central Ethiopia. This hypothesis was not confirmed by Western scientific communities until the mid-20th century. In Africa, Asia, and Madagascar, there are over 100 recognized wild coffee species, but only about 30 species are cultivated, mostly on a small scale. Among these is the variety called "Coffea Canephora," also known as "Coffea Robusta," which has become Arabica's main competitor in commercial trade and human consumption.

No one really knows where or when Arabica coffee beans were first cultivated. Some historians speculate that coffee trees were first cultivated in Yemen, but stronger evidence shows that in Ethiopia—the verified botanical origin of coffee—there were records of deliberate coffee tree cultivation around 575 AD. When brought to southern Arabia for cultivation, coffee was already an agricultural crop.

Additionally, no one can determine exactly how the earliest "cup of hot coffee" was defined. As we know, coffee beans are small seeds inside thin-fleshed, sweet fruits. The earliest "hot coffee" was not extracted from coffee beans at all. Instead, it was likely made by lightly roasting the coffee fruit husks and then directly boiling them in water to make "hot coffee"! Even today, this method of making hot drinks remains common in Yemen, where locals call it "Qishr" (also spelled Kishr, Kisher, and many other variations). In Europe, this beverage is called "Coffee Sultan" (also spelled Coffee Sultana). Another possibility is that dried fruits and seeds were roasted together, then ground and boiled in water. The dried fruit husk is very sweet and contains caffeine, so any beverage made from coffee fruit husks tastes sweet and has the stimulating effects of caffeine.

The Discovery of Coffee Roasting

A thought-provoking question: what would motivate someone from Syria, Persia, or Turkey to roast coffee seeds at sufficiently high temperatures to allow effective "pyrolysis," fully revealing the most reliable flavor oils in coffee beans? This background is undoubtedly the greatest reason for the successful cultivation of coffee culture's value!

Various theories exist about coffee's origins, ranging from imaginative and poetic explanations to seemingly plausible yet contrived accounts. According to Islamic legends, around 1260 AD, a man named Sheik Omar was exiled to the Arabian desert. To stave off hunger, he tried boiling coffee seeds directly into a soup, but found it bitter. Later, he roasted the seeds first before boiling them into soup.

Another theory suggests that farmers in Yemen or Ethiopia discovered the value of coffee seeds when using coffee branches as firewood. This theory appeared frequently in literature in the early 20th century, with its storytelling elements making it popular, though it has some historical inaccuracies.

In his provocative historical work "Coffee Floats, Tea Sinks," Ian Bersten hypothesizes that this was simply a spontaneous event. Someone accidentally discovered that lightly roasted coffee fruit husks produced a superior "Qishr" beverage compared to the original preparation method, so they continued this practice and also began roasting coffee seeds. Bersten boldly suggests that in the 16th century, when southern Arabia was under Ottoman Turkish rule, they promoted the practice of roasting coffee seeds to make "Qishr" beverages to utilize what had previously been considered useless coffee seeds.

Clearly, the Ottoman Turkish Empire was responsible for spreading coffee drinking habits and coffee preparation technology. The empire's continuous territorial expansion indirectly promoted cultural and commercial exchanges related to coffee consumption. Bersten further points out that Syria was the first region where true "roasted coffee" emerged. Syrians, particularly those in Damascus, developed metal utensils specifically for roasting coffee beans, which could achieve higher temperatures than the traditional clay roasting equipment used by Yemenis.

Moreover, Bersten believes that the aroma produced by roasting smoke—which only appears when pyrolysis begins, a fascinating smell even better than the taste of coffee itself—might be why someone persistently continued roasting coffee seeds. Those who did this regularly learned that coffee seeds must be roasted to fairly high temperatures for this aroma to emerge, and "Qishr" beverages made with roasted coffee seeds would then have fruit-like aromas.

These theories remain unconfirmed today. Many historical records indicate that humans had been roasting seeds and nuts long before they began roasting coffee seeds—partly to improve eating texture and partly to make them more digestible. Perhaps roasting coffee seeds was simply someone applying this existing practice. Another possibility is that someone preparing "Qishr" ingredients accidentally left them roasting for too long, and when they returned, discovered an unexpected delight when brewing this over-roasted ingredient.

Regardless, we can at least confirm that by around 1550 AD, in regions like Syria or Turkey, the term "roasted coffee beans" definitely existed. From this point onward, roasted coffee beans not only became a worldwide cultural phenomenon but also marked the beginning of prosperous commercial trade.

Coffee Roasting Rituals

Early "roasting" in the Arabian region was a very simple process. Although we lack sufficient historical materials to recreate this roasting process exactly, it was generally similar to the roasting methods still used in Arabia today. European historian William Palgrave, in his 1863 work "Narrative of a Year's Journey Through Central and Eastern Arabia," recorded the following description:

...Sowlin began preparing roasted coffee beans without hesitation. He spent about five minutes starting a fire with a blower and adjusting the charcoal to the optimal position to generate sufficient heat. Next, he took an old cloth bag tied with rope from a nearby niche. After untying the rope, he poured out three or four handfuls of unroasted coffee beans (still with their fruit husks intact) onto a large woven tray. He carefully sorted out blackened coffee seeds and other foreign objects (usually mixed in with purchased coffee cherries). After careful cleaning, he poured these green beans into a large iron ladle with a wide mouth and handle, then moved the ladle to the fire's edge. While using the blower to maintain stable heat, he repeatedly stirred the coffee beans until they produced cracking sounds, turned red, and emitted white smoke. Finally, just before the beans turned to charcoal, he carefully moved the ladle away from the heat source, then cooled the beans on a large woven tray using an ancient Turkish or European method...

In the Arabian Peninsula, the processes of roasting, grinding, brewing, and drinking coffee all took place in relaxed social gatherings. Roasting and brewing were both performed over the same fire. Coffee beans were stirred with a flat-ended metal rod during roasting. After cooling, the roasted beans were placed in a mortar and ground into coarse powder, then boiled with water, usually with cardamom or saffron added. After brewing, it was filtered once before being poured into cups and consumed without sugar.

Many variations of this coffee ritual exist throughout East Africa and the Middle East. Immigrants from Ethiopia and Eritrea (a region in northeastern Africa bordering the Red Sea, formerly an Italian colony, later an Ethiopian province, now independent) brought one version of this ritual to the United States, where similar setups can be found in suburban American kitchens or living rooms.

From Brown to Black: A Completely New Way to Drink Coffee

Those paying attention will notice that in Palgrave's description, Arabs roasted coffee beans only to a light brown color level. Early historical records from before approximately 1600 AD indicate that a completely different coffee preparation method developed in Turkey, Syria, and Egypt. They roasted coffee beans to a very dark, nearly black degree, ground them into very fine powder using stone grinders or metal-blade grinders, boiled the powder, added sucrose, and drank it without any spices or filtering. When drinking this sweet coffee, fine coffee powder floating on the surface would also be consumed. Additionally, this beverage was served in smaller cups than those used by Arabs.

The reasons for these differences in roasting patterns, brewing methods, and consumption styles are unclear, but we can deduce that the darker coffee beans are roasted, the easier they are to grind into fine powder. Lighter roasted coffee beans are relatively harder, making fine grinding difficult. Additionally, sucrose from India was widely cultivated on a large scale in the Middle East. This readily available crop became the best tool for suppressing the bitterness of dark-roasted coffee while enhancing its sweetness. Thus, new technological inventions (grinders with metal blades), completely new dark roasting patterns, and the accessibility of sucrose created this entirely new coffee drinking method—Turkish coffee.

Why is it called "Turkish" rather than "Egyptian" or "Syrian"? This is because Europeans first encountered coffee through northern Turkey, then through the Balkan Peninsula and Vienna into central Europe. Early Europeans imitated the Turkish method of drinking coffee, roasting beans very dark, boiling until thick, and adding sucrose.

Coffee Goes Global

From the 17th to early 18th century, coffee drinking habits spread from Europe throughout the entire continent westward and eastward into India and today's Indonesia. As for coffee becoming a cultivated crop, Muslims brought seeds from Yemen to India, then Europeans brought seeds to Ceylon and Java. From Java, seeds were brought to indoor botanical gardens in Amsterdam and Paris, then to the Caribbean and South America as economic crops. Within just a few decades, millions of coffee trees were systematically planted in large quantities on plantations, becoming profitable tools for plantation owners and merchants, as well as sources of inspiration for philosophers and thinkers gathered in coffee houses in London, Paris, Vienna, and elsewhere.

In 17th and 18th-century global trade, coffee was a new commercial economic crop. In the global trade goods of that time, coffee and sucrose were always complementary partners. Both were sister economic crops from tropical regions and very close partners in coffee houses and every cup of coffee worldwide. However, the destructive impact of coffee trees on nature and harvesting workers was far less than that of sucrose. Coffee trees had to grow under the shade of other taller trees, unlike sugarcane which required large-scale field clearing that destroyed original ecosystems. Additionally, individual coffee farmers could earn better incomes, while sugarcane farmers were not so fortunate!

However, coffee brought another universal irony—it became a symbol of both oppression and liberation. In tropical regions, coffee developed into a social and economic profit-making tool, an exceptionally profitable crop. However, it was built on the exploitation of Black labor and also became one of the main catalysts for the European Enlightenment and political revolutions in France and America. At that time, coffee and coffee houses were always inextricably linked to significant cultural and political changes.

Furthermore, in the late 17th and early 18th centuries, Europeans discovered coffee's second important partner—milk. For example, the now beloved latte (Caffe Latte), made with hot milk and espresso, originated in Vienna. In 1683 AD, Vienna was besieged by Turks. When the Turkish army withdrew from Vienna, they left behind some coffee beans, which were used by a man named Franz Kolschitzky to open Vienna's first coffee house. To help Viennese people break their breakfast habit of drinking warm beer, he had to make some changes to the coffee, abandoning the Turkish preparation method and developing a completely new milk-added coffee drinking method.

Vienna changed the Turkish method of drinking coffee with grounds to filtering out the grounds and adding milk. This method quickly spread throughout Europe. By this time, the differentiation in drinking methods became more pronounced: 17th-century Europeans drank Turkish-style coffee with floating grounds and added sucrose; 18th-century Europeans filtered out grounds and added milk. This corresponded to the differences in drinking habits between Ottoman Turkish Empire territories and European Catholic regions. For example: Europeans in Germany or Italy tended toward filtered, milk-added coffee drinking methods; while in the Balkan region (still under Ottoman Turkish rule before the 19th century), most people still preferred the Turkish method of drinking coffee.

Improving Coffee Bean Roasting with Technology

Although coffee drinking methods and cultivation techniques developed dramatically in the 17th and 18th centuries, progress in roasting was unremarkable. The most common roasting method at that time followed the simple Middle Eastern approach: placing green coffee beans in an iron flat pan, then moving it over a fire to roast while continuously stirring until the beans turned brown. There were also some relatively complex devices, such as metal cylinders or hollow spheres that could hold green coffee beans, suspended above a heat source for roasting, equipped with hand-operated stirring mechanisms. These devices could roast several pounds of coffee beans at once and were often used by coffee houses or small roasting retail shops. Smaller versions were available for home use, allowing small quantities of coffee beans to be roasted in residential fireplaces. The illustration below shows such a device and its description, and you can also see examples of this roasting equipment on pages 48-58 of this book.

More Difficult Questions

For example: Where did Europeans and Americans roast coffee beans in the 17th and 18th centuries? Did they roast coffee beans at home or buy roasted beans from shops? How did the coffee taste compared to today's roasting methods?

Of these three questions, only the first two can be answered with available clues: people at that time had coffee beans roasted at home by servants or bought them back from shops. For people at that time, roasting coffee beans was not as difficult as other kitchen tasks. In Europe, this job was usually handled by older children in the family.

So how well did they roast them? How did coffee roasted this way taste? Considering: iron pans, uneven heat, and done by children, it's not difficult to foresee that such roasting quality could not ensure stable results, and burnt coffee beans were often produced. Coffee beans bought from shops might have been more stable at that time, but there weren't many shops that could roast well.

However, it's certain that people drinking coffee they roasted themselves or that was shop-roasted, even if freshly roasted, still performed slightly better than today's instant coffee or cheap canned coffee powder!

The Relationship Between Roasting Patterns and Regions

In past eras, different regions adopted very different roasting depths, similar to modern regional taste preferences. For example, in most of Europe during the 16th and 17th centuries, people drank very dark-roasted Turkish-style coffee. For instance, a 17th-century home roasting advice booklet described: "Take any amount of green coffee beans as you please, throw them into a frying pan, move them over charcoal fire, continuously stir the beans in the pan until the coffee beans approach black color..."

However, there were exceptions. In northern European regions such as Germany, Scandinavia, and Britain, their roasting habits were lighter than other European regions that preferred Turkish-style roasting. This difference was also evident in New World colonies: North American regions ruled by northern European colonial powers mostly preferred lighter roasting patterns, while Latin American regions ruled by southern colonial powers preferred darker roasting patterns.

Another explanation reveals why people in northern Europe abandoned the Turkish deep-roast drinking method and turned to lighter-roasted coffee beans: this taste preference shift occurred around the late 17th to early 18th century when Europeans began adopting new filtering drinking methods. Some believe this taste preference change might be related to northern Europeans' consumption of light-tasting beverages like tea and beer, which also explains why northern Europeans later developed such different approaches to roasting and brewing.

The Arabian Peninsula region and parts of East Africa still maintain traditional drinking methods and use lighter roasting patterns, brewing with spices but without sugar.

The Industrial Revolution Era

In the early 19th century, most Europeans and Americans lived in rural areas working in agriculture. However, by the late 19th century, increasingly more people moved to urban life, with employment shifting to industry and services. In the early 19th century, life was inseparable from closed traditional systems. By 1999 AD, people had broader horizons, with lives closely connected to newspapers and advertisements. The early 19th century had only simple mechanical structures and tools, with most energy coming from renewable water and wind power. By the late 19th century, many complex mechanical devices closely connected to people's lives appeared, with most energy coming from coal and oil.

Coffee beans also changed with this trend: in the early 19th century, whether roasting coffee beans at home or buying roasted beans from stores or coffee houses, the roasting equipment used had relatively simple structures. By the late 19th century, more and more urban residents bought coffee beans roasted in large, complex roasting machines, and these coffee beans even had brand logos.

However, after this point, development levels varied greatly by region. The United States remained at the forefront, using roasted coffee beans or ground coffee powder to replace home coffee roasting activities. Germany and the British Empire followed closely. However, other industrialized countries like France and Italy maintained older, small-scale roasting traditions.

Page 36 of this book contains one of the earliest branded coffee bean advertisements, intended to attract people who roasted coffee beans at home to buy their packaged branded roasted coffee beans. Such advertisements became increasingly frequent as Europeans and Americans moved further away from their hometowns for work. In working-class families, both women and men had to go out to work. By the late 19th century, some wealthier families, who had previously assigned coffee bean roasting tasks to domestic servants, were now forced to do it themselves to enjoy freshly roasted coffee at home. From this advertisement's content, it's easy to see why more and more people were willing to spend a little more money to buy roasted coffee beans—it was simply too convenient!

This new trend of buying fresh bread and roasted coffee beans from shops was also driven by the mysterious force behind the Industrial Revolution of the 19th and early 20th centuries. At that time, buying roasted coffee beans was a clean modern practice, while home coffee roasting was considered dirty, clumsy, messy, outdated, and something only ignorant country folk would do.

Pursuing Quality Stability

With advertising and branding, the next most important step was having stable, reliable products. When a consumer bought these beautifully packaged roasted coffee beans home, they would hope this batch of coffee tasted as good as the batch they bought the previous week. The new type of coffee roasters also focused on quality stability, not only improving the quality control of green coffee beans but also enhancing stability during the roasting stage.

Stabilizing green coffee bean quality required consideration of many factors. As international coffee bean trade developed with specialized terminology and coffee bean classification systems, it became increasingly organized and specialized, making coffee bean trading very convenient. Coffee-producing countries adopted very complex grading standards, and the art of blending began to develop (professionals learned how to perform magic tricks using coffee beans from different harvest seasons and regions, thereby maintaining quality stability while also stabilizing material costs).

At the same time, the American coffee industry developed a set of trading terminology primarily indicating roasting depth and roasting patterns: Cinnamon, Light, Medium, High, City, Full City, Dark, Heavy. Different corporate systems typically fixed on one roasting pattern, making it easier to maintain product stability.

Clumsily Doing Clumsy Things: 19th-Century Roasting Technology

Did technology change society, or did social change drive technological innovation? This question never had a clear answer. However, we can be certain that both have always moved forward together, transforming 19th-century coffee roasting activities from small-scale, private operations to large-scale enterprises using advertising and mass marketing techniques. The stability of roasting patterns for brand-marketed coffee beans could only be achieved through more precise roasting technology.

During the Industrial Revolution, various novel inventions continuously emerged. Some research-oriented companies targeted developing a single machine that could produce every type of coffee drink needed in the 19th century, from roasting to brewing all in one machine. In industrialized countries of that era, patent applications for various new coffee brewers, grinders, and roasters continuously poured into patent offices. Although only a small portion of these patented inventions had significant influence, these patents contributed greatly to the evolution of roasting technology during this period.

During this period, coffee beans were still roasted using cylindrical or spherical roasting equipment, but these devices became increasingly larger, transitioning from small roasters used at home or in small coffee shops to large roasting factories. Page 35 of this book contains an interior view of a mid-19th-century American roasting factory for reference.

The roasting drums of this era were mechanically driven, initially powered by steam, and by the late 19th century, by electricity. The heat source also changed from burning wood and coal to burning natural gas. In the late 19th century, the debate between "direct gas flame roasting" and "indirect gas flame roasting" began. The former allowed gas and flames to directly enter the roasting chamber and contact coffee beans, while the latter prevented gas and flames from directly entering the roasting chamber, instead heating the roasting chamber with flames, with hot air then indirectly entering the roasting chamber through blowers.

Two Deeper Technological Innovations: (1) Precise Temperature/Time Control; (2) Uniform Roasting, Ensuring Consistent Roast for Every Bean

First, let's look at the innovation regarding time control. As roasting drums and roasting spheres became larger and batch roasting quantities increased, cooling coffee beans became increasingly difficult because even after leaving the roasting environment, the beans still contained internal heat and could continue roasting (this phenomenon is called "self-roasting" or "after-roasting").

In the early 19th century, the solution to achieving more stable coffee bean roasting focused on "removing coffee beans from the roasting chamber more quickly and easily." For example, the "Carter Pull-Out Roaster" on page 35 was designed with this concept in mind. Its selling point was that the roasting drum could be quickly pulled away from the furnace fire, and the coffee beans inside could be easily poured out. However, as can be observed from the illustration, the poured coffee beans still required manual stirring to accelerate cooling. Both methods could effectively reduce the surface temperature of coffee beans while carrying away the smoke released by freshly roasted coffee beans.

Another innovation in the late 19th century addressed the technical challenge of "how to make roasting more uniform." Most early 19th-century roasting drums or spherical roasters were simple hollow roasting chambers where coffee beans would cluster together, making "position changing" difficult. Therefore, beans originally at the bottom would continuously receive heat and eventually burn, while beans at the top had difficulty receiving heat. Additionally, oils released from coffee beans during roasting would form an oily film on the inner surface of the roasting chamber, often sticking the beans to certain positions in the metal roasting chamber.

Also in the mid-19th century, stirring blades or stirring paddles were added to roasting chambers, improving roasting uniformity. By 1864 AD, Jabez Burns, a renowned American roasting technology leader, solved the "bean dropping" problem (the term "bean dropping" refers to the process of pouring out and cooling coffee beans after roasting completion). The company designed two sets of spiral blade groups fixed inside the roasting chamber, allowing coffee beans to move up and down within the chamber during roasting. After roasting completion, the operator only needed to open the roasting chamber's opening, and the coffee beans inside would automatically be pushed out into the cooling tray.

However, by the late 19th century, more efficient methods for improving roasting uniformity emerged. To assist heating uniformity, besides direct heat sources applied to the roasting chamber surface, fans or blowers were used to send hot air into the roasting chamber. This hot air served to appropriately cool the coffee beans (here "appropriately cooling coffee beans" doesn't mean rapidly lowering the internal bean temperature, but rather using convection principles to prevent coffee beans in the roasting drum from smoldering, avoiding sudden temperature increases). During roasting, coffee beans were continuously stirred by blades, and hot air flow continuously circulated within the roasting chamber, meaning coffee beans contacted hot air more frequently than the metal walls of the roasting chamber. This design improved roasting stability and batch roasting speed. Additionally, for the heating part, the original design that only heated below the roasting drum was changed to ensure uniform heating around the entire roasting drum. This design transformed the original single-layer roasting drum wall into inner and outer double-layer walls, circulating the heated air from outside the drum between the two wall layers.

Overall, Typical Drum Roasters Must Include the Following Basic Components:

1. Uniformly conducted gas flame heat source.

2. Precise and rapid bean dropping design.

3. Blade design inside the roasting drum.

4. Blowers that draw heated airflow into the roasting chamber to stabilize temperature increase.

5. Cooling fans that blow room-temperature air from beneath the cooling tray.

These basic components remain the main functional devices of most small drum roasters today. You can see related roaster illustrations and descriptions on pages 60-61.

Of course, besides this basic structure, there are many other versions of basic component structures. Some turn-of-the-century roasters even moved the gas flame source inside the roasting drum. Most modern large-scale system roasting equipment is equipped with a water mist cooling device to rapidly cool large quantities of roasted coffee beans. This cooling method is called "Water Quenching" and is another effective cooling method besides the "Air Quenching" method described earlier in this book.

Despite so many changes over these decades, some roaster constructions have remained unchanged for decades, and old-style roaster mechanisms are still used today in places like Japan, Brazil, and certain parts of the United States. Customers in these regions particularly appreciate the smoky, carbon-burning aroma layers produced by the slow-fire roasting of these roasters.

However, today's drum roasters still predominantly use indirect heating designs with blowers introducing hot air, except for the largest roasting factories which do not use this roaster structure.

Traditional Roasters: Relying on Noses and Eyes

Hand-cranked stirring roasting devices have always been the mainstream of small-scale roasting. The structure of these roasting devices is essentially the same as the Neapolitan hand-cranked drum roaster described by Edouard Philippe in Chapter 1.

Traditional roasters rely on visual observation (watching changes in coffee bean color), hearing (the cracking sounds of coffee beans), and smell (different roasting odors produced at different roasting stages) during roasting. They use a device called a "Trier" to check the color degree of roasting coffee beans. Usually, a hole is made at the front of the roaster's drum to place the trier. By judging the appearance color of the sampled coffee beans, they decide when to stop roasting. The color judgment process must be conducted under fixed light sources, and the roaster must have sufficient experience. Adjusting roasting chamber temperature is also a task that relies on experience, requiring finding a general roasting pattern and making roasting adjustments for specific flavor defects of certain coffee bean varieties.

For traditional roasters, they always hold a conservative view of coffee roasting, believing it's an art that must be learned through experience, with this art becoming increasingly refined through memory blocks and various sensory perceptions.

Science Quietly Integrates into Art

Gradually, what was once considered most important—the "artistic sense" and "sensory judgment"—has been replaced by "science" and "tools." In other words, the "memory" that people previously relied on for roasting has gradually been replaced by objective, collective "data" and "chart information."

The evolution of roasting described above was made possible by the invention of many tools and control instruments. The first was a simple device that could measure approximate internal coffee bean temperature, usually called "Thermocouples" or "Heat probe." This is an electronic thermometer whose sensing tip can be placed inside the roasting chamber, buried in the continuously rolling pile of coffee beans. Although the air temperature in the roasting chamber differs from the coffee bean temperature, the coffee bean pile seems to completely isolate the chamber's air temperature, so the temperature measured by the probe is not affected by the chamber's air temperature. The approximate coffee bean pile temperature value is transmitted to a display outside the roaster.

Once the chemical reactions in coffee beans begin (that is, "pyrolysis," or first crack), the measured coffee bean pile temperature becomes increasingly valuable, allowing roasters to clearly determine the current roasting depth. You can imagine this scene: when a turkey is almost perfectly roasted, a small thermometer inserted into the muscle pops up. Similarly, our measured coffee bean pile temperature can reveal how far the coffee beans' roasting degree has progressed. Therefore, thermometers can replace human eyes, allowing roasters to decide when to drop beans based on "temperature" rather than "visually observed color degree," or adjust roasting chamber temperature according to read temperature values. You can also refer to the approximate "coffee bean roasting temperature/roasting depth" correspondence chart on pages 80-81 of this book. On these latest roasters, there are even tools that can automatically trigger the cooling process when coffee beans reach a set roasting temperature.

The second important control instrument combines roasting chamber internal temperature monitoring with heat source supply, automatically monitoring heat supply to maintain the chamber temperature consistently at predicted values. This invention is very practical because when coffee beans reach the pyrolysis stage, they begin to emit heat energy themselves. If external heat source maintains its original intensity, the heat energy released by coffee beans can cause the chamber temperature to rise instantly, sometimes quickly reaching the bean dropping temperature point. According to roasting experience, this uncontrollable sudden temperature increase can lead to premature reaching of the dropping temperature point, burning too many aromatic substances, and causing deterioration of coffee bean structure.

The third instrument is the "Near-Infrared Spectrophotometer," collectively called "Agtron," named after its inventor and company. It can measure certain wavelength colors or electromagnetic waves invisible to the human eye, which correspond very precisely to coffee bean roasting depth. Additionally, this instrument is not affected by light brightness or human factors (like being distracted by talkative people affecting mood). The "Near-Infrared Spectrophotometer" can not only accurately and stably measure the energy of this narrow frequency band but also convert measured energy into reference data. Thus, even two roasters far apart can compare differences in their roasting processes through data read by this instrument.

Long-standing understanding of coffee beans tells us: denser/higher moisture content coffee beans require longer time to reach a default roasting pattern, while lighter/drier coffee beans require relatively shorter time. Today's technological development has combined roasters with precision instruments that can read coffee bean density. Based on coffee bean density data obtained from this numerical system, roasting chamber temperature and other variables are set before roasting. Traditional coffee bean machines can only make adjustments based on the roaster's past experience with specific coffee beans.

The final development is the control of convective hot air/gas flow in the roasting chamber, which some latest roasting equipment can control very precisely. Traditional drum roasters have always been able to adjust the air flow in the roasting chamber through "Damper" control, similar to adjusting fireplace convection in European and American homes, but traditional roasters still only roughly control this variable, not precise quantifiable control.

Therefore, Today's Systematic Roasters Have Four to Five Quantifiable Variables for Roasters to Control:

1. The coffee beans' own moisture content and density.

2. Roasting chamber temperature.

3. Coffee bean pile temperature.

4. Precisely measured roasted bean color degree (Agtron).

5. Flow control of convective hot air in the roasting chamber (only some models have this control).

Considering more detailed environmental variables like external room temperature, altitude, atmospheric pressure, roasting curve charts drawn from these four to five quantifiable variables, as well as the coffee bean roasting process and bean dropping timing are recorded using objective measurement data, replacing the empirical recording methods of ears, nose, and eyes. With the increasing prevalence of computer applications, roasters can easily change temperature and other variables in the roasting chamber to create other combinations of roasting patterns. In terms of roasting time adjustment, time can be increased or decreased by the second, allowing for more precise adjustment of subtle taste differences. This evolution is called "Profile Roasting." Using profile roasting, old beans or hollow-tasting coffee beans might gain some complexity; while coffee beans with rough edges or higher acidity can become milder and sweeter.

Taste is Supreme: The Verdict Comes After Tasting

Perhaps you've patiently followed each step mentioned above, or perhaps you've completely skipped ahead to direct operation. Regardless of which approach you've taken, you'll find that the application of these instruments can transform previous roasting methods that relied entirely on the roaster's intuitive system (memory and sensory nerve transmission) into more complex yet more precise data-driven roasting.

However, the only sensory organ that cannot be replaced by instruments is taste. Even when we use completely systematic data-driven roasting, the roaster (traditionally called Roaster, now increasingly called Roastmaster) must still taste each batch of coffee after completing it, adjusting previous roasting data according to personal preferences and roasting principles. From here on, various coffee flavors created by different roasting curves will continue to bring us taste surprises while also enriching coffee's cultural connotation and appreciation value. And "roasting" itself may continue to develop in parallel with technology in the form of "art."

Recommended Coffee Bean Brands for Beginners

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Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473