Coffee roasting - AbsoluteAstronomy.com

Roasting coffee transforms the chemical and physical properties of green coffee beans

Coffee processing

Processing of coffee is the method converting the raw fruit of the coffee plant into the coffee. The cherry has the fruit or pulp removed leaving the seed or bean which is then dried...

into roasted coffee

Coffee

Coffee is a brewed beverage with a dark,init brooo acidic flavor prepared from the roasted seeds of the coffee plant, colloquially called coffee beans. The beans are found in coffee cherries, which grow on trees cultivated in over 70 countries, primarily in equatorial Latin America, Southeast Asia,...

products. The roasting process is what produces the characteristic flavor of coffee by causing the green coffee beans to expand and to change in color, taste, smell, and density. Unroasted beans contain similar acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

s, protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

, and caffeine

Caffeine

Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...

as those that have been roasted, but lack the taste. Heat must be applied for the Maillard

Maillard reaction

The Maillard reaction is a form of nonenzymatic browning similar to caramelization. It results from a chemical reaction between an amino acid and a reducing sugar, usually requiring heat....

and other chemical reactions to occur.

As green coffee is more stable than roasted, the roasting process tends to take place close to where it will be consumed. This reduces the time that roasted coffee spends in distribution, giving the consumer a longer shelf life. The vast majority of coffee is roasted commercially on a large scale, but some coffee drinkers roast coffee at home

Home roasting coffee

Home roasting is the process of roasting coffee from green coffee beans on a small scale for personal consumption. Home roasting of coffee has been practiced for centuries, and has utilized numerous methods of roasting the beans such as roasting in pans over a fire and hand turning iron drums on a...

in order to have more control over the freshness and flavor profile of the beans.

Process

The coffee roasting process follows coffee processing

Coffee processing

Processing of coffee is the method converting the raw fruit of the coffee plant into the coffee. The cherry has the fruit or pulp removed leaving the seed or bean which is then dried...

and precedes coffee brewing. It consists essentially of sorting, roasting, cooling, and packaging 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 240–275 °C (464–527 °F), and the beans are roasted for a period of time ranging from 3 to 30 minutes. Initially, the process is endothermic

Endothermic

In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...

(absorbing heat), but at around 175 °C (347 °F) it becomes exothermic

Exothermic

In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

(giving off heat). 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 cooled with forced air. Sometimes, in large commercial roasters, the beans are first quenched with a fine water mist. Torrefacto

Torrefacto

Torrefacto refers to a particular process of roasting coffee beans, common in Spain, France, Portugal, Costa Rica and Argentina. The process involves adding a certain amount of sugar during roasting in order to glaze the beans. This results in a reduction in the acidity and bitter taste of the coffee...

is a roasting process used in Spain and parts of Latin America involving the addition of sugar.

Equipment

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.

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.

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

Fluidized bed

A fluidized bed is formed when a quantity of a solid particulate substance is placed under appropriate conditions to cause the solid/fluid mixture to behave as a fluid. This is usually achieved by the introduction of pressurized fluid through the particulate medium...

Degree of roast

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. Roastmasters 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, variety, 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.

Determining degree of roast

The most popular, but probably the least accurate, method of determining the degree of roast is to judge the bean's color by eye (the exception to this is using a colorimeter to measure the ground coffee reflectance under infrared light and comparing it to standards such as the Agtron scale). As the beans absorb 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. Beans will also darken as they age, making color alone a poor roast determinant. Most roasters use a combination of bean mass temperature, smell, color, and sound to monitor the roasting process.

Sound is a good indicator of bean temperature during roasting. There are two temperature thresholds called "cracks" that roasters listen for. At about 205–207 °C (401–404.6 °F), beans will emit a cracking sound much like popcorn does when it pops, only much quieter. This point is called "first crack," marking the beginning of light roasts. When the beans are at about 224–227 °C (435.2–440.6 °F), or a medium roast, they emit a "second crack." This is the dividing point between medium and dark roasts.

Degree of roast pictorial

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.

	22 °C (71.6 °F) Green Beans Green coffee beans as they arrive at the dock. They can be stored for up to two years.		165 °C (329 °F) Drying Phase As beans roast, they lose water and increase in size. Arabic coffee is prepared using this roast.
	195 °C (383 °F) Cinnamon Roast The lightest drinkable roast, immediately before first crack. Light brown, toasted grain flavors with sharp acidic tones.		205 °C (401 °F) New England Roast Moderate light brown, still acidic but not bready, a traditional roast for Northeastern U.S. Coffee, at first crack.
	210 °C (410 °F) American Roast Medium light brown, the traditional roast for the Eastern U.S. First crack ending.		220 °C (428 °F) City Roast Medium brown, the norm for most of the U.S., good for tasting the varietal character of a bean.
	225 °C (437 °F) Full City Roast Medium dark brown with occasional oil sheen, good for varietal character and bittersweet flavors. At the beginning of second crack.		230 °C (446 °F) Vienna Roast Moderate dark brown with light surface oil, more bittersweet, caramel-y flavor, acidity muted. In the middle of second crack. Occasionally used for espresso blends.
	240 °C (464 °F) French Roast Dark brown, shiny with oil, burnt undertones, acidity diminished. At the end of second crack. A popular roast for espresso blends.		245 °C (473 °F) Italian Roast Very dark brown and shiny, burnt tones become more distinct, acidity almost gone, thin body. The common roast for espresso blends.
	250 °C (482 °F) Spanish Roast Extremely dark brown, nearly black and very shiny, charcoal and tar tones dominate, flat, with thin body.

Caffeine content by roast level

Caffeine content varies by roast level. Caffeine diminishes with increased roasting level: light roast, 1.37%; medium roast, 1.31%; and dark roast, 1.31%. However, this does not remain constant in coffee brewed from different grinds and brewing methods.

Roast naming confusions

There is no such thing as an "espresso roast." Espresso is a beverage, not a temperature. Blends of beans intended for espresso are generally roasted from between Full City and Italian roast. In recent years, the term French Roast has been marketed as the name for a coffee blend or style. While appropriately roasted to French roast, it blurs the line between blend name and temperature.

Roast flavors

At lighter roasts, the bean will exhibit more of its "origin flavor"; the flavors created in the bean by its variety, the soil, altitude, and weather conditions in the location where it was grown.

Coffee beans from famous regions like Java

Java coffee

Java coffee is a coffee produced on the island of Java. In the United States the term "Java" by itself is, in general, slang for coffee. The Indonesian phrase Kopi Jawa refers not only to the origin of the coffee, but is used to distinguish the strong, black, very sweet coffee, with powdered grains...

, Kenya

Coffee Industry of Kenya

The coffee industry of Kenya is noted for its cooperative system of production, processing, milling, marketing, and auctioning coffee. About 70% of Kenyan coffee is produced by small scale holders. It is estimated that six-million Kenyans are employed directly or indirectly in the coffee industry....

, Hawaiian Kona

Kona coffee

Kona coffee is the market name for coffee cultivated on the slopes of Hualalai and Mauna Loa in the North and South Kona Districts of the Big Island of Hawaii. It is one of the most expensive coffees in the world. Only coffee from the Kona Districts can be described as "Kona"...

, and Jamaican Blue Mountain

Jamaican Blue Mountain Coffee

Jamaican Blue Mountain Coffee or Jamaica Blue Mountain Coffee is a classification of coffee grown in the Blue Mountains of Jamaica. The best lots of Blue Mountain coffee are noted for their mild flavour and lack of bitterness...

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

Qualitative research

Qualitative research is a method of inquiry employed in many different academic disciplines, traditionally in the social sciences, but also in market research and further contexts. Qualitative researchers aim to gather an in-depth understanding of human behavior and the reasons that govern such...

, and thus subjective

Subjectivity

Subjectivity refers to the subject and his or her perspective, feelings, beliefs, and desires. In philosophy, the term is usually contrasted with objectivity.-Qualia:...

. As a rule of thumb

Rule of thumb

A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...

, 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 “pop” 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. Smoother than the traditional American "medium" roast, but may display fewer of the distinctive taste characteristics of the original coffee.
Full Roast	High, Viennese, 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.

Home roasting

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. 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.

Packaging

Extending the shelflife 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 2 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

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

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. Refrigeration and freezing retards the staling process. Roasted whole beans can be considered fresh for up to one month if kept cool. Once coffee is ground it is best used immediately.

Emissions and control

Particulate matter (PM), volatile organic compound

Volatile organic compound

Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and...

s (VOC), organic acid

Organic acid

An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are relatively stronger acids. The relative stability of the conjugate...

s, 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 pollutant

Pollutant

A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...

s, including alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s, aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

s, organic acid

Organic acid

s, and nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

and sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

compounds. Because roasters are typically natural gas-fired, carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

(CO) and carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

(CO₂) emissions result from fuel combustion. Decaffeination

Decaffeination

Decaffeination is the act of removing caffeine from coffee beans, cocoa, tea leaves and other caffeine-containing materials. Despite removal of caffeine, many decaffeinated drinks still have around 1-2% of the...

and instant coffee

Instant coffee

Instant coffee, also called soluble coffee and coffee powder, is a beverage derived from brewed coffee beans. Instant coffee is commercially prepared by either freeze-drying or spray drying, after which it can be rehydrated...

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 cyclone

Cyclonic separation

Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids...

s 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

Operating temperature

An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...

is typically between 650–816 °C (1,202–1,500.8 °F), which is 93–260 °C (199.4–500 °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 dryer

Spray drying

Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some...

s are typically controlled by a cyclone followed by a wet scrubber

Wet scrubber

The term wet scrubber describes a variety of devices that remove pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by...

External links

Homeroasters.org

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