Coffee bean

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The appearance of unroasted, green coffee beans.
Roasted coffee beans.

A coffee bean is a seed of the coffee plant, and is the source for coffee. It is the pit inside the red or purple fruit often referred to as a cherry. Even though they are seeds, they are referred to as 'beans' because of their resemblance to true beans. The fruits - coffee cherries or coffee berries - most commonly contain two stones with their flat sides together. A small percentage of cherries contain a single seed, instead of the usual two. This is called a "peaberry." The peaberry is more unusual occurring only between 10 and 15 percent of the time, and it's a fairly common (yet scientifically unproven) belief that they have more flavour than 'normal' coffee beans.[1] Like Brazil nuts (a seed) and white rice, coffee beans consist mostly of endosperm.[2]

The two most economically important varieties of coffee plant are the Arabica and the Robusta; 75-80% of the coffee produced worldwide is Arabica and 20% is Robusta.[2] Arabica beans consist of 0.8-1.4% caffeine and Robusta beans consist of 1.7-4% caffeine.[3] As coffee is one of the world's most widely consumed beverages, coffee beans are a major cash crop, and an important export product, counting for over 50% of some developing nations' foreign exchange earnings.[4]

Origin and distribution[edit]

Coffee berries

The plants were first introduced in the Americas around 1723.

South America is now responsible for approximately 45% of the world's total coffee exports. Most of this coffee is grown in Brazil.[5]

The United States imports more coffee than any other nation.[5] The per capita consumption of coffee in the United States in 2011 was 4.24 kg (9 lbs), and the value of coffee imported exceeded $8 billion.[6]

Significant dates[edit]

  • First coffee plant was found in the mountains of Yemen. Then by 1500 it was exported to the rest of the world through the port of Mokha in Yemen.
  • First cultivation in India (Mysore) - 1600
  • First cultivation in Europe (also first cultivation outside of east Africa/Arabia) - 1616
  • First cultivation in Java - 1699
  • First cultivation in Caribbean (Cuba, Hispaniola (Haiti and the Dominican Republic), Jamaica, Puerto Rico) – 1715–1730
  • First cultivation in South America – 1730
  • First cultivation in Dutch East Indies – 1720
  • Roasted beans first sold on retail market (Pittsburgh) – 1865
  • Important spray-drying techniques developed in 1950s

Etymology[edit]

The Oxford English Dictionary suggests that the European languages generally appear to have got the name from Turkish kahveh, about 1600, perhaps through Italian caffè. Arab qahwah, in Turkish pronounced kahveh, the name of the infusion or beverage; said by Arab lexicographers to have originally meant ‘wine’ or some type of wine, and to be a derivative of a verb-root qahiya ‘to have no appetite.’ Another common theory is that the name derives from Kaffa Province, Ethiopia, where the species may possibly have originated.[7]

Coffee plant[edit]

The coffee tree averages from 5–10 m (16–33 ft) in height. As the tree gets older, it branches less and less and bears more leaves and fruit.

Coffee plants are grown in rows several feet apart. Some farmers plant fruit trees around them or plant the coffee on the sides of hills, because they need specific conditions to flourish. Ideally, Arabica coffee beans are grown at temperatures between 15–24 °C (59–75 °F) and Robusta at 24–30 °C (75–86 °F) and receive between 15–30 cm (5.9–11.8 in) of rainfall per year.[8] Heavy rain is needed in the beginning of the season when the fruit is developing, and less later in the season as it ripens.

Processing[edit]

For more details on this topic, see Processing of coffee.

When the fruit is ripe, it is almost always handpicked, using either "selective picking", where only the ripe fruit is removed, or "strip-picking", where all of the fruit is removed from a branch all at once. This also gives the growers reason to give their blend of origin a certain Spec called OCR (operation Cherry red). In rare circumstances, the Asian Palm Civet will eat a coffee berry and excrete the beans. These beans are called Kopi Luwak, and can be processed further into a rare and expensive coffee.

There are two methods of processing the coffee berries. The first method is "wet processing", which is usually carried out in Central America and areas of Africa. The flesh of the berries is separated from the seeds and then the seeds are fermented – soaked in water for about two days. This dissolves any pulp or sticky residue that may still be attached to the seeds.

The "dry processing" method is cheaper and simpler, used for lower quality beans in Brazil and much of Africa. Twigs and other foreign objects are separated from the berries and the fruit is then spread out in the sun on concrete or brick for 2–3 weeks, turned regularly for even drying.

Composition[edit]

The term “green coffee bean” refers to unroasted mature or immature coffee beans. These have been processed by wet or dry methods for removing the outer pulp and mucilage, and have an intact wax layer on the outer surface. When immature, they are green. When mature, they have a brown to yellow or reddish color, and typically weigh 300 to 330 mg per dried coffee bean. Nonvolatile and volatile compounds in green coffee beans, such as caffeine, deter many insects and animals from eating them. Further, both nonvolatile and volatile compounds contribute to the flavor of the coffee bean when it is roasted. Nonvolatile nitrogenous compounds (including alkaloids, trigonelline, proteins and free amino acids) and carbohydrates are of major importance in producing the full aroma of roasted coffee, and for its biological action. Since the mid 2000s green coffee extract has been sold as a nutritional supplement, and has been clinically studied for its chlorogenic acid content and for its lipolytic and weight-loss properties.

Nonvolatile alkaloids[edit]

Immature Coffea canephora berries on a tree in Goa, India.

Caffeine (1,3,7-trimethyl-xanthine) is the alkaloid most present in green and roasted coffee beans. The content of caffeine is between 1.0% and 2.5% by weight of dry green coffee beans. The content of caffeine does not change during maturation of green coffee beans.[9] Lower concentrations of theophylline, theobromine, paraxanthine, liberine, and methylliberine can be found. The concentration of theophylline, an alkaloid noted for its presence in green tea, is reduced during the roasting process, usually about 15 minutes at 230 °C (446 °F), whereas the concentration of most other alkaloids are not changed.[10] The solubility of caffeine in water increases with temperature and with the addition of chlorogenic acids, citric acid, or tartaric acid, all of which are present in green coffee beans. For example, 1 g (0.035 oz) caffeine dissolves in 46 ml (1.6 US fl oz) of water at room temperature, and 5.5 ml (0.19 US fl oz) at 80 °C (176 °F).[11] The xanthine alkaloids are odorless, but have a bitter taste in water, which is masked by organic acids present in green coffee, however.

Trigonelline (N-methyl-nicotinate) is a derivative of vitamin B6 that is not as bitter as caffeine. In green coffee beans, the content is between 0.6% and 1.0%. At a roasting temperature of 230 °C (446 °F), 85% of the trigonelline is degraded to nicotinic acid, leaving small amounts of the unchanged molecule in the roasted beans. In green coffee beans, trigonelline is synthesized from nicotinic acid (pyridinium-3-carboxylic acid) by methylation from methionine, a sulfur-containing amino acid.[12] Mutagenic activity of trigonelline has been reported.[13]

Proteins and amino acids[edit]

Proteins account for 8% to 12% of dried green coffee beans. A majority of the proteins are of the of 11-S-storage kind [14] (alpha - component of 32 kDa, beta – component of 22 kDa), most of which are degraded to free amino acids during maturation of green coffee beans. Further, 11-S-storage proteins are degraded to their individual amino acids under roasting temperature and are thus an additional source of bitter components due to generation of Maillard reaction products.[15] High temperature, oxygen concentration and low pH degrade 11-S-storage proteins of green coffee beans to low molecular weight peptides and amino acids. The degradation is accelerated in the presence of organic acids such as chlorogenic acids and their derivatives. Other proteins include enzymes, such as catalase and polyphenol oxidase, which are important for the maturation of green coffee beans. Mature coffee contains free amino acids (4.0 mg amino acid/g robusta coffee and up to 4.5 mg amino acid/g arabica coffee). In Coffea arabica, alanine is the amino acid with the highest concentration, i.e. 1.2 mg/g, followed by asparagine of 0.66 mg/g, whereas in C. robusta, alanine is present at a concentration of 0.8 mg/g and asparagine at 0.36 mg/g.[16][17] The free hydrophobic amino acids in fresh green coffee beans contribute to the unpleasant taste, making it impossible to prepare a desirable beverage with such compounds. In fresh green coffee from Peru, these concentrations have been determined as follows: isoleucine 81 mg/kg, leucine 100 mg/kg, valine 93 mg/kg, tyrosine 81 mg/kg, phenylalanine 133 mg/kg. The concentration of gamma-aminobutyric acid (a neurotransmitter) has been determined between 143 mg/kg and 703 mg/kg in green coffee beans from Tanzania.[18] Roasted coffee beans do not contain any free amino acids, the amino acids in green coffee beans are degraded under roasting temperature to Maillard products (reaction products between the aldehyde group of sugar and the alpha-amino-group of the amino acids). Further, diketopiperazines, e.g. cyclo(proline-proline), cyclo(proline-leucine), and cyclo(proline-isoleucine), are generated from the corresponding amino acids, and are the major source of the bitter taste of roasted coffee.[19] The bitter flavor of diketopiperazines is perceptible at around 20 mg/liter of water. The content of diketopiperazines in espresso is about 20 mg to 30 mg, which is responsible for its bitterness.

Carbohydrates[edit]

Carbohydrates make up about 50% of the dry weight of green coffee beans. The carbohydrate fraction of green coffee is dominated by polysaccharides, such as arabinogalactan, galactomannan and cellulose, contributing to the tasteless flavor of green coffee. Arabinogalactan makes up to 17% of dry weight of green coffee beans, with a molecular weight of 90 kDa to 200 kDa. It is composed of beta-1-3-linked galactan main chains, with frequent members of arabinose (pentose) and galactose (hexose) residues at the side chains comprising immunomodulating properties by stimulating the cellular defense system (Th-1 response) of the body. Mature brown to yellow coffee beans contain fewer residues of galactose and arabinose at the side chain of the polysaccharides, making the green coffee bean more resistant to physical breakdown and less soluble in water.[20] The molecular weight of the arabiniogalactan in coffee is higher than in most other plants, improving the cellular defense system of the digestive tract compared to arabinogalactan with lower molecular weight.[21] Free monosaccharides are present in mature brown to yellow-green coffee beans. The free part of monosaccharides contains sucrose (gluco-fructose) up to 9000 mg/100g of arabica green coffee bean, a lower amount in robustas, i.e. 4500 mg/100g. In arabica green coffee beans, the content of free glucose was 30 to 38 mg/100g, free fructose 23 to 30 mg/100g; free galactose 35 mg/100g and mannitol 50 mg/100g dried coffee beans, respectively. Mannitol is a powerful scavenger for hydroxyl radicals, which are generated during the peroxidation of lipids in biological membranes.[22]

Lipids[edit]

The lipids found in green coffee include: linoleic acid, palmitic acid, oleic acid, stearic acid, arachidic acid, diterpenes, triglycerides, unsaturated long-chain fatty acids, esters and amides. The total content of lipids in dried green coffee is between 11.7 g and 14 g / 100 g.[23] Lipids are present on the surface and in the interior matrix of green coffee beans. On the surface, they include derivatives of carboxylic acid-5-hydroxytryptamides with an amide bond to fatty acids (unsaturated C6 to C24) making up to 3% of total lipid content or 1200 to 1400 microgram/g dried green coffee bean. Such compounds form a wax-like cover on the surface of the coffee bean (200 to 300 mg lipids/100 g dried green coffee bean) protecting the interior matrix against oxidation and insects. Further, such molecules have antioxidative activity due to their chemical structure.[24] Lipids of the interior tissue are triglycerides, linoleic acid (46% of total free lipids), palmitic acid (30% to 35% of total free lipids), and esters. Arabica beans have a higher content of lipids (13.5 to 17.4 g lipids/100 g dried green coffee beans) than robustas (9.8 to 10.7 g lipids/100 g dried green coffee beans). The content of diterpenes is about 20% of the lipid fraction. The diterpenes found in green coffee include cafestol, kahweol, 16-O-methylcafestol, cafestal and kahweal. Some of these diterpenes have been shown in in vitro experiments to protect liver tissue against chemical oxidation.[25] In coffee oil from green coffee beans the diterpenes are esterified with saturated long chain fatty acids.

Nonvolatile chlorogenic acids[edit]

Chlorogenic acids belong to a group of compounds known as phenolic acids, which are antioxidants. The content of chlorogenic acids in dried green coffee beans of robusta is 65 mg/g and of arabica 140 mg/g, depending on the timing of harvesting. At roasting temperature, more than 70% of chlorogenic acids are destroyed, leaving a residue of less than 30 mg/g in the roasted coffee bean. In contrast to green coffee, green tea contains an average of 85 mg/g polyphenols. These chlorogenic acids could be a valuable, inexpensive source of antioxidants. Chlorogenic acids are homologous compounds comprising caffeic acid, ferulic acid and 3,4-dimethoxycinnamic acid, which are connected by an ester bond to the hydroxyl groups of quinic acid.[26] The antioxidant capacity of chlorogenic acid is more potent than of ascorbic acid (vitamin C) or mannitol, which is a selective hydroxy-radical scavenger.[27] Chlorogenic acids have a bitter taste in low concentrations such as 50 mg/L water. At higher concentrations of 1 g/L water, they have a sour taste. Chlorogenic acids increase the solubility of caffeine and are important modulators of taste.

Volatile compounds[edit]

Volatile compounds of green coffee beans include short chain fatty acids, aldehydes, and nitrogen-containing aromatic molecules, such as derivatives of pyrazines (green-herbeaceous-earthy odor). Briefly, such volatile compounds are responsible for the unpleasant odor and taste of green coffee, and are capable of causing nausea and vomiting upon inhaling of the odor of ground green coffee beans or ingestion of a beverage made by pulverised green coffee beans. Due to this nauseating odor, green coffee beans have never been used by themselves for the preparation of a refreshing beverage; such a beverage would cause vomiting, although green coffee beans contain the same amount of caffeine as roasted coffee. When green coffee beans are roasted, other molecules with the typical pleasant aroma of coffee are generated, which are not present in fresh green coffee. During roasting, the major part of the unpleasant tasting volatile compounds are neutralised. Unfortunately, other important molecules such as antioxidants and vitamins present in green coffee are destroyed. Volatile compounds with nauseating odor for humans have been identified, including acetic acid (pungent, unpleasant odor), propionic acid (odor of sour milk, or butter), butanoic acid (odor of rancid butter, present in green coffee with 2 mg/100 g coffee beans), pentanoic acid (unpleasant fruity flavor, present in green coffee at 40 mg/100 g in coffee beans), hexanoic acid (fatty-rancid odor), heptanoic acid (fatty odor), octanoic acid (repulsive oily rancid odor); nonanoic acid (mild nut-like fatty odor); decanoic acid (sour repulsive odor), and derivatives of such fatty acids - 3-methyl-valeric acid (sour, green-herbaceous, unpleasant odor), acetaldehyde (pungent-nauseating odor, even when highly diluted, present in dried green coffee beans at concentrations of about 5 mg/kg), propanal (choking effect on respiratory system, penetrating-nauseating), butanal (nauseating effect, present in dried green coffee beans at 2 to 7 mg/kg), or pentanal (very repulsive nauseating effect).[28]

See also[edit]

References[edit]

  1. ^ http://www.hypecoffee.com/content/what-is-a-peaberry
  2. ^ a b "Arabica and Robusta Coffee Plant". Coffee Research Institute. Retrieved 25 August 2011. 
  3. ^ "Botanical Aspects". International Coffee Organization. Retrieved 25 August 2011. 
  4. ^ "The Story of Coffee". International Coffee Organization. Retrieved 25 August 2011. 
  5. ^ a b "Monthly Coffee Market Report" (PDF). International Coffee Organization. July 2011. p. 7. Retrieved 24 August 2011. 
  6. ^ "United States of America Country Datasheet" (PDF). International Coffee Organization. 2011. Retrieved 24 August 2013. 
  7. ^ Richard M. Souza, 2008, Plant-Parasitic Nematodes of Coffee, p. 3.
  8. ^ "Ecology". International Coffee Organization. Retrieved 25 August 2011. 
  9. ^ Clifford, MN, and Kazi, M (1987). "The influence of coffee bean maturity on the content of chlorogenic acids, caffeine, and trigonelline". Food Chemistry 26: 59–69. doi:10.1016/0308-8146(87)90167-1. 
  10. ^ WEIDNER, M, and MAIER, HG; 1999, Seltene Purinalkaloide in Roestkaffee, Lebensmittelchemie, Vol 53, 3, p.58
  11. ^ The Merck Index, 13th Edition
  12. ^ POISSON, J, 1979, Aspects chimiques et biologiquesde la composition du café vert; 8th International Colloquium Chemicum Coffee, Abidjan, 28. Nov to 3. December 1988, published by ASIC 1979, p 33-37; http://www.asic-cafe.org
  13. ^ Wu X, Skog K, Jägerstad M (July 1997). "Trigonelline, a naturally occurring constituent of green coffee beans behind the mutagenic activity of roasted coffee?". Mutat. Res. 391 (3): 171–7. doi:10.1016/s1383-5718(97)00065-x. PMID 9268042. 
  14. ^ "Revista Brasileira de Fisiologia Vegetal - Seed storage proteins in coffee". Scielo.br. Retrieved 2013-12-08. 
  15. ^ Montavon P, Duruz E, Rumo G, Pratz G (April 2003). "Evolution of green coffee protein profiles with maturation and relationship to coffee cup quality". J. Agric. Food Chem. 51 (8): 2328–34. doi:10.1021/jf020831j. PMID 12670177. 
  16. ^ Arnold, U.; Ludwig, E.; Kühn, R.; Möschwitzer, U. (1994). "Analysis of free amino acids in green coffee beans". Zeitschrift für Lebensmittel-Untersuchung und Forschung 199 (1): 22–5. doi:10.1007/BF01192946. PMID 8067059.  edit
  17. ^ Murkovic M, Derler K (November 2006). "Analysis of amino acids and carbohydrates in green coffee". J. Biochem. Biophys. Methods 69 (1-2): 25–32. doi:10.1016/j.jbbm.2006.02.001. PMID 16563515. 
  18. ^ TEUTSCH, IA, 2004, Einfluss der Rohkaffeeverarbeitung auf Aromastoffveränderungen in gerösteten Kaffeebohnen sowie im Kaffeebetränk, PhD Thesis, Department of Chemistry, Technical University Munich, Germany; www.deposit.ddb.de/cgi-bin/dokserv?idn=97339305x& dok_var=d1&dok_ext=pdf&filename=97339305x.pdf
  19. ^ GINZ, M (2001). "Bittere Diketopiperazine und chlorogensäurederivate in Roestkaffee". PhD-thesis, Technical University Carolo-Wilhelminia, Brunswig, Germany
  20. ^ Redgwell RJ, Curti D, Rogers J, Nicolas P, Fischer M (June 2003). "Changes to the galactose/mannose ratio in galactomannans during coffee bean (Coffea arabica L.) development: implications for in vivo modification of galactomannan synthesis". Planta 217 (2): 316–26. doi:10.1007/s00425-003-1003-x. PMID 12783340. 
  21. ^ GOTODA, N, IWAI, K, Arabinogalactan isolated from coffee seeds indicates immunomodulating properties, p. 116-120; In: Association for Science and Information on Coffee, (ASIC) 21st International Conference on Coffee Science, 11 – 15 September 2006, Montpellier, France
  22. ^ TRESSEL, R, HOLZER, M and KAMPERSCHROER, H, 1983, Bildung von Aromastoffenin Roestkaffee in Abhaengigkeit vom Gehalt an freien Aminosaeren und reduzierenden Zuckern; 10th International Colloquium Chemicum Coffee, Salvador, Bahia 11 October to 14 Oct; ASIC publication 1983, p279-292
  23. ^ ROFFI, J, CORTE DOS SANTOS, A, MEXIA, JT, BUSSON, F, and MIAGROT, M, 1973, Café verts et torrefiesde l Angola. Etude chimique, 5th International Colloquium Chemicum Coffee, Lisboa, 14 June to 19 June 1971; published by ASIC 1973, pp 179-200
  24. ^ Clifford MN (1985). "Chemical and physical aspects of green coffee and coffee products". In Clifford MN, Wilson KC. Coffee: botany, biochemistry, and production of beans and beverage. London: Croom Helm AVI. pp. 305–74. ISBN 0-7099-0787-7. 
  25. ^ Lee KJ, Jeong HG (September 2007). "Protective effects of kahweol and cafestol against hydrogen peroxide-induced oxidative stress and DNA damage". Toxicol. Lett. 173 (2): 80–7. doi:10.1016/j.toxlet.2007.06.008. PMID 17689207. 
  26. ^ CLIFFORD, M.N, (11–15 September 2006). "Chlorogenic acids – their characterisation, transformation during roasting, and potential dietary significance,". In: Association for Science and Information on Coffee, (ASIC) 21st International Conference on Coffee Science,. , Montpellier, France, p 36-49
  27. ^ MORISHITA, H., KIDO, R. (April 1995). "Anti-oxidant activities of chlorogenic acid".  16th international colloqu. Chem. Coffee, Kyoto 9-14th April,
  28. ^ Bessière-Thomas, Yvonne; Ivon Flament (2002). Coffee flavor chemistry. Chichester: John Wiley & Sons. ISBN 0-471-72038-0. 

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