Chemical changes during coffee roasting

CFRR – The process of roasting coffee creates a chemical change in the compounds found in the green kernel and determines much of the flavor of the coffee.

Coffee is a bean of the coffee plant, which after harvesting, people can create a good cup of coffee. “Seed to cup” is a routine in that each stage has chemical compounds. They have the most pronounced transformation, so it is possible to recognize them by sense during roasting.

Chemical compounds present in green bean 

Carbohydrate

As the major components of free sugars and polysaccharides that account for more than 50-60% of the weight of green coffee beans (Trugo and coworkers, 1985), the importance of carbohydrates due to complex changes in the roasting process contributes to the flavors in coffee drinks. Carbohydrates develop during fruit growth. Free sugar is a precursor to the aromas and flavors of roasted coffee beans, including glucose and fructose, but the most important is sucrose (about 6-7%).

At the fruit ripening stage, an abundance of sucrose was found (Garrett and coworkers, 2016), which contributed to the formation of flavor molecules in roasted coffee. The amount of this sugar depends on the degree of ripening of the fruit and the cultivar in arabica beans, where the concentration will be higher than in robusta beans (Campa and coworkers, 2004; Clarke and coworkers, 2008). Sucrose is concentrated in the endosperm and evenly distributed, while glucose and fructose are located mainly in the silver shell (Redgwell and coworkers, 2006).

Polysaccharides include galactomannan, arabinogalactan-protein, cellulose, a small amount of pectic polysaccharide, and xyloglucan (Redgwell and coworkers, 2002; Oosterveld and coworkers, 2003).

Alkaloids

The main alkaloids to mention are caffeine and trigonelline.

Caffeine accounts for 1-4%, depending on the type of coffee beans and plant variety (Belitz and coworkers, 2009; Mazzafera and coworkers, 2010). In arabica beans, caffeine is from 0.9-1.7%, while in robusta beans, the caffeine content is double as 1.8-4%. Caffeine contributes about 10% bitterness and is a stimulating property of the central nervous system, increases blood circulation, and is well known for its effects on increasing alertness Protein makes up about 13-16% by weight in green coffee beans with the form of a- and B- legumin (Bau and coworkers, 2001), enzymes, and amino acids. These amino acids react with free sugars participating in the Maillard chain reaction that occurs during roasting, contributing to the browning of the beans, aroma, and flavor of brewed coffee (Kitzberger and coworkers, 2016). Amino acids participate in Strecker decomposition in roasting to form aldehydes (Rizzi, 2008). 2006, Belitz and coworkers, 2009).

Trigonellin (N-methylnicotinic acid C7H7NO2) up to 0.8% in green coffee beans, melting point is 218 degrees Celsius. Under the effect of heat, Trigonellin will be hydrolyzed 50% to form Nicotinic acid (precursor of vitamin PP has a cholesterol-reducing effect), pyridine, 3-methyl pyridine, methyl ester… In the chemical composition, there will be no nicotinic acid, it is only formed only in trigonelline hydrolysis (Lang and coworkers, 2008).

Organic acids

Major acid in coffee includes citric, acetic, lactic, malic, and y-aminobutyric acids (GABA) (Kramer and coworkers, 2010). Other acids exist in lipid-soluble compounds called fatty acids, chlorogenic acids in phenolic compounds that contribute to sour and bitter flavors in coffee, and succinic, gluconic, and fumaric acids with small amounts (Bahre, 1996).

Lipid

The lipid-soluble content of arabica beans is about 15-17%, and robusta beans are about 7-10% (Farah, 2012). Triacylglycerols (TAGs) consist of linoleic, oleic, and linolenic acids about 75%, diterpenes including cafestol and kahweo about 20%, sterols 5.5%, free fatty acids 1%, phospholipids 0.5%, tocopherols 0.05% (Kolling and coworkers associates, 2005). The content of lipid-soluble compounds is lower than that of other compounds, so it is suggested that fat composition is less related to coffee quality (Caporaso and coworkers, 2021).

Proteins and amino acids 

Protein makes up about 13-16% by weight in green coffee beans with the form of a- and B- legumin (Bau and coworkers, 2001), enzymes, and amino acids. These amino acids react with free sugars participating in the Maillard chain reaction that occurs during roasting, contributing to the browning of the beans, aroma, and flavor of brewed coffee (Kitzberger and coworkers, 2016). Amino acids participate in Strecker decomposition in roasting to form aldehydes (Rizzi, 2008).

The content and composition of proteins in the two types of arabica and robusta were not significantly different overall (Folstar, 1985). However, there is still controversy about the protein ratio related to the organoleptic property, Franca and coworkers reported that higher protein content is associated with higher quality (Franca and coworkers, 2005, but there is an opposite report that lower protein intake resulted in higher. (Barbosa and coworkers, 2019)

The average free amino acid content of robusta is higher than that of arabica beans (Arnold and coworkers, 1994). That accords with the quality of arabica and robusta beans. When the content of free amino acids is higher, they inhibit some compounds, such as 2-furaldehyde and furanone. They affect the flavor and associate melanoidin formation with roasted coffee color. Excessively high levels of free amino acids can reduce the quality of brewed coffee (Poisson and coworkers, 2009), the same study found the presence of cysteine as one of two amino acids with sensation-related death.

Although free cysteine is not present in green coffee beans (Arnold et al., 1996), cyteine derivatives such as glutathione or the cysteine-rich protein are precursors of this flavor.

Basic roasting process 

Physical change

 Roasting is the physical and chemical transformation from green coffee beans into roasted coffee beans. Roasters can experiment and select the right roasting profile for each type of coffee bean according to their desired purpose. According to John (2009), the coffee roasting process takes place with the following physical changes:

• Change in color

When green coffee loses moisture, it will turn from green to light yellow, then to continue roasting, the beans will turn from light – yellow to light – brown to dark brown

• The first crack

When the temperature reaches 193-204°C, the particle size will increase, and the moisture and the generated gases are released outside by the crack with the first explosion.

• Caramelization

After the start of the first explosion, at this stage, the coffee beans will turn dark brown very quickly. It takes thorough observation and time to achieve the correct level of roasting.

• The second crack

The second crack will be hard to identify than the first at this step, the bean’s color can change in such a fraction moment.

• End of roasting

As reaching the desired roastery, the coffee bean is brought to cool quickly.

Chemical change 

Parallel to physical change is chemical reactions that form long aromas, sourness, sweetness, balance, and aftertaste. ACS – American Chemical Society has concluded the following:concluded on the transformation of chemical compounds during roasting as follows:

• Maillard reaction

The reaction occurs at temperatures between 150-200°C, carbonyl groups and amino groups in proteins participate in the reaction to form flavor compounds, there are hundreds of coffee flavor compounds formed in this reaction.

• Caramelization

The reaction occurs when the temperature reaches 170-200°C which stage, the sugar in coffee participates in the caramelization reaction, contributing to the release of aromatic compounds, and most of the sucrose converted into caramel compounds.

• The first crack

If water inside the bean drained out, the particle size increased by about 50%, and the weight decreased by 5% due to dehydration.

• Pyrolysis:

At about 22°C, the temperature changes the chemical substances in the beans, releasing CO2 gas. The weight is reduced by about 13%, and the color of the beans turns to medium brown.

• Second Crack

The pyrolysis process continues when the roasting temperature reaches 225-230°C, and the cellulose in the bean cell wall is broken, forming a second crack. The beans turn dark brown and begin to appear with a glossy oil coating on the outside of the roasted coffee beans.

Roasting time – Roasting temperature

The roasting temperature and time will depend on the roaster, which is determined by the degree of roasting based on the actual color of the beans when viewed visually. The roaster will divide by color from green coffee beans, yellow beans, light brown, and dark brown to identify light, medium and dark roasting. (Herawati and coworkers, 2019).

Some compounds, such as phenolic, alkaloid, and terpenoid, were beneficial to health (Ding and coworkers, 2014; Ludwing et al., 2012). However, the phenolic and chlorogenic acid compounds degraded during roasting. (Herawati and coworkers, 2019).

The drying phase – endothermic reaction humidity of 10-12% decreases to about 2.5%. The mass of grain decreases significantly from the early stages of roasting from the golden transition, and the smell of bread begins to appear (Herawati and coworkers, 2019).

After the endothermic reaction takes place, the actual roasting phase begins to continue the chemically changed compounds dramatically, the pyrolysis of important flavor compounds. Starting around 190°C – 210°C several reactions such as lipid oxidation, maillard, and caramelization occur simultaneously in this process, and volatile compounds are also released (Kocadagli and coworkers, 2012). The final rapid cooling stage is intended to stop the ongoing reactions, limiting unwanted compounds.

The roasting levels that determined by correlation based on color, time, and temperature. Roasting levels that describe as light, medium, or dark. Where time is a factor that can affect the reactions in the beans, a long roasting time will produce a bitter taste and lack of aroma short roasting time with a high temperature doesn’t have enough time to complete the reaction, which leads to underdeveloped flavors. (Roberto and coworkers, 2003)

Roast Levels

According to Kim and coworkers (2018), roasting levels have divided into several steps based on the color change during roasting. The several levels of roasting based on the sound of the separation process when the coffee beans crack can be determined as follows:

• Light (light roast) – the start of the first sound
• Medium (medium roast) – the end of the first one.
• Medium-dark – the start of the second sound
• Dark roast – the end of the second one.

Sample	Method	Conclusion	Reference
Arabica	Agtron Spectrophotometer	Light-moderate light: 80.8 Moderate light-medium light: 71.8 Medium light-medium: 62.3 Medium-moderate dark: 48.5 Moderate dark-dark: 40.5 Dark-very dark: 32.3	Pires and coworkers, 2021
Arabica	Reduced amount (%)	Light: 14% Medium: 15% Dark: 19%	Rao and coworkers, 2020
Robusta	Acidity (pH)	Light: 5.27 Medium: 5.53 Dark: 5.66	Schenker and coworkers, 2017
Robusta	Acidity (titration method)	Light: 0.31% Medium: 0.24% Dark: 0.22%	Lee and coworkers, 2013

The weight loss reduction rate of coffee beans that light roasted is about 14%, medium roast about 15%, and dark roast 19% (Franca and coworkers, 2009; Hecimovic and coworkers, 2011). The roast level is assessed based on the pH meter and titration method. Light roast coffee will have the highest acidity, and dark roast will have the lowest rate. (Lee and coworkers, 2013).

The color change in coffee is also based on the agtron value, the intensity of coffee from light roast to dark roast can be reduced from 90.8 to 32.3 (Budiastra and coworkers, 2020). The regulation of temperature and color of roasted coffee beans is closely related to the aroma and flavor of brewed coffee.

Advances in measurement technology contribute to the determination of the desired roast level. The two accepted industry standards for the quality of coffee include scores of sensory attributes in brewed coffee and the agtron scale for classifying roasting levels.

According to SCA (2018), an agtron analyzer with the ability to use near-infrared energy outside the spectrum to evaluate changes to the quinon group of compounds. Since quinone variability is predictable and quantifiable directly related to aroma and flavor in brewed coffee, quinon becomes a target for spectroscopic measurements. The lower the score in the analyzer, the darker the roast. Agtron, 2004 analyzes the roast level and scores according to the SCA standards as follows:

Roast Levels	Very Light	Light	Medium light	Medium	Medium dark	Dark	Very dark
Agtron “Gourmet”	85	75	65	55	45	35	25
Agtron “commercial”	64.3	56.9	49.4	42	34.6	27.1	19.7

Agtron has two scales used in the coffee industry, gourmet agtron and commercial agtron. In which the gourmet scale is provided with higher resolution, it shows a more pronounced difference in the scale between the roast levels.

The change of precursors

Main reactions

The study by Illy and coworkers, 1995; Reineccius, 1995; SemmeIroch and coworkers, 1995, presented complex reactions during roasting.

Maillard that occurs during roasting is a complex series of reactions including sugar breakdown, reactions between nitrogenous substances (proteins, peptides, amino acids, seroto-nine, trigonelline), and pyrolysis (Kocadagli and coworkers, 2012), to create aminoaldose and aminoketone by condensation.

• The reaction between free sugars and amino acids produces a Schiff base, which produces low molecules in volatile and non-volatile compounds.
• The reaction produces melanoidin that contributes to the yellow-brown color in coffee from the polymerization of the compound ketamine (Herawati and coworkers, 2019).
• The maillard and pyrolysis reactions produce CO2 a gas that is released when the coffee bean cracks, most of which is still inside the bean and is released slowly after the end of the roasting process. The release of air when roasting increases the pressure of the coffee beans to more than 10 bar, and the volume of roasted coffee beans gradually expands (Schenker and coworkers, 2017).

A Strecker decomposition reaction follows that consists of a reaction between amino acids and dicarbonyls to form aminoketones, pyruvaldehyde, and diacetyl. These newly formed compounds further react with ammonia and hydrogen sulfide to develop pyrazine, pyridine, pyrrole, and furan compounds that contribute to the flavor of brewed coffee (Hustiany, 2013).

The degradation of CGA liberates caffeic acid, which enhances bitterness, and also forms lactones and phenol derivatives responsible for taste and aroma (Ginz and coworkers, 1995; Variyar and coworkers, 2003).

Formic, acetic, glycolic, and lactic acids increase during roasting, where sucrose acts as a precursor of these acids, so different amounts of sucrose will result in veriety amounts of final acid (Ginz and coworkers, 2000). The citric and malic acids in green coffee beans degrade to succinic, fumaric, maleic, and others (Balzer, 2008).

The decomposition reaction of sulfur amino acids such as cysteine and methionine are converted to mercaptan, which continues to react with intermediates of the maillard reaction.

The breakdown of hydroxy amino acids such as serine and threonine can react with sucrose to form alkyl pyrazine.

The breakdown of trigonelline to alkyl pyridines and pyrroles.

The breakdown of quinic acid radicals to form phenols.

Most of the carotenoid pigments will disappear.

Flavors are created from ingredients

Lipids are only partially involved in the roasting process to create coffee flavor. Volatile compounds related to the senses include aldehydes, ketones, etc. (Sunarharum and coworkers, 2014). The free amino acids had almost broken down during roasting. Trigonelline degraded partially during roasting and converted to nicotinic acid and volatile compounds such as pyridine (Viani and coworkers, 1974).

After the roasting process, substances change and no longer resemble the aroma and flavor compounds in the previously identified green coffee. The roasting process loses some water, pyrolysis volatiles, polysaccharides, sugars, amino acids, and chlorogenic acids are significantly reduced, organic acids and lipids are relatively increased, caffeine and trigonelline (N-methyl nicotinic acid) concentrations were almost constant (Roberto and coworkers, 2003).

Thus, the chemical components remaining after the roasting process are volatile and non-volatile, and the aroma components in coffee beans after roasting have formed basic taste sensations such as sourness, bitterness, and astringent tongue.

Research from Illy and coworkers, 1995; Clarke and coworkers, 1987; Illy and coworkers, 1997, determined the density of non-volatile substances in roasted coffee including:

• Caffeine contributes to the strength, body, and bitterness of brewed coffee.
• Trigonelline, nicotinic acid, and N-methyl nicotinamide provide values that define the coffee roaster flavor.
• Proteins and peptides do not undergo the maillard reaction.
• Polysaccharides: cellulose, hemicellulose, arabinogalactan, and pectins that hold volatiles
• Humic acid and melanoidin are the end product of the maillard reaction, which gives roasted coffee its characteristic brown color.
• Chlorogenic acid after pyrolysis forms cinnamic, caffeic, ferulic, ferulic, sinapic, and quinic acids that all have the effect of bitter and astringent taste.
• Minerals: potassium (about 40%), manganese metal (10-50ppm), iron (15-40ppm), copper (2-5ppm).
• Increased formic, acetic, glycolic, and lactic acids are responsible for the sour taste in coffee.

De Morais and coworkers (2008) analyzed three levels of light-medium-dark roasting for robusta coffee beans and analyzed the chemical compositions as follows:

• The total phenol content decreased as the degree of roasting increased.
• The concentration of proanthocyanidins increased as the level of roasting increased.
• Chlorogenic acid decreases as the level of roasting increases.
• The 5-caffeoylquinic acid (5-ACQ) was determined to be higher in light and medium roasts and lower in dark roasts compared to arabica beans.

Nascimento and coworkers (2007) analyzed the compounds of volatile and aroma found to be highest at the light roast.

Conclusion:

The roasting process is considered the time to flavor the coffee beans according to the roaster’s wishes based on the existing fresh bean qualities. The chemical changes of compounds with temperature in this process are not exactly the same between different types of coffee. Therefore, roasters need to understand the general principles of chemical and physical changes in coffee beans during roasting. From there, conduct different tests with the beans you have to find the most reasonable roasting profile, in order to produce the desired coffee flavor.

Reference:

Abdul Majid N A, Edzuan Abdullah M F and Diana A 2015 A Review of Quality Coffee Roasting Degree Evaluation J. Appl. Sci. Agric. 10 18–23 

AGTRON. (2004) AGTRON M-BASIC/II. COFFEE ROAST ANALYZER OWNERS’ MANUAL. Special Applications: Abridged Spectrophotometer, Agtrom Inc. 

American Chemical Society. www.acs.org/content/dam/acsorg/pressroom/reactions/infographics/why-does-your-coffee-taste-and-smell-delicious.pdf

Andrade, C.; Perestrelo, R.; Camara, J.S. Valorization of Spent Coffee Grounds as a Natural Source of Bioactive Compounds for Several Industrial Applications—A Volatilomic Approach. Foods 2022, 11, 1731. https://doi.org/10.3390/ foods11121731 

A.Oosterveld, J.S. Harmsen, A.G.J. Voragen, H.A. Schols. Extraction and characterization of polysaccharides from green and roasted Coffea arabica beans Carbohydrate Polymers, 52 (3) (2003), pp. 285-296

A.S. Franca, J.C.F. Mendonça, S.D. Oliveira. Composition of green and roasted coffees of different cup qualities. LWT – Food Science and Technology, 38 (7) (2005), pp. 709-715,

Balzer, H. H. 2008. Acids in coffee. In Coffee: Recent developments, ed. Ronald Clarke, and O. G. Vitzthum, 18–32. Hoboken, NJ, USA: John Wiley & Sons. 

Barbosa, M. de S. G., Scholz, M. B. dos S., Kitzberger, C. S. G., & Benassi, M. de T. (2019). Correlation between the composition of green Arabica coffee beans and the sensory quality of coffee brews. Food Chemistry, 292(April), 275–280

Belitz, H. -D., Grosch, W., & Schieberle, P. (2009). Food chemistry (4th ed.). Heidelberg: Springer (Chapter 21).

Budiastra I W 2020 Determination of trigonelline and chlorogenic acid (CGA) concentration in intact coffee beans by NIR spectroscopy Agric. Eng. Int. CIGR J

C. Campa, J.F. Ballester, S. Doulbeau, S. Dussert, S. Hamon, M. Noirot Trigonelline and sucrose diversity in wild Coffea speciesFood Chemistry, 88 (1) (2004), pp. 39-43

Clarke RJ, Macrae R. Coffee Technology, vol 2. Elsevier: London, 1987

de Morais, S. A. L., de Aquino, F. J. T., Nascimento, E. A., Oliveira, G. S., Chang, R., Santos, N. C., & Rosa, G. M. (2008). Bioactive compounds, acids groups and antioxidant activity analysis of arabic coffee (Coffea arabica) and its defective beans from the Brazilian savannah submitted to different roasting degrees. Food Science and Technology, 28, 198–207

Ding M, Bhupathiraju S N, Chen M, van Dam R M and Hu F B 2014 Caffeinated and Decaffeinated Coffee Consumption and Risk of Type 2 Diabetes: A Systematic Review and a Dose-Response Meta-analysis Diabetes Care 37 569–86

D. Kramer, B. Breitenstein, M. Kleinwchter, D.Selmar. Stress metabolism in green coffee beans (coffea arabica l.): Expression of dehydrins and accumulation of GABA during drying Plant and Cell Physiology, 51 (4) (2010), pp. 546-553

Fadri R A, Sayuti K, Nazir N and Suliansyah I 2019 The Effect of temperature and roasting duration on physical characteristics and sensory quality of Singgalang Arabica Coffee (Coffea arabica) Agam Regency J. Appl. Agric. Sci. Technol. 3 189–201 

Farah, A. (2012). Coffee Constituents. In Coffee: Emerging Health Effects and Disease Prevention (pp. 21–58)

Farah, A., & Donangelo, C. M. (2006). Phenolic compounds in coffee. Brazilian Journal of Plant Physiology, 18, 23–26

F. Bähre. Electrophoretic clean-up of organic acids from coffee for the GC/MS analysis. Fresenius’ Journal of Analytical Chemistry, 355 (2) (1996), pp. 190-193

Folstar, P. (1985), Lipids. In: Clarke, R. J., & Macrae, R. (Eds.), Coffee Chemistry (Vol. 1, pp 203–222). London, New York: Elsevier Applied Science.

Franca A S, Oliveira L S, Oliveira R C S, Agresti P C M and Augusti R 2009 A preliminary evaluation of the effect of processing temperature on coffee roasting degree assessment J. Food Eng. 92 345–52 

John H Kuper Jr. 2009. BASICS OF COFFEE ROASTING 

Mazzafera, P., & Silvarolla, M. B. (2010). Caffeine content variation in single green Arabica coffee seeds. Seed Science Research, 20, 163–167.

Nascimento, E. A., de Aquino, F. J., do Nascimento, P. M., Chang, R., & de Morais, S. A. (2007). Constituintes voláteis e odorantes potentes do café conilon em diferentes graus de torra. Ciencia y Engenharia/Science and Engineering Journal, 16, 23–30. 

Ginz M; Enhelhardt UH (1995) Analysis of Bitter fractions of Roasted Coffee by LC-ESI_MS- New Chlorogenic acid derivatives. In: Proc. 16th Int. Sci. Coll. Coffee (Kyoto) ASIC, Paris. 

G.P. Rizzi. The Strecker degradation of amino acids: newer avenues for flavor formation. Food Reviews International, 24 (4) (2008), pp. 416-435

Hečimović  I,  Belščak-Cvitanović A,  Horžić  D and Komes D 2011 Comparative study of polyphenols and caffeine in different coffee varieties affected by the degree of roasting Food Chem. 129 991–1000

Herawati D, Giriwono P E, Dewi F N A, Kashiwagi T and Andarwulan N 2019 Critical roasting level determines bioactive content and antioxidant activity of Robusta coffee beans Food Sci. Biotechnol. 28 7–14 

Hustiany R 2013 Reaksi Maillard Pembentuk Citarasa Dan Warna Pada Produk Pangan vol 53 

Illy E. The seduction of espresso. Presented at the 9th Annual SCCA Conference and Exhibition, New Orleans, 1997. 

Illy A, Viani R. Espresso Coffee: The Chemistry of Quality. Academic Press: London, 1995. 

Kitzberger, C. S. G., Scholz, M. B. dos S., Pereira, L. F. P., da Silva, J. B. G. D., & Benassi, M. de T. (2016). Profile of the diterpenes, lipid and protein content of different coffee cultivars of three consecutive harvests. AIMS Agriculture and Food, 1(3), 254–264.

Kocadagli T, Göncüoglu N, Hamzalioglu A and Gökmen V 2012 In depth study of acrylamide formation in coffee during roasting: Role of sucrose decomposition and lipid oxidation Food Funct. 3 970–5 

Kölling-Speer, I., Kurzrock, T., Gruner, M., & Speer, K. (2005). Formation of a new substance in the lipid fraction during the storage of green coffee beans. In T. Eklund, M. Schwarz, H. Steinhart, H.-P. Thier, P.Winterhalter (Eds.), Proceedings of Euro Food Chem, XIII, 21–23. September, Hamburg, Germany (Vol. 2, pp. 491–494). ISBN: 3-936028-32-X.

Kim S Y, Ko J A, Kang B S and Park H J 2018 Prediction of key aroma development in coffees roasted to different degrees by colorimetric sensor array Food Chem. 240 808–16

Koshiro, Y., Zheng, X. -Q., Wang, M. -L., Nagai, C., & Ashihara, H. (2006). Changes in content and biosynthetic activity of caffeine and trigonelline during growth and ripening of Coffea arabica and Coffea canephora fruits. Plant Science, 171, 242–250 

Lang, R.; Yagar, E.F.; Eggers, R.; Hofmann, T. Quantitative investigation of trigonelline, nicotinic acid,and nicotinamide in foods, urine, and plasma by means of LC-MS/MS and stable isotope dilution analysis.J. Agric. Food Chem. 2008,56, 11114–11121

L. Poisson, F. Schmalzried, T. Davidek, I. Blank, J. Kerler. Study on the role of precursors in coffee flavor formation using in-bean experiments Journal of Agricultural and Food Chemistry, 57 (21) (2009), pp. 9923-9931

Lee M J, Kim S E, Kim J H, Lee S W and … 2013 A study of coffee bean characteristics and coffee flavors in relation to roasting J. Korean …

Ludwig I A, Sanchez L, Caemmerer B, Kroh L W, De Peña M P and Cid C 2012 Extraction of coffee antioxidants: Impact of brewing time and method Food Res. Int. 48 57–64

Michael Ginz, Hartmut H. Balzer, A. G. W. Bradbury & Hans G. Maier European Food Research and Technology volume 211, pages 404–410 (2000). Formation of aliphatic acids by carbohydrate degradation during roasting of coffee

N. Caporaso, M.B. Whitworth, I.D. Fisk. Total lipid prediction in single intact cocoa beans by hyperspectral chemical imaging. Food Chemistry, 344 (2021), Article 128663

Pires F de C, Pereira R G F A, Baqueta M R, Valderrama P and Alves da Rocha R 2021 Near- infrared spectroscopy and multivariate calibration as an alternative to the Agtron to predict roasting degrees in coffee beans and ground coffees Food Chem. 365

Rao N Z, Fuller M and Grim M D 2020 Physiochemical characteristics of hot and cold brew coffee chemistry: The effects of roast level and brewing temperature on compound extraction Foods 9 1–12 

R. Clarke, O.G. Vitzthum Coffee: Recent developments Wiley-Blackwell, Hoboken, USA (2008)

R. Garrett, C.M. Rezende, D.R. Ifa. Revealing the spatial distribution of chlorogenic acids and sucrose across coffee bean endosperm by desorption electrospray ionization-mass spectrometry imaging LWT – Food Science and Technology, 65 (2016), pp. 711-717

Redgwell RJ, Curti D, Fischer M, Nicolas P, Fay LB (2002a) Coffee bean arabinogalactans: Acidic polymers covalently linked to protein. Carbohyd. Res. 337:239-253.

Reineccius GA. In Proceedings of the 16th ASIC Meeting, 1995, Kyoto; 249–257. 

R.J. Redgwell, M. Fischer Coffee carbohydrates Brazilian Journal of Plant Physiology, 18 (1) (2006), pp. 165-174

R.J. Redgwell, D. Curti, M. Fischer, P. Nicolas, L.B. Fay Coffee bean arabinogalactans: Acidic polymers covalently linked to protein Carbohydrate Research, 337 (3) (2002), pp. 239-253

Roberto A. Buffo and Claudio Cardelli-Freire, 2003. Coffee flavour: an overview.

Sara E. Yeager, Mackenzie E. Batali, Jean-Xavier Guinard & William D. Ristenpart, 2021. Acids in coffee: A review of sensory measurements and meta-analysis of chemical composition

Specialty Coffee Association. 2018. Coffee Standards.

Schenker S and Rothgeb T 2017 The Roast-Creating the Beans’ Signature the Craft of Sciece of Coffee ed I Blank, A Farah, P Giuliano, D Sandres and C Wille (London: Academic Press) pp 17–49 

Semmelroch P, Laskawy G, Blank L, Grosch W. Flavour Fragr. J. 1995; 10: 1. 

S.M.T. Baú, P. Mazzafera, L.G. Santoro. Seed storage proteins in coffee. Revista Brasileira de Fisiologia Vegetal, 13 (1) (2001), pp. 33-40

Trugo, L. C. Carbohydrates. In: Coffee, 1st edition, Clarke R. J., Macrae, R., eds. Essex: Elsevier Applied Science Publishers; 1985, Vol 1: Chemistry, p. 83. 

U. Arnold, E. Ludwig. Analysis of free amino acids in green coffee beans: II. Changes of the amino acid content in arabica coffees in connection with post-harvest model treatment. Zeitschrift Fur Lebensmittel -Untersuchung Und -Forschung, 203 (4) (1996), pp. 379-384

U. Arnold, E. Ludwig, R. Kühn, U. Möschwitzer. Analysis of free amino acids in green coffee beans – I. Determination of amino acids after precolumn derivatization using 9-fluorenylmethylchloroformate. Zeitschrift Für Lebensmittel-Untersuchung Und -Forschung, 199 (1) (1994), pp. 22-25

Variyar PS; Ahmad R; Bhat R; Niyas Z; Sharma A (2003) Fla- voring components of raw monsooned arabica coffee and their changes during radiation processing. J. Agric. Food Chem. 51:7945- 7950. 

Viani, R, Horman, I, 1974. Thermal behavior of trigonelline. Journal of Food Science 39 (6), 1216-1217.

W.B. Sunarharum, D.J. Williams, H.E.Smyth. Complexity of coffee flavor: A compositional and sensory perspective. Food Research International (2014)