molecular structure of cafestol in coffee

What Gives Coffee Its Flavor? The Effects of Coffee Chemicals.

December 13, 2022

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What gives coffee its flavor? Which chemicals contribute to the taste, flavor, and aroma of coffee? We’ll explore these questions and more in this comprehensive post on the main chemicals that affects coffee’s flavor, taste, and aroma.

How Does Coffee Get Its Flavor?

Taste and flavor aren’t the same things. Taste refers to the perception of the sensory cells in your taste buds. When food molecules activate these sensory cells, your brain detects a taste, like sweetness. Flavor includes taste and odor (healthline).

Sensory cells contain large molecules called receptors. Molecules interact with receptors and receptors respond. The main response of receptors is to send a signal to the brain via the nervous system.

Molecules from food interact with sensory cell receptors in the tongue and nasal cavity to create various tastes and odors.

Coffee beans contain a complex mixture of thousands of chemicals. These chemicals occur naturally in the raw coffee bean, are produced during coffee bean processing, or are produced while roasting coffee beans.

These coffee chemicals combine to give you a unique sensory experience that includes taste, flavor, and aroma.

Where Does Coffee Get Its Flavor?

We know that the flavors of coffee ultimately depend upon the complex mixture of chemicals in raw and roasted coffee beans.

The amount and proportion of these complex chemicals in coffee determine the final taste, aroma, and flavor of coffee. 

The amount and proportion of the coffee chemicals, in turn, depend upon many factors, including…

  • how the coffee plant is grown (such as type of land, altitude, temperature, soil, rain, and cultivation)
  • type of coffee plant (variety)
  • how coffee is processed (e.g. wet or dry processed)
  • how coffee beans are roasted (e.g. light, medium, and dark roast)
  • how coffee is ground (fine, medium or coarse ground)
  • brew temperature
  • coffee-to-water brew ratio
  • water quality
  • coffee brewing technique
  • and many others…

We will discuss some of these factors in another post. This post will discuss some of the main chemicals responsible for coffee’s taste, aroma, and flavor. First, a very brief chemistry lesson.

What are chemicals, compounds, and molecules?

diagram of relationship between chemical, compound, and molecule

You often see the words chemical, compound, or molecule used in various ways when describing the composition of living things, which can be confusing. Let us briefly review these basic words to understand what is coming. 

A chemical is anything that has matter. Matter has structure, takes up space, and has mass. Thus, a chemical is anything that has structure, takes up space, and has mass. This includes any liquid, solid, or gas. A chemical can be a pure substance or a mixture. A chemical can be natural (in the earth, atmosphere, or water) or man-made (artificial or synthesized).

A natural chemical can also be made through artificial means. 

A molecule is a chemical made from two or more atoms held together by chemical bonds. The atoms may be the same or different. The smallest molecule is made from two atoms, and the largest molecule can be made from millions of atoms.

A compound is a chemical made from two or more different atoms. If all the atoms are the same, it is not a compound but a molecule. The term chemical compound may be used to distinguish the chemical definition of a compound from other non-chemistry uses of the word compound (e.g. a village compound).

As you can see from the definitions above, all molecules and compounds are chemicals. Compounds may be molecules, but not all compounds are molecules.

For many people, the word ‘chemical’ has negative connotations. However, all life is chemical, all food is chemical, and everything we know in the physical world is chemical. That is why chemistry and biochemistry are such important sciences.

Coffee is a plant, an organism, and a living thing. The chemicals in living things are also often known as organic chemicals or biochemicals to distinguish them from chemicals not contained in or used by living things.

For our post, we will use the word chemical or molecule when describing the components of coffee.

Chemicals Are Not Always Bad

Given that all of life is made of chemicals, you can see that chemicals are not always bad. Some chemicals are necessary and good for you. 

The chemicals in coffee can also be good for you, and we have discussed the health benefits of coffee in previous posts.

This post looks at some chemicals responsible for coffee’s good and not-so-good taste, flavor, and aroma.

Classification of Organic Chemicals

There are millions of organic chemicals, so to make things easier to understand, scientists classify them into different types based on their structure and function or both.

However, given the large number of organic chemicals, there are also a similarly large number of types. A classification system is never perfect; one chemical may be classified in different ways or be present in different classifications.

The classifications also use scientific terms that may be confusing, strange, and maybe even a little scary. Don’t worry, you don’t need to remember all of these terms.

You may not know these chemical types, but you will know which have particular flavor characteristics.

If you want to learn more, you may like to read more about classifications used in organic chemistry. Visit your library, read a few textbooks, or look at Wikipedia or masterorganic chemistry sites. 

What chemicals are responsible for coffee’s flavor?

Like any other organic organism, raw coffee beans contain a complex mixture of thousands of large and small molecules (Saud&Salamatullah 2021).

Which chemicals are found in coffee? The main chemicals in coffee (Pinheiro and others, 2020) and their approximate proportions include…

  • Lipids (10 to 17%)
  • Chlorogenic acids (3 to 10%)
  • Trigonelline (1 to 2%)
  • Caffeine (1 to 2%)
  • Ash (4%)
  • Polysaccharides (44 to 48%)
  • Sucrose (4 to 8%)
  • Lignin (3%)
  • Protein (11%)
  • Pectin (2%)
  • Amino acids (0.8%)
  • Thousands of other smaller chemicals (remaining percent)

The amount and proportion of these chemicals vary depending on the coffee variety, farming conditions, and many other conditions discussed previously.

Main Chemical Types in Coffee

Raw (green) and roasted coffee beans also contain thousands of smaller chemicals, some of which contribute to the taste and aroma of coffee.

The following lists some of the major chemical types (categories) in coffee…

  • Volatile and Non-volatile molecules
  • Melanoidins
  • Alkaloids
  • Phenolic Acids
  • Flavonoids
  • Terpenoids
  • Organic Acids
  • Alcohols
  • Aldehydes and Ketones
  • Amines
  • Esters
  • Oils
  • Sugars

Volatile and Non-Volatile Molecules

The chemicals in coffee can be divided into volatile and non-volatile chemicals.

Nonvolatile molecules do not tend to evaporate and remain within water or oil in the coffee bean or brewed coffee. Non-volatile components of coffee include large molecules (carbohydrates, proteins, lipids), melanoidins, minerals, alkaloids, and chlorogenic acid

Non-volatile compounds can break down from the effect of heat during roasting, but some remain to contribute to coffee’s flavor. Some of coffee’s non-volatile chemicals may also interact with coffee’s volatile chemicals to affect the taste and flavor of the coffee (Saud&Salamatullah 2021).

When coffee beans are roasted, chemical reactions take place between existing chemicals in the coffee bean to produce new chemicals which can be volatile. 

Chlorogenic acid and trigonelline rapidly degrade during roasting, producing phenolic compounds and pyridines/pyrroles. 

Volatile molecules evaporate into gases at room temperature but also during heating and are released into the air. These molecules affect the aroma of coffee, especially after roasting or brewing.

More than 800 kinds of coffee aroma components have been identified and analyzed. 

These volatile molecules occur naturally in raw (green) coffee beans, they can be produced during processing, roasting, and brewing coffee.

Melanoidins

Melanoidins are natural non-volatile high-weight chemicals that increase in amount during coffee bean processing and roasting. They are produced by a general organic reaction involving heat called the Maillard Reaction.

The chemical structure of coffee melanoidins remains disputed but they can be small or large chemicals.

Melanoidins may contribute to the bitterness and astringency of coffee and the characteristic taste and brown color of roasted coffee beans.

The Maillard reaction is a chemical reaction that occurs between amino acids and reducing sugars.

The Maillard chemical reaction has the greatest effect during roasting but also occurs naturally during plant growth and coffee bean processing.

Alkaloids

The main non-volatile alkaloid of coffee is caffeine (1,3,7-trimethylxanthine) which is responsible for the bitter taste of coffee.

As you know, caffeine is one of the most abundant chemicals in coffee.

caffeine molecule
Molecular Structure of Caffeine an example of an alkaloid

Other coffee alkaloids include trigonelline, theobromine (also found in cocoa and chocolate), nicotinic acid and theophylline are found in raw coffee beans or produced during roasting.

About 14 different alkaloids have been identified and analyzed in raw or roasted coffee beans (Saud&Salamatullah 2021).

The combined effects of these alkaloids give coffee its strength, bitter taste, body, and aroma. Trigonelline in particular contributes to the roast and brewed coffee aroma.

Phenolic Acids

Over 60 phenolic acids and polyphenols have been found in raw or roasted coffee beans (Saud&Salamatullah 2021). Some of these are volatile and some are non-volatile.

Chlorogenic acid is the main non-volatile polyphenol molecule in green and roasted coffee. It has a higher concentration in the green coffee bean than caffeine.

chemical structure of chlorogenic acid
Chemical Structure of Chlorogenic Acid

Chlorogenic acid contributes to coffee’s astringent, sweet, and sour tastes. Chlorogenic acid is also thought to be the source of the unpleasant taste after prolonged coffee brewing (Kunisuke Izawa, 2010).

Chlorogenic acid in coffee beans decreases during roasting due to chemical transformation to other molecules.


infographic on why coffee is bitter
Courtesy of Compound Chem under Creatives Common Licence

Flavonoids

Flavonoids are natural molecules containing phenol chemical groups (Wikipedia). They are also a class of polyphenols mentioned previously. Their name hints at their contribution to flavor. 

About 25 flavonoids have been found in raw or roasted coffee beans (Saud&Salamatullah 2021).

chemical structure of cianidanol
Cianidanol is an example of a flavonoid

Some key flavonoids in coffee include quercetin, kaempferol, cianidanol, and myricetin.

Flavonoids may contribute to the sour flavors and bitter taste of coffee.

Terpenoids

Terpenoids, also known as isoprenoids, and their related chemicals, such as terpenes and diterpenes, are natural plant chemicals. Diterpenes are also a class of polyphenols. Terpenoids and their related chemicals are usually fragrant oils.

Kahweol is an example of a terpenoid

The main terpenoids of coffee are kahweol, cafestol, and 16-O-methylcafestol.

Organic Acids

There are many simple organic acids in coffee. The word simple refers to a simpler structure than larger phenolic acids such as chlorogenic acid.

The Specialty Coffee Association has picked out about six common organic acids that seem to have a major impact on the flavor of coffee. The six organic acids include acetic acid (vinegar), lactic acid (also seen in soured milk), citric acid, malic acid, phosphoric acid, and quinic acid.

Chemical structure of Citric Acid

The acids in coffee are responsible for many of the flavors commonly associated with coffee, such as sourness, acidity, and brightness.

Note that when we describe coffee as acidic, we are not always referring to a technical term such as pH (which is a confusing scale) but rather how we sense the taste of the coffee. 

Alcohols

This is not the same as alcohol in drinks but small organic chemicals with a similar structure. 

An example of a common small alcohol in coffee is Furfuryl alcohol.

chemical structure of furfuryl alcohol
Furfuryl alcohol

These small alcohols are responsible for many flavors and aromas commonly associated with coffee, including fruity, floral, and spicy flavors.

Aldehydes and Ketones

Aldehydes and ketones are known for having a fruity and floral fragrance. Coffee contains a range of aldehydes and ketones.

Aldehydes and ketones may be responsible for many flavors and aromas commonly associated with coffee, including floral, citrus, and nutty flavors.


infographic on the aroma of coffee
Courtesy of Compound Chem under Creatives Common Licence

Amines

Amines such as harmane and norharman may contribute to the bitterness of coffee. Different flavor molecules are produced when amines react with sugars in a Maillard reaction. 

Esters

Esters may contribute to a yeasty and fruity flavor of coffee. 

Oils

Coffee contains a range of volatile oils responsible for its distinct aroma. The specific oils and esters present in the coffee and the proportions in which they are present determine the unique aroma of the coffee.

Triglycerides and fatty acids are responsible for many flavors and aromas commonly associated with coffee, including nutty, woody, and earthy flavors.

Sugars

Coffee contains non-volatile sugars such as sucrose, contributing to its sweetness and flavor. The specific sugars present in coffee and the proportions in which they are present can vary depending on the type of coffee and the roasting process.

Sucrose

Characteristic Flavors and Aromas of Coffee

As you can see, many chemicals contribute to coffee’s flavor, taste, and aroma. They also contribute to other characteristics of coffee, such as ‘evenness’ and ‘mouthfeel’.

It isn’t easy to pinpoint exactly which chemicals contribute to a particular flavor profile in coffee. However, characteristic flavor chemicals have been identified in the following groups…

1. aldehydes and ketones are related to caramel/sweet taste

2. Sulfur compounds are associated with sulfur/roasting odor

3. pyrazine compounds were related to soil odor, nuts, and roasted coffee

4. phenols and aldehydes are associated with smoky/phenolic aromas. The phenolic chemical guaiacol is also associated with burnt flavors.

5. furan and furanones are associated with a pungent taste, caramel, and roasted nut, and roasted coffee flavors.

6. Maillard chemicals that occur during the roasting of the coffee beans are responsible for many of the flavors and aromas commonly associated with coffee, including nutty, caramel, and toasty flavors.

7. caramelization of the sugars in coffee beans during roasting produces a range of complex molecules that contribute to the flavor and aroma of the coffee. These molecules give coffee its sweet, rich flavors and aromas.

Not all chemicals are good-tasting, have nice aromas, or have delicious flavors in coffee. Some of the natural chemicals or chemicals produced during roasting can have detrimental effects on taste, aroma, and flavor.

Chemicals in Brewed Coffee and Flavor

A study by scientists (Heo and others 2020) examined the relationship between the chemicals in cold brew coffee and flavor. The research identified 36 volatile chemicals associated with particular tastes, aromas, and flavors.

The table below, adapted from Heo’s research, shows the chemicals and their sensory descriptors (tastes, aromas, and flavors).

ChemicalSensory Description
PyridineSour, Fishy, Burnt, Smoky
Methylpyrazine
FurfuralSweet, Wood, Almond
2-FuranmethanolSweet, Caramel, Coffee
2,6-DimethylpyrazineCocoa, Roasted, Nutty
3-EthylpyridineTobacco, Lethery
5-Methyl-2-furaldehydeCaramel, Coffee
PhenolPhenolic
2-Ethyl-3-methylpyrazineNutty, Peanut, Musty, Earthy
Pyrrole-2-carboxaldehydeMusty, Coffee
3-MethylphenolPhenolic
2-AcetylpyrroleMusty, Nutty
3,5-Octadien-2-oneFruity, Fatty
2-Acetyl-1-methylpyrroleEarthy
3-Ethyl-2,5-dimethylpyrazineNutty
2-Ethyl-3,5-dimethylpyrazineAlmond, Burn, Coffee, Nutty
2,5-DiethylpyrazineSweet
GuaiacolPhenolic, Smoky, Burnt
3-Ethyl-2-hydroxy-2-cyclopenten-1-oneCaramel, Sweet
NonanalWaxy, Rose, Fresh
MaltolCaramel, Sweet
1-FurfurylpyrroleVegetable, Green, Waxy
Methyl salicylateWintergreen, Mint
Nonanoic acidWaxy, Cheese
4-EthylguaiacolSpicy, Sweet
Difurfuryl etherCoffee, Earthy, Mushroom
4-VinylguaiacolWoody, Dry, Roasted, Clove-like
Decanoic acidRancid, Sour, Fatty
3,4-DimethoxystyreneGreen, Floral
Dodecanoic acidFatty
Tetradecanoic acidWaxy, Fatty

Conclusion

In summary, coffee gets its flavor, taste, and aroma from a vast and complex mixture of chemicals in raw and roasted coffee beans.

The specific chemicals in the coffee and the proportions in which they are present determine the coffee’s overall flavor, taste, and aroma.

Some key chemicals that contribute to coffee’s flavor, taste, and aroma include caffeine, acids (organic and phenolic), esters, melanoidins, phenols, polyphenols, aldehydes, ketones, amines, oils, and sugars. 

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chemicals in coffee
Fun Pic – Enjoy your coffee with thousands of chemicals!

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