How Coffee Compounds Determine Flavor and Aroma

coffee alongside food

In this part of the guide we’ll review the important chemicals and chemical reactions that impact the flavor and balance of coffee. We’ll also leave you with a good sense of how flavor and overall quality of coffee is evaluated and judged.

Coffee beans, though small and relatively uninteresting to look at, contain roughly a thousand chemical compounds within.

Ultimately it’s the roasting method and style that will determine what chemical composition the final version of the coffee wil have.

Fats and carbohydrates found in the coffee bean are transformed into oils throughout the roasting process, and it’s these types of chemical reactions that end up sharing the flavor, aroma and taste of the coffee.

The roasting includes two processes that end up significantly influencing and developing the flavor and taste.

The Science of Flavor and Aroma

It turns out that coffee contains hundreds of different compounds that contribute to its unique flavor. Some of these are volatile compounds that are responsible for coffee's characteristic aroma. Others are non-volatile and contribute to the coffee's flavor and body.

Coffee's aroma is largely due to volatile compounds that are released when coffee is roasted. These compounds interact with each other and with the coffee's oils to create coffee's unique smell. Some of the most important compounds responsible for coffee's aroma include coffee oil, ethyl acetate, and coffee aldehyde.

Coffee's flavor is a complex combination of taste and smell. The coffee's body, acidity, sweetness, and bitterness all contribute to its flavor. Non-volatile compounds found in coffee beans are responsible for the coffee's body and sweetness. Some of the most important non-volatile compounds in coffee include coffee lactones, coffee pyrazines, and coffee trigonelline.

The Science of Brewing

Brewing is the process of extracting coffee's flavors and aromas from the coffee beans. The brewing method you use will have a big impact on the final flavor of your coffee. Different brewing methods extract different compounds from the coffee beans.

The coffee brewing process starts with grinding the coffee beans. The grind size you use will have a big impact on the final flavor of your coffee. A finer grind will extract more flavors and aromas from the coffee beans, while a coarser grind will extract fewer.

Tasting Notes

Chemical compounds that impact the tasting notes you'll find in coffee include:

1. Aromatics: These are the volatile oils that give coffee its unique smell. They include compounds like 2-methoxy-4-methylphenol (2-MMP), which has a floral scent, and 4-ethylguaiacol (4-EG), which has a smoky aroma.

2. Bitterness: This is caused by compounds like chlorogenic acids and caffeine.

3. Body: The fullness or thickness of coffee is determined by its soluble solids content, which includes things like sugars, proteins, and lipids.

4. Acidity: Coffee's acidity is due to compounds like quinic acid and citric acid.

5. Sweetness: Coffee's sweetness comes from compounds like sucrose and fructose.

6. Aftertaste: Coffee's aftertaste is determined by a variety of factors, including its acidity, bitterness, and body.

Coffee Molecules and Ingredients

The caffeine in coffee interacts with the adenosine receptors in the brain to provide energy. This is why many people drink coffee in the morning to help them start their day.

Caffeine also blocks adenosine receptors, which is why drinking too much coffee can make you feel jittery.

When you are awake, the neurons in your brain are continually firing, and a by-product of this firing is adenosine, a biochemical compound that is a neuromodulator for the central nervous system.

Your nervous system receptors are constantly monitoring your levels of adenosine, and when they get too high, your brain will slow down neural activity and dilate the blood vessels, making you feel sleepy or crave rest.

Caffeine has a similar molecular structure to adenosine – notably, two nitrogen rings.

This similarity in structure means that caffeine can bind to your nervous system’s adenosine receptors without activating them, effectively blocking the receptors from detecting the levels of adenosine and, therefore, keeping you alert even if those levels may be elevated.

While you are awake, the neurons in your brain are firing. As a result of this firing, adenosine is produced, which is a neuromodulator for the central nervous system.

Your nervous system has receptors that continuously monitor your levels of adenosine. When they get to a level that's too high, your brain slows down neural activity and dilates your blood vessels. This ultimately makes you feel sleepy or crave rest.

1. The Maillard Reaction

What is known as “the Maillard reaction” is what takes place as a result of just about any kind of cooking process. It catalyzes the arranging (or rearranging) and transformations of various amino acids and sugars at a molecular level, and it is that process that enhances and develops the flavor.

2. The Strecker Degradation

The Strecker degradation is the name given to the chemical reaction that impacts both carbonyl compounds and amino acids in combination to produce new flavors.

Acidic Content

In the context of coffee when we refer to “acidity” what we are really referring to is the differing degrees of various acids that might be present in the coffee, the the type and level of acid determining different nuances in flavor.

The right combination of types and levels of acids will lead to more balanced and complex flavors.

Most of the acid content found in coffee is composed of chlorogenic acids and citric acids.

The citric acids add a zest or “brightness” to the coffee flavor in moderate doses but at higher levels they can cause the coffee to develop more sour notes.

Other impactful acids include malic, phosphoric and acetic. These acids are responsible for the development of many other flavors including apple or fruit notes and a certain “biting” kick.


Trigonelline is the alkaloid you’ll find in coffee beans that breaks down and produces vitamins that are good and essential for health. It also contributes to the development of aromatic compounds like pyrroles and pyridines.

Pyrrole and Pyridine

It’s the pyrrole and pyridine compounds that contribute a significant degree to the aroma of the coffee.

Pyrroles can actually lead to the coffee having less than enjoyable flavors, sometimes causing the coffee to taste a bit musty or burnt. Pyrazines tend to deliver notes that will put you in mind of toast or grains.

Ketones and Aldehydes

Ketones are generated during the coffee roasting and have no small effect on the coffee’s aroma.

Aldehydes are also developed through roasting, throughout the exposure of oxygen and carbohydrates. They tend to have an even larger impact on coffee aroma than Ketones.

You’ll find both these molecules in green (unroasted coffee) as well as those developed in roasted coffee.

There are different types of Ketones and Aldehydes and each type will determine the aroma in different ways. For instance some types will lead to a more floral scented brew, while others will create a coffee with a more buttery complexion.


Different types of sugars can be found in coffee but “sucrose” is the most common. Keep in mind that most sucrose is destroyed by the roasting process.

Nevertheless, the presence of sucrose is essential as it, along with other carbohydrates, is critical to the Maillard reaction and forms the essential ingredient in the process of caramelization (browning).

The caramelization process helps to retain much of the sweetness of the coffee and also enhances both the flavor and aroma.

Coffee Cupping

cupping coffee

As you’ll probably gather from all the above notes, there are quite a few elements that influence a coffee’s flavor profile including many we haven’t even mentioned in this guide.

This presents a challenge when evaluating and analyzing all the different notes and constituents that shape a given cup of coffee’s flavor profile - and so the “Cupping method” was established to help evaluate both the flavor and aroma of various coffee beans in a way that allows roasters and other coffee professionals to evaluate to coffee’s comparative merits and quality.

Coffee “cupping” consists of tasting (brewed) coffee with the intention of identifying and evaluating different flavors and aromas.

Coffee cupping can be done by anyone, but professionals who perform coffee cupping and quality evaluation are referred to as "Q Graders".

Coffee Cupping Protocols

The distinctions in taste and flavor among different coffee can be subtle, so it’s important to evaluate them by tasting them under consistent conditions and isolating the difference to just the coffee bean.

Thus, whenever employing the coffee Cupping method a number of rigorous testing protocols are typically in place to ensure consistency during the assessment.

Traditionally the same size (170g - 255g) cup is used, and it will contain roughly 7-8 grams of coffee mixed with ⅔ of a cup of water.

The coffee will need to be lightly roasted and ground coarsely.

One key protocol is that the coffee should have been roasted within 24 hrs and then left to rest for at least eight hours after.

The coffee beans, once they reach room temperature, need to be stored in airtight containers.

Shortly before the cupping starts the coffee should be ground. In fact after the coffee is ground it should be tested within 15 min.

The water needs to be heated to 93 to 95°C, and the coffee should be allowed to steep in it for three to five minutes.

Coffee Cupping Testing

The first step in testing is to breathe in the aromatics - this should be accomplished by the tester placing their nose close to the cup, breathing in the aroma and analyzing the various notes and attributes.

The next step is tasting. Usually this involves drinking a spoonful of coffee while breathing in to determine both the taste and the aroma.

Once finished, the spoon needs to be completely rinsed with clean water and the next sample of coffee is tested in the same way.

When comparing the coffees through the Cupping method the following qualities and attributes (among others not listed) are analyzed:


  • Acidity
  • Aftertaste
  • Aroma
  • Balance
  • Body
  • Sweetness


Once the tasting and comparison are done often the tester will be offered a view of the roasted bean in a whole state so that they can comment on the appearance.

This step is saved for last to ensure the appearance of the bean does not in some way bias the tester to attribute notes and flavor qualities that might not actually exist.

Did You Know?

Sunalini Menon, a coffee quality control expert with a Master's degree in food and nutrition is known as Asia’s first woman professional in the field of coffee cupping.

“There are many relationships that I have built over coffee and I think that is the beauty of it. Coffee is not only my bread and butter, it not only energises me and builds my creativity, but most importantly for me, it has built a bond of a lifetime friendship, with people from across the globe.

Coffee is delicious, stimulating and most importantly a lovable drink. Coffee may look black as hell, but it is the most beautiful and delicious and, not to forget, the most romantic beverage.”


What is Strecker degradation in food?

Named after German chemist Adolph Strecker, the Strecker degradation is a chemical reaction which converts amino acids' into “aldehydes”, which are a potent class of flavor chemicals.


Why is coffee Slurped when Cupping?

The purpose of slurping the coffee when cupping is to aerate it and ensure it spreads across the full volume of your tongue and palate. Slurping helps ensure that both your taste buds and your nose are exposed to the taste and aroma of the coffee which gives you a more complete sense of the flavor.


How much trigonelline is in coffee?

Very small amounts of trigonelline are present in coffee beans, roughly 1% of the total bean weight. That said, it is found is much much smaller quantities in most other foods.