How is coffee aroma created?

Usually, the first thing that people do when they drink coffee is to take a big whiff of that delicious aroma. And sometimes, even the slightest smell of coffee can brighten up our day.

Most of us understand coffee aroma as the smell of coffee. However, coffee aroma is more than just molecules sensed by receptors in our nose. They contribute extensively to the overall coffee experience. Coffee aroma combined with mouthfeel and taste (sweet, sour, bitter, salty) perceived by the tongue, gives rise to flavour which provides a complex yet enjoyable experience to coffee drinkers. 

Curious about what creates this amazing smell that we all love? Read on to understand more about the way we perceive aroma, the chemical composition of aroma and how they are formed from roasting.

 

How do we “smell coffee”?

Simply put, there are two different mechanisms which are used to perceive aroma: orthonasal olfaction and retronasal olfaction. 

  • Orthonasal: smelling coffee through the nose 
  • Retronasal: when aromatic compounds are detected as they drift upwards through our nasal passage when coffee is consumed or when it is present in our mouth.

Coffee flavour cannot be achieved without the presence of aroma. When you have a cold, your food tastes bland because your sense of smell is compromised and flavours cannot be perceived. The same analogy can be applied here too. This is why aroma, taste and flavour are usually perceived together. 

What is coffee aroma?

When green beans are roasted, more than 800 volatile aromatic compounds are produced. Coffee aroma as we know of is a small proportion of such volatile compounds which we sense through our olfactory system. 

Although there are more than 800 aromatic compounds in coffee, many research asserts that only 25-35 volatile compounds contribute to coffee aroma, particularly those with high concentration and low odour threshold (the minimum concentration of chemical compounds detectable by the human nose).

Some major contributing families of compounds include:

  • Furans, which has caramel-like notes, is formed as a result of caramelization of sugar (a form of pyrolysis). 
  • Pyrazines such as 2-isobutyl-3-methoxypyrazine and 2-ethyl-3, 5-dimethylpyrazine contribute to earthy and toasty aromas.
  • Organic compounds like aldehydes formed by Strecker degradation, offer floral-like notes.
  • Sulfur-containing compounds, such as 2-furfurylthiol, give a “roasted coffee” aroma.
  • Phenolic compounds like guaiacol, which is a by-product of phenol degradation, provides smoky and spicy aromas.

Formation of coffee aroma

Green beans have no distinguishable smell and its aroma only arises when they are roasted. According to research, a large number of chemical precursors such as sugars, proteins, carbohydrates and chlorogenic acids, are present in green coffee. The concentration of chemical precursors varies in green coffee as it depends on many different factors such as varietal, growing conditions and processing methods. 

During the roasting process, the chemical precursors undergo a series of chemical processes where aromatic compounds are formed. According to a published paper on coffee flavour, some major chemical reactions include: Maillard reaction, Strecker degradation, breakdown of individual amino acids such as sulphur amino acids and hydroxy-amino acids, degradation of trigonelline, quinic acid moiety and pigments, minor lipid degradation and interaction between intermediate decomposition products.

As such, roasting is extremely complex as it puts the beans through a chain of reactions to produce various aromatic compounds. Different roasting levels will create distinct aroma profiles in a cup of coffee.

The Specialty Coffee Association (SCA) has classified aromas into three broad categories: enzymatic, dry distillation and sugar browning. 

1. Enzymatic aromas

- created as by-products of enzyme reactions in coffee beans during growth and processing
- common descriptors are fruity, flowery and herby

2. Dry distillation aromas 

- produced when plant fibers are burned during roasting 
- usually described as carbony, spicy, and woody

3. Sugar browning aromas 

- develop as a result of Maillard reaction during roasting
- commonly described as caramelly, chocolaty, and nutty

    Conclusion

    In short, coffee aroma is formed through a series of complex chemical reactions and plays a crucial role in our coffee drinking experience. Without aroma, coffee will taste bland and the experience will probably not be as enjoyable and satisfying.

    At First Crack Coffee Roastery, we carefully roast our beans to perfection. Our flavourful and aroma-rich coffee will guarantee satisfaction to your taste buds and to every smell receptors in your nose.

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