Where does the flavor and aroma of coffee come from?

A coffee bean is a mysterious micro-world of aromas and flavors encapsulated in a structure that first glance looks simple.

How to extract all those wonderful substances from the coffee bean
and enjoy them in a cup?

I invite you to continue reading this post, where I share some curiosities about the origin of the aroma and flavor of the coffee.

Chemical composition of unroasted Arabica coffee bean (4).jpg

Source

cintillo atardecer definitivo.png

A cup of coffee is composed of two types of molecules. Molecules are soluble in water, which gives coffee its characteristic flavor, and the volatile molecules give its delicious aroma. However, to activate these molecules, it is necessary to provoke a series of chemical reactions to be able to enjoy them.

A green coffee bean has many molecules. The presence of these molecules depends on several factors, such as the type of bean (Arabica, Robusta), the area and climate of cultivation, and the method of harvesting and storage. But broadly speaking, they are macromolecules that are part of the pattern of their chemical composition. To exemplify this, I present below a scheme of the chemical composition of a green coffee bean (unroasted) of the Arabica type since it is a coffee with high cultivation and demand by consumers.

Chemical composition of unroasted Arabica coffee bean.jpg

Elaborated by the author
Data´s source

The unroasted green coffee bean does not possess sensory attributes that can be enjoyed instantly. Their flavor is acidic and astringent, and the aroma is herbal. Nothing like that dark elixir we enjoy in a cup. However, each molecule found inside the coffee bean will fulfill a function in the attributes of a good cup of coffee such as aroma, flavor, aftertaste, and body. These are the fundamental attributes that are considered when evaluating a cup of coffee.

To activate all these substances the coffee beans must go through a series of processes. The bean must be extracted from the pulp, and later the parts that are still adhered to the bean must be eliminated. However, the most important procedure is roasting, which should be carried out carefully to extract the best attributes from the coffee.

cintillo atardecer definitivo.png

When the coffee is roasted changes occur in its structure that favors its subsequent grinding and filtration. As we can observe in the following graph, the coffee bean loses a percentage of water due to the effect of the high temperatures. The carbohydrates decreases because many of them are transformed into sugars that caramelize and give the characteristic color of roasted coffee. The percentage of lipids and proteins increases due to the loss of humidity. Their content becomes even more concentrated in the bean, which will favor the generation of aromas and flavor in the cup of coffee.

Chemical composition of unroasted Arabica coffee bean (3).jpg

Elaborated by the author
Data´s source

To roast coffee beans, temperatures above 170ºC are necessary to activate the amino acids of the proteins of the coffee beans and their sugars (carbohydrates). This activation between these molecules in the presence of heat gives way to a series of chemical reactions. They receive the name of Maillard Reaction, responsible for the aroma and flavor of the coffee.

Chemical composition of unroasted Arabica coffee bean.gif

Elaborated by the author

However, depending on the temperature and the time of exposure of the coffee bean to heat, different degrees of roasting will be obtained. Generally, three degrees of roasting are considered: light, medium, and dark. The coffee roasting guide subdivides these types of roasting into many others, but for the pedagogical purposes of this post, I will only use the basic classification.

Chemical composition of unroasted Arabica coffee bean (5).jpg

Elaborated by the author
Source

To achieve adequate roasting, the coffee beans must be exposed to a constant temperature. Depending on the type of roasting desired, the time of the process can vary from 8 to 32 minutes.

cintillo atardecer definitivo.png

When the roasting of the coffee is light, the beans are exposed to temperatures between 170 and 200ºC for 8 minutes. This gives the beans a golden color similar to honey. The glucose and fructose of the beans begin to caramelize. It is why we can perceive a sweet aroma. However, this temperature and exposure time is not sufficient to transform the acids contained in the coffee bean. Therefore the flavor of the infusion will be acidic with herbal and citric tones. In this type of roasting, the pH of the coffee bean continues to be acidic which prevents the solubilization in the water of some of the substances responsible for the body of the coffee. Likewise, the typical bitter taste is not perceived since the chlorogenic acids present in the coffee bean have not yet degraded.

Chemical composition of unroasted Arabica coffee bean (4).gif

Elaborated by the author
Source

cintillo atardecer definitivo.png

As the degree of roasting increases the sensory attributes of coffee change. When we prepare a cup with medium roast coffee there is an explosion of intense flavors and aromas. Medium roast coffee beans are those that are exposed to 205ºC for 8-10 minutes. This temperature causes the coffee to lose humidity. While the roasting process is taking place, water vapor is formed inside the bean which tries to escape to the outside, which is why you can hear crackling sounds like those made by popcorn. It is a very curious sound. As the grain loses moisture it expands. It can almost double in size, but it also loses weight. In medium roasting, it is estimated that the weight loss is 12% to 14%. The loss of humidity makes it easier for the molecules to react with each other, which is why the color of the coffee is brown, and the flavor is bitter since the chlorogenic acids degrade to form quinic acid, which gives it its deliciously bitter taste. The pH of the coffee bean becomes neutral and allows the caffeine to solubilize in the water giving body to the infusion. The exposure of the coffee bean above 200ºC allows the sugars and amino acids to combine perfectly to provide roasted nutty aromas and volatilize the essential oils. Just describing this makes me want to go grab a cup of coffee 🤣🤣🤣

Chemical composition of unroasted Arabica coffee bean (5).gif

Elaborated by the author
Source

cintillo atardecer definitivo.png

When we prepare a cup of coffee with dark roasted coffee, we obtain a coffee with a pronounced flavor and aroma. The coffee has been roasted for almost half an hour at a constant temperature of 225ºC. It is a temperature and time limit because above this temperature and time, the aromatic and sapid properties of the coffee deteriorate. When the coffee beans are exposed to 225ºC, the essential oils are exhaled to the outside of the bean through the vein (central cleft) lubricating the bean and giving it a shiny appearance. As is to be expected these lipid molecules are very sensitive to degradation by the environmental oxygen. Therefore it is recommended to buy dark roasted coffee in small presentations for its rapid consumption to avoid the oxidation of the essential oils that can confer a rancid or old wood flavor to the coffee. In this roasting the humidity lost is almost 20%, an aspect that influences the selling price. The greater the loss of product, higher price.

Making a cup of coffee with this type of roasting produces aromas of roasted wood, and its bitterness is more intense. Even the release of essential oils is so high that we can appreciate it as a small halo of oil in our cup of coffee, which gives a robust body to the liquid.

Chemical composition of unroasted Arabica coffee bean (6).gif

Elaborated by the author
Source

cintillo atardecer definitivo.png

As you have been able to read, all the attributes of coffee that drive our sense of smell and taste crazy are the result of the chemical magic that the heat provokes in the coffee beans when they are roasted. Depending on the degree of roasting, the sensory experience will change.

To enjoy to the maximum the aromas and flavor of coffee in addition to the type of roasting, we should take into account other aspects such as:

Type of coffee bean (Arabica, Robusta).
Storage conditions in the store
Storage conditions at home
Grinding
Filtering mechanism to be used

image.png

Source

If you take into account all these aspects, I assure you that your experience with coffee every day will be more mind-blowing.

Thanks for reading. See you in a future post!

cintillo atardecer definitivo.png

Link consulted:
Nose Dive: A Field Guide to the World's Smells

The Relationship Between Time and Color in Coffee Roasting

Coffee Roast Guide

cintillo atardecer definitivo.png

English (2).gif



0
0
0.000
15 comments
avatar

Que buena información, no tenía idea. Gracias por compartir!

0
0
0.000
avatar

Me alegra que lo hayas disfrutado. Muchas gracias por pasar por aquí! ☕️

0
0
0.000
avatar

Very interesting post. There is so much science involved in aroma and in roasting.

A_Virtual_Coffee_Shop-3.jpg

0
0
0.000
avatar

Hello @leaky20,

I love the message of your image:
"I will need a few cups of coffee to process all this information"...I laughed a lot!

Many foods go through some processes that we sometimes overlook. I hope this information is helpful when selecting which coffee to buy and what attributes to expect when brewing a cup of coffee.

Thank you very much for visiting my post! 😃☕️

0
0
0.000
avatar

@millycf1976 makes all of the images. She is quite good at it. They are all very funny.

I'll keep the info in mind when I buy coffee for sure.

0
0
0.000
avatar

That's great, you both make a great team!

0
0
0.000
avatar

All this information is very interesting, my friend. It is good to know it to take it into account when enjoying a coffee and recognizing its quality. Now, the experience of drinking coffee will be much better. Thank you for sharing your knowledge with us. Best regards.

0
0
0.000
avatar

Thank you for all this information. It made me want to have a nice cup of coffee.

0
0
0.000
avatar

Thanks for your contribution to the STEMsocial community. Feel free to join us on discord to get to know the rest of us!

Please consider delegating to the @stemsocial account (85% of the curation rewards are returned).

You may also include @stemsocial as a beneficiary of the rewards of this post to get a stronger support. 
 

0
0
0.000
avatar

It is as you say at the beginning of the publication:

*A coffee bean is a microworld".

I had no idea of all these processes so elaborate and so to speak, something magical, thanks for sharing :D

0
0
0.000