Raw coffee VS roasted coffee: the chemical and physical differences

I maestri della tostatura media

We have already looked at raw coffee, its terroir, environment, plant, and possible defects. We have seen the differences between arabica and robusta, its organic varieties, the drupe and how it is processed and transported.

We then described roasted coffee, especially its aroma and extraction processes.

We have also already described the different levels of roasting!


Now let’s talk about the differences between raw and roasted coffee.

Raw coffee undergoing roasting undergoes chemical and physical changes. These are critical to being able to achieve the final product we all know.

If raw coffee were not roasted, it would be impossible to grind and thus impossible to prepare the beverage.

Raw coffee, as it is, does not allow us to achieve much. It is only through roasting that coffee really comes alive!

The chemical and physical changes

But back to us, the chemical and physical changes that raw coffee undergoes in roasting are:

  • Color change: from green to yellow, then cinnamon and finally brown;
  • Weight loss, 15% to 20%;
  • You halve the density;
  • Moisture loss from about 12% to about 1%;
  • Doubling the volume;
  • Up to a certain level of roasting you gain sweetness, after which you lose it;
  • Up to a certain level of roasting you gain body, after which you lose it;
  • As the roasting progresses acidity is lost in exchange for bitterness;
  • Development of more than 800 volatiles that make up the aroma;
  • Development of many gases, chief among them Carbon Dioxide (CO2), as well as water vapor and other substances.

But the key difference is that raw coffee is dense and firm, while roasted coffee is crumbly, thus grindable!

We understand better

Roasting is intended to promote aroma development while making the grain crumbly, ready to be ground.

We said that coffee changes color. In fact, it first changes from green to yellow, and here the roaster understands that the bean is “drying out,” that is, losing moisture.

After that it becomes cinnamon, it is then beginning the pyrolysis (decomposition) phase of sugars. At this stage the grain is developing its flavor profile and cellular weakening is occurring.

It is now in fact that in the roasting stage the 1st crack takes place.

Because the cell walls are weak and so many gases have formed inside the kernel that they begin to press on the same walls to escape, the crack, that is, a popping sound, very similar to popcorn, occurs.

Thus far, therefore, raw coffee has:
  • Lost moisture and therefore decreased density and also decreased weight;
  • It has changed color;
  • It has become crumbly;
  • It doubled in volume, thanks to the crackling;
  • He developed gas;
  • He developed the flavor profile.

This is followed by cooling, to stop the cooking and thus stabilize the chemical and physical characteristics achieved by the grains. In fact, the roaster has the ability to choose at what roast level he likes his coffee and “freeze” it at exactly that predetermined moment, like a photograph.

In these very few lines I have summarized much of the roasting process for you.

But don’t think that’s all there is to it!

Roasting is a very delicate and complicated process, which requires a roaster’s chemical/physical grounding in understanding every single change in the grains and how to modify or control the chemical reactions, in order to achieve the desired result!

Surely this article will be followed by many more articles on roasting and its steps.

For now, I will just anticipate that there are different levels of roasting, which will give different coffee results and therefore different drinks in the cup.

The 3 macro groups are:
  • Light roast: enhances the cooler, more acidic notes in coffee, but gives little body to the drink;
  • Medium roast, the one chosen by us at Caffè Ernani: it brings out all the merits of raw coffees, giving an intense and aromatic cup, along with a fresh acidity and good sweetness. A good cream and body is formed in espresso;
  • Dark roast: you can recognize it immediately by eye because the coffee is almost black. It gets this color because of the outermost layer practically burned off. So it is easy to see that this roasting, also called Italian-style, enhances bitterness and empyreumatic (burnt) hints.
Figuring out what type of roast you are consuming is easy! Just look at the grinder in the coffee shop or the coffee you bought and observe the color of the beans.

Many people, as a result of this discovery, ask me, “Why is it that if medium roast is the best roast, it is not used by everyone?”

I reply, “Because just as it enhances all the merits of raw coffee, it also enhances all the flaws!“.

In order to be able to afford to roast your coffee to an average level, you have to start with a quality, defect-free raw coffee.

It is easy to imagine how buying a high quality bean is more expensive than buying a low quality coffee.

But why do roasters buy coffee knowing that it is of low quality?

In our Italian tradition the 1€ cup still seems untouchable, although in the last period things are changing a bit. Therefore, to obtain a higher profit margin they opt for a defective grain. They then roast it so much and hide all the flaws from the consumer because of the strong hint of bitterness.

What happens next?

You pour a sachet of sugar into the cup and drink it all!

That is why a light or medium roast coffee is said to be drunk without sugar!

Because it does not have a strong bitterness, on the contrary! It expresses an incredible aromatic range, so it would be a shame to hide it with sugar taste!


Marketing, E-commerce e Social Media Manager
Coffee Lover


Martina Mazzoleni

Marketing, E-commerce e Social Media Manager Coffee Lover

Leave a comment

Your email address will not be published. Required fields are marked *

The reCAPTCHA verification period has expired. Please reload the page.

torna su
Apri chat
Bisogno di aiuto?
Ciao 👋
sono Martina, come ti possiamo aiutare?
Risponderò a qualsiasi tua domanda dal lunedì al venerdì, dalle 9.00 alle 18.00! ☕️💛