Physical changes of coffee beans during roasting
Before coffee reaches our cups, it goes through a series of procedures, ranging from harvesting to the roast, this last being one of the most important steps. Since, because it is a physical - chemical process, it is capable of defining the quality of the drink and the preparation method.
depending on the roasting curve, the grains begin to change their hue, they can even develop a variety of flavors. This is because the initial characteristics of the green beans are altered, starting with acidity, flavor balance and body. The latter will depend on both the roaster and the customer's preferences.
There are many questions regarding the physical changes of the beans when they are roasted. That is why, through this article, we will provide all the necessary information and you can share it with your friends or future colleagues in the coffee world.
Roasting, what exactly is it?
When we put the last cherry on the cake or put cocoa powder in some of our drinks, we observed that they were final details to achieve a good result. The same thing happens with roasting, which is the main thing in determining the quality of the coffee.
Of course, we cannot ignore factors such as altitude, origin, processing process, type of grinding, to name a few.
Basically, roasting is carried out using roasting machines, capable of providing heat to the green beans and those shades that range from tan to a darker brown.
When the coffee is subjected to this process, the organoleptic properties (the flavor, aroma, balance, to name a few) qualities that are part of a quality cup.
It should be noted that this begins by drying the moisture of the grains, which is around 12%. Another interesting fact that cannot go unnoticed is that coffee gains 100% volume. This also reduces your weight between 12 and 20% and loses 10% of your caffeine level, as well as decreasing your acids and a small increase in fat.
What physical changes do coffee beans undergo?
As we pointed out a few paragraphs above, the beans change color during roasting, losing moisture and weight. They also expand and even double their volume.
Shortly, we will explain in detail about each of the physical changes that are detected in the grains as a result of this process.
Color change of coffee beans
During the roasting process, coffee beans turn from green to yellow, from light to dark brown, and from darker brown to black. Normally, most roasters differentiate their roast level by color. However, there is no global consensus that defines or determines exactly the different degrees of roasting.
For example, a light roast for us, it can be a means for others. To have a little more consistency, we have based ourselves on the definition used Scott Rao in his book, The Coffee Roaster's Companion, Although this does not mean that it is the only one, nor the best.
In short, a light roast will have a more pronounced acidity and we can find more floral and fruity notes. The aroma will be more delicate, but will have less body than higher roasts. On the other hand, dark roasts develop smoky aromas, are more bitter and have charcoal notes. And if the roasts are too high, the flavors that will predominate will be burned, and in these phases the body of the coffee plummets.
roasting levels
In the roasting process we will define what we want to predominate before starting. This will be very different depending on whether we want the acidity, the body to stand out, or whether we want a point where most of the attributes are balanced.
First grade roast
According to what is defined by Scott Roa in his book, it is a Cinnamon or Cinnamon roast. Normally these are coffees that have been taken right at the beginning of the first crack.
These types of roasts have high, even pungent acidity. The notes that will predominate are herbal, sometimes the flavor is very similar to that of peanut. As for the body, it turns out to be very light. These coffees lose less weight because they still have a relatively high percentage of moisture. There are very few roasters that offer this degree of roastingIn fact, we believe that the beans are not given enough time to develop their potential.
Roast City
In this case, the grains are removed towards the end of the first crack. This type of coffee has a high and bright acidity, but more balanced than in the previous state. If you know how to develop it well, the result will be a sweet, juicy cup, with aromas of fruits, flowers and a touch of caramel.
Regarding the body, it will continue to be light. But if the roast is not done well, it would result in a coffee with herbal or even sour notes. We advise you that if they are well developed they can be good roasts for filter coffees, although this could be a topic of debate.
If you look on the website of a local roaster store that offers light roast beans, it is usually this type.
In Incapto Coffee, the degree of roasting we use for our beans is the Full City. Which consists of taking out the coffee just before the second crack begins. Let's say that this is one of the most balanced, since we achieve moderate acidity, the body is medium. As well as we also find notes of caramel and ripe fruit.
Viennese roast
Here the coffee is taken out right at the beginning of the second crack. Because, by that time the oils begin to migrate to the surface. The flavor of this type of roast is also caramelized. More bitter notes also appear and the body is at its maximum exponent.
Let's say that this type of roast is one of the most common, but surely we begin to hide the maximum potential that a coffee can have. Well, the aromatic and gustatory components begin to degrade. Thanks to this, you can get an extraordinary and exceptional coffee, because it will be differentiated from the rest by its bitter touches and by having a lot of body.
French roast
It is when the grains are removed a little later. At this point, bittersweet and bitter flavors predominate, as well as notes of charcoal or smoke. If we talk about the body, it has surely already started to fall. At this point, it becomes quite difficult to notice the true personality of a coffee.
Italian roast
It is necessary to clarify that, in Italy, there is not one type of roasting produced. In fact, most Italian roasters brew coffee in medium roasts. However, it is still not well known why very high and oily roasts are known as Italian roast.
In these roasts, the cellulose of the bean degrades a lot and this causes the coffee to go rancid quickly, because the oxidation process is accelerated. Well, as you might imagine, it has more burnt, smoke and charcoal notes. Even rancid notes, while the body is medium. Because it has declined more than in the previous case.
What other changes can we observe during coffee roasting?
In the roasting process, structural changes can also be observed. This is because steam and CO2 are generated, helping to increase the pressure inside the grain. This forces the grain structure to expand and grow. Well, when the grain can no longer grow, the cellulose cracks, releasing the steam and gases that have been generated inside.
It is at this moment when the first crack noise occurs, similar to the one we hear when we make popcorn in the toaster. That same noise is what gives its name to this critical point of roasting.
Light to medium roasts will be taken out between the first crack and before reaching the second. While the media, it will be from a little before the second crack, in fact a few seconds after.
In the case of the second crack, what predominates in the expansion is the accumulation of C02, since the free moisture could evaporate before reaching the first crack.
To give you an idea, take out the coffee 30 seconds before or after can make a substantial change in the outcome of the cup.
Another important aspect is the development of the internal part of the grain. Let's say it's like cooking anything else. Depending on the process you do, you can leave it raw on the inside and burn it on the outside. Or simply cook inside and out very similar to the previous one.
In order not to take advantage of the coffee's potential, it is advisable to leave it at its optimal point inside giving good development to the grain and removing it at the right time.
As we said at the beginning, coffee loses weight, and depending on the type of roasting we do, as well as the initial humidity of the bean, between 12% and 25% of weight can be lost. This is what we consider the roast loss.
Finally, due to the expansion that we have mentioned previously, during the first and second crack, coffee can grow between 150% and 190% of its initial size.
This is a whole class on the physical changes of coffee beans during roasting. A procedure that if carried out perfectly we would have an exquisite drink, with which we could delight ourselves for hours and make the mornings the most pleasant time of the day.
