The complete guide about roasting coffee: Coffee roasting consists of heating green coffee so that it changes color, turns brown, and becomes edible.
Our article today it is for the beginners and professionals, you will find the complete guide about roasting coffee, What is roasting coffee beans? how coffee beans are roasted with a simple guide step by step, and how long are coffee beans roasted for? The color, the taste, the storage, and more.
Reading time: 10 min
The green coffee beans, have no smell and are impossible to grind, they are hard as stone! With roasting, the coffee will swell, change color and lighten to finally become edible, in the end, you can even bite into it!
This delicate roasting stage develops some 700 volatile components and aromas found in coffee. When the coffee begins to brown, proteins mix with the caramelizing sugars, causing the beans to brown.
We’ll take a look at:
- 1 What is roasting coffee beans?
- 2 How coffee beans are roasted, and how long are coffee beans roasted for
- 3 why coffee beans are roasted, and how to roast coffee beans without a roaster
- 4 Roast color, what should roasted coffee beans look like?
- 5 How to roast coffee beans professionally? The main stages of coffee roasting
- 6 How to roast coffee beans in a popcorn popper
What is roasting coffee beans?
Roasting is cooking raw coffee. To bring the coffee from room temperature to over 200°C and sometimes over 230°C, the craftsman uses a machine, the roaster, his senses, his experience, his knowledge, and, finally, measuring tools.
Roasting is a complex chemical phenomenon combining several transfers (heat, water, and mass) and pressure differences. When heated, the water in the coffee beans, which is 10-12% moisture, evaporates.
A flow of water thus goes from the heart of the bean to the outside. Also, this heating creates a flow of thermal energy from the outside to the inside of the bean. Roasting is therefore characterized by a double, contradictory flow – triple if we also consider the gas exchanges that take place from the inside to the outside.
These flows flow through dense material, the bean. They are slowed down by its structure, particularly the cell walls. As water passes from the liquid state to the vapor state, the pressure rises until all the cell walls are ruptured, thus definitively releasing all the oils present in the grain.
The transformation of the bean during roasting is therefore important and violent: it changes color, going from green to brown, loses up to 18% of its weight, doubles in volume, becomes less dense, more porous, and alternates the phases of endo and exothermicity.
The coffee bean, therefore, experiences a kind of Big Bang. Finally, roasting is fast, between 1 minute 30 minutes for industrial roasts, which we will not talk about here because they are too specific, and about fifteen minutes for artisanal roasts.
How coffee beans are roasted, and how long are coffee beans roasted for
Toasting coffee means subjecting it to a process in which the beans are brought to high temperatures, up to 200-220°C. Roasting is a real art because the coffee bean undergoes the toasting process and undergoes a series of chemical reactions that release its taste.
In the first case, large companies adopt a continuous process, with rotating drums heated by hot air, active all day long. Smaller companies, on the other hand, do the so-called “charge” roasting: they roast the beans when needed and for small portions.
While industrial plants have a very short roasting time of about 2 minutes at temperatures up to 500°C, smaller plants usually use a process of 20 minutes per 60 kg of product at a time, up to a maximum of 220°C.
The coffee in the latter case is often sweeter, less acidic, and with a full and strong taste. In both cases, the different degrees of roasting will enhance the peculiarities of the single coffee blend.
how to know when coffee beans are roasted
What if we wanted to try it at home? If you are curious about the idea, you can repeat the roasting mechanism in a small way even at home, using a heat source that can be the stove or the oven.
You have to observe and decide how long you want to keep the raw coffee beans on the stove. Check the color of the beans: as they absorb the heat, they will change from green to darker and darker brown. The darker the bean on the outside, the more full-bodied it will taste.
To toast the coffee, the oven temperature must reach 230°C and the beans must be placed in a single layer, on a baking tray. Roasting should last on average 15-20 minutes, with the same attention to the browning color.
why coffee beans are roasted, and how to roast coffee beans without a roaster
Roasting coffee at home allows you to taste different varieties or blends, especially those that normal consumers do not have available because they are difficult to find, even in the best bars.
It also represents a journey into the fascinating world of coffee, to the exotic countries where it grows and is produced, and gives the possibility to serve something unique to family and friends.
Roasting coffee at home is simple and suitable for everyone.
The roasting of coffee allows you to obtain herbaceous, acidic, and dry flavors or soft, round, full-bodied, and sweet-sour. Optically, roasted coffee beans can vary from light brown with a dry surface to dark brown with an oily surface, to black with a greasy appearance.
Traditionally, the level of roasting varies depending on the color, from the lighter English and American style to European: Viennese, French and Italian. It is difficult to determine the roasting level suitable for each type of coffee: the best and most fascinating thing to do is to try different styles and choose the one you prefer.
The roasting phases
After the first few minutes, the beans give off a slightly herbaceous aroma. The color gradually changes from grey-green to golden brown and a delicious fragrance of caramel and coffee pervades the air.
When the beans turn brown and begin to crackle, as the coffee aroma intensifies, the pyrolysis (internal transformation of the beans) is over; at the same time, their volume increases. From this moment on, the roasting process must be continued until the desired bean color is obtained.
As soon as the beans reach the desired color, it is necessary to cool them by spreading them on a tray (if a roasting machine is used, this will include a cooling phase).
The cooling phase should be accelerated by blowing on the beans to remove the skin; an alternative method to cool them is to spray a small amount of water on them. It is very important to cool the beans because the internal heat would continue to roast them.
The coffee reaches its maximum aroma 1 or 2 days after roasting, but it is delicious even after only 4 hours.
How to roast coffee at home
The simplest approach is to pour the green coffee beans into a large saucepan, turn on the gas and stir until they turn brown. This is the oldest and most traditional method of roasting, still used in many non-industrialized countries, although it does not ensure a homogeneous result.
Better methods are those using electric or gas ovens or roasting machines specific for coffee.
Roast color, what should roasted coffee beans look like?
Roasting is the high-temperature cooking of the green coffee bean. It’s art! Roasting acts as a revealer of the bean’s aromas. Without proper roasting, the specificity of the bean loses its luster.
There are several methods, but here’s what you need to remember: if the roasting degree is not high enough, the coffee may be too acidic. Conversely, over-roasted coffee will reveal too much bitterness.
Therefore, a so-called light roast (the beans are light brown), is generally more suitable for filter extractions, also known as slow coffee or mild methods. The coffee will rather offer acidulous notes of fruits and citrus fruits.
A medium to dark roast will be more suitable for espresso machines or traditional manual coffee machines. Too light an espresso roast will be too acidic.
For fans of Italian espresso, always prefer a darker roast that will reveal more gourmet notes of cocoa or toast.
A simple guide about coffee beans color:
The roasting time is based on the color of the beans. You will start with green beans, but during the roasting process your beans will take on different colors. Keep in mind that the darker the bean, the stronger the aroma of the coffee will be
Light brown: This color should generally be avoided, as it can result in a bitter taste. The coffee will have little body, little aroma, and little sweetness.
Medium-light brown: This roasting is common in the eastern United States. The coffee will have full body and aroma and intermediate sweetness.
Medium Brown: This roast is common in the western United States. It has a full-body, strong aroma, and medium sweetness.
Medium Dark Brown: This roast is also known as a light French or Viennese roast. The coffee has a very full body, a strong aroma, but the coffee is still very mild.
Dark brown: this coffee is then known as espresso or “French”. The coffee has a full body, medium aroma, and full sweetness.
Very dark (almost black): coffee roasted in this way is known as “Spanish coffee” or “dark French”. It has a weak body, medium aroma, and slight sweetness.
How to roast coffee beans professionally? The main stages of coffee roasting
Thermal shock: the green coffee is immersed in the roaster drum heated between 160 and 220°C. The coffee then undergoes a thermal shock of 150 to 200°C. The mass of green coffee at room temperature (around 20°C) causes the internal temperature of the roaster to drop for a few minutes until it reaches the lowest point (turning point) of around 80-90°C. It is therefore the bean that cools the drum.
Drying: from this low point, the heat transfer is reversed and the actual roasting begins. The coffee then begins to store heat, which gradually heats the water it contains, which soon gradually evaporates.
As the water migrates to the surface of the bean, the green color of the bean becomes more intense, vegetal aromas of cut grass become apparent, the ambient humidity increases and the bean begins to swell as a result of the increasing internal pressure. The drying of the grain is then significant and lasts at least until the first crack.
The rise in temperature: drying and cooking of the coffee follow their course and the first compounds are formed under the effect of the Maillard reaction, common to many products.
The beans change color, going from straw yellow to creamy orange, and swell. Complex aromas appear: bread, yeast, straw, beer, foie gras, and gases, such as carbon dioxide, are formed and begin to migrate outwards.
Caramelization: from around 170°C, caramelization begins in turn. The sugars are broken down, the grain turns brown and marbled, the production of carbon dioxide increases, and thus the internal pressure, and finally roast, toasted, caramel, and dried fruit aromas appear.
The aromatic maximum: between 180 and 200 °C, the aromatic maximum is revealed. The grains are then brown, veined with canals, the silvery film begins to dissociate, announcing the first crack.
The first crack: it occurs around 205 °C. The grains, which have now lost all their water, suddenly release part of their carbon dioxide. They literally “explode” like a popcorn or a chestnut forgotten in the embers. They double in volume, definitively blow out their silvery film, and their central groove widens.
The heart of the roasting process (development time): the crucial phase for the roaster begins, that of development. In less than three minutes, the beans will brown more and more, bulge, open in the middle, and bring the oils to the surface.
The acidity, then the aromas, the body, and finally the bitterness develops in practically successive waves. The roaster is then the only one to decide when to take the coffee out of the drum to stop the cooking. This can be during, just after or a few minutes after the first crack.
The second crack occurs around 225 °C. It is cellular. The beans, completely dry but still full of oil, continue to increase their internal pressure due to the heating of the oils, which causes the walls of their cells, weakened by the cooking process, to explode definitively.
All the oils are then released and come to burn on the surface. This is what gives these aromas, then dominant, of roasting (vanilla, coffee) and burning, or even carbonized. Specialty coffee roasters never roast up to this stage.
Cooling: the beans are finally taken out of the drum and cooled rapidly (> 3 to 5 minutes) in a tank where cold air circulates. From a certain volume, the coffee is wetted by sprinkling, just as vegetables are iced in restaurants to keep them crunchy and colorful.
How to roast coffee beans in a popcorn popper
COFFEE beans roasted with the popcorn machine: for a gas roast, it is best to use a popcorn popper. The best ones are the crank machines, which you can find in flea markets or on the Internet. The coffee roasted in this way will be deeper and more full-bodied, but the light notes and aromas of the coffee will be blurred.
Step of roasting the coffee beans in a popcorn.
- Place the popcorn machine, empty, on the gas stove. Set the heat to medium so that the temperature of the machine is about 230 °C. If possible, use a confectionery or frying thermometer to monitor the temperature of the popcorn machine.
If you do not have a popcorn popper and do not want to buy one, you can use a large skillet or saucepan. Make sure that it is perfectly clean or the coffee beans could soak up the taste of what you have cooked in the pan previously.
- Pour in the coffee beans. Only roast about 200 g of coffee beans at a time. Replace the lid of the popcorn machine and start turning the crank. You will need to keep stirring constantly so that your beans are evenly roasted.
If you are using a pan or saucepan, you will also need to stir constantly, as the beans are much more likely to burn in a pan or saucepan than in a popcorn machine.
- Listen to the crackling sounds. After about 4 minutes (although it can take up to 7 minutes) you should start to hear crackling: the coffee beans start to toast.
At the same time, the beans will begin to give off a coffee-smelling smoke that can be very powerful. Turn on your range hood and open a window to let the smoke escape. Notice when the beans start to crackle.
Regularly monitor the color of the beans. After the crackling starts, wait a minute and then start monitoring the color of the beans. When the coffee beans have reached the color you want, pour them into a metal strainer and stir them until they have cooled.