Bitterness is the peculiar sensory characteristic of coffee. But why is coffee bitter and why do we like this typically unpleasant taste in our favorite drink?
Roasting is the alchemy that transforms and blends while remaining mystical and magical.
It determines the unmistakable aroma and flavor typical of the unique beverage we universally call “coffee” which is a must for billions of people worldwide.
Had coffee plants been discovered during the European Middle Ages, it’s quite possible some coffee lover would have ended up at the stake like a witch!
Returning to modern alchemy, roasting is one of the fundamental stages in processing coffee beans.
It not only makes green coffee suitable for consumption, but it confers each coffee blend its own aromatic profile and organoleptic characteristics.
During roasting, applying heat to the beans induces transformations that produce highly complex components and aromas.
The roasting process
Roasting consists of adding heat to the coffee beans to increase, according to specific profiles, the temperature and the cooking time.
In the traditional roasting method, in a large rotating drum, the coffee beans are treated to a heat source which rises gradually to a temperature ranging between 200 and 230°C for about 12 to 15 (in some cases 20) minutes.
- Dry the beans at 100°C and they turn a golden color while the roasting fragrance starts to be released.
- As roasting continues from 150-180°C, the bean’s volume increases and becomes larger, shiny
and begins to turn a distinctive brown color.
- At 200-230°C the roasting reaches its optimum level and beans acquire their familiar rich, brown color while losing weight and becoming brittle. The coffee gains its distinctive scent. Beans experience a steady and necessary carbon dioxide loss for days after roasting.
For the most intense roasts, the absolute maximum is 240°C. Beyond this point, spontaneous combustion of coffee can occur.
The process must end at precisely the right time.
Over-roasting destroys essential, volatile aromatic compounds and upsets the ideal balance of acidity and bitterness.
That’s why, once it’s been extracted from the roaster, the coffee is quickly brought to room temperature by using air flows.
Roasting now complete, a critical, calibrated, air-cooling phase goes into effect to literally stop the beans from cooking, keeping aromas intact and preserving the blend at its best.
In SpecialCoffee the roasting process is done by convection with an “eco-friendly” technology.
“Eco-friendly” as thanks to heat recovery (the ability to recycle hot air produced) we produce less CO2 emissions.
By convection as, compared to traditional roasters (with a rotating drum and a flow of hot air from below), we roast by a flow of hot air through the roasting drum (and no more by direct contact with the hot surface).
The convection method distributes the heat more evenly over the beans, guaranteeing more uniform cooking, inside and out, and thus better developing and enhancing the coffee’s organoleptic properties.
Moreover, during the different phases of the roasting process, correct heat transfer to the beans facilitates the necessary chemical reactions (such as the all important Maillard reaction that transforms the sugars).
The roasting? Slow!
The traditional plodding way of processing is considered the only way to enhance the refined nature and complexity of superior coffee varieties.
To obtain refined aromas, it takes time and coffee is no exception to this rule.
If coffee is roasted too quickly, certain aromas will never develop. Never.
If you don’t allow the coffee to stand after roasting, certain aromas never develop. Never.
What happens during roasting?
Roasting is coffee’s version of high drama: 15 minutes is the critical time when some 800 substances emerge under heat and each contributes to the taste and aroma of the blend and to its very heritage.
During the delicate roasting stage, a metamorphosis occurs in the green beans. They change color, decrease in weight, increase in volume, lose moisture and, above all, acquire aroma.
Several initial characteristics disappear or are reduced and new ones emerge.
In the course of this process, coffee experiences major physical and chemical transformations.
Analyzing the chemical-physical transformations that the coffee bean undergoes when heat is applied (the roasting process) defines the roasting from the technical-scientific point of view.
We can summarize the main physical changes in the coffee bean as follow:
- weight loss by about 15 to 20% due to water and organic substances evaporation (as water is lost, the moisture content, which had hovered around 11%, drops to a mere 1%);
- volume increase from 40 up to 60% more than the raw product, due to the gas pressure formed inside the bean;
- different consistency of its structure, changing from hard and elastic and becoming rather crumbly and brittle, less dense and more porous;
- color going from green (of Arabica coffees or the brownish-yellow of the Robustas) to brown as the sugars are caramelized and the cellulose carbonized;
- moreover, during roasting, coffee beans lose their residual silver sheath which is more or less completely eliminated.
Chemical modifications regard the decrease of several components, such as sugars (the Maillard reaction, one of the most important, in which sugars in the coffee undergo pyrolysis and are transformed, caramelized), water (reduced by about ten times), chlorogenic acids and the trigonellines, the lowering of which makes the future espresso coffee easier to digest.
Caffeine content remains nearly unchanged and particular elements responsible for unpleasant odors in green coffee almost completely disappear.
At the same time, thanks to a process of pyrolysis (the internal transformation of the bean due to heat) and the interaction between various elements such as sugars and proteins, hundreds of different volatile composites begin to burst out with roasting to which we owe coffee’s special aroma.
The longer the roasting process, the greater the number of oil droplets that emerge on the surface of the bean and this is what determines the coffee’s specific aroma.. the same essential oils for the creation of the crema (but also the same oils that are deposited on the equipment).
Examining a coffee bean under the microscope:
- during the roasting phases you can see that the increase of pressure inside the cells (caused by the formation of gases like CO2, steam and other volatile substances) causes them to expand (as when a balloon is inflated) and creates real pores inside the bean;
- after a day of roasting, you can see the droplets of oil that tend to migrate on the surface of the coffee bean.
The roasting process’ influence in the cup
The roasting process determines the final taste and aroma in the cup and it shifts between two extreme critical points: the “underdevelopment” and the “baked”.
In the pursuit of the perfect cup, where the natural sweetness of coffee and the full aromatic fragrance is enhanced, a skilled roaster must firmly take the rudder in hand.
Otherwise, the risk is to have a coffee still vegetable, annoyingly acidic and astringent (the so-called “underdeveloped”) or on the contrary, have a flat coffee poorly aromatic (the “baked”).
According to the different degrees of roasting, with the same coffee blend, it is possible to produce a coffee with a herbaceous slightly sour taste, as opposed to a soft and velvety one, or with hints of fruit rather than an intense bitterness.
The darker the color of the coffee, the fewer the acid sensations and the more the bitter ones.
The quality and sensations offered by the different coffees in the cup can be influenced in many ways with the roasting profiles being one of these.
The same roasted coffee with different roasting profiles will give different results until almost unrecognizable.
It is extremely difficult to generalize the thousand variables that can be given by a different roasting profile.
What are the roasting profiles?
Initial temperature higher or quieter, slow roasting to preserve some aromas or quick to enhance the body of the coffee.. what are the roasting profiles in coffee roasting?
Roasting profiles are control systems which make it possible to manage the temperature and the timing of the roasting process. They vary according to the types of coffee being treated, as well as how the coffee will ultimately be extracted.
Coffee is a natural product with several species, various qualities or origins. When subject to heating of roasting, reacts differently depending on its own specific organoleptic and structural characteristics as well as its moisture content.
Robusta coffees need more energy and a longer roasting time even though a very long roasting is never desirable since it cooks the coffee rather than roasts it.
For Filter coffee, Syphon, Aeropress and French press, a light coffee is necessary which means a shorter roasting time in order to give the bean a light fragrance, rich in acid notes, and a low specific weight ideal for this type extraction.
For Moka and Espresso, a darker roasting is in order so that the beans take on a fuller body and a slight concentration of aromas, presenting a color tone called “monk’s tunic” in jargon that will be more or less evident depending on the type of clientele to which it will be destined (in Northern Italy, for example, they are more accustomed to a light and aromatic coffee, pleasantly acid while in the South, a more bitter, full-bodied and intense coffee).
For Ibrik (Turkish coffee) or in general for coffee where another extraction yield is required (therefore with a higher specific weight, high body and strong aroma) a light roast is always preferred, but carried out in a very slow time which will allow different transformations with the formation of more soluble substances.
Roasting and blending coffee beans is more than pure technical skill, it is a sheer art form.
At SpecialCoffee, we have developed the skills to fine-tune the roasting process according to the blend and based on the specific use, market and country where the coffee will be consumed.
How to become an expert roaster?
Roasting and tasting.
In a few other activities, the practice is so fundamental.
A very long training is required for gaining experience (clear that it will also be necessary to be good coffee tasters to evaluate the cup) and sensitivity to evaluate the color and nuances of the roasted coffee.
Hey barista, beware of too fresh coffee!
Have you ever opened a bag of coffee, poured it into the bell hopper of the grinder, started turning the beans into espresso cups and realized that the crema is not as you are used to seeing it (it must be persistent, with a very fine texture, a nice hazelnut color and possibly include beautiful “tiger stripes”)?
Have you ever had the crema more like a foam with big bubbles and the espresso that tends to drop dramatically in the cup leaving a ring of cream on the edge that opens inexorably in the middle?
The cause might just be too fresh a coffee, roasted for too little a time and not properly degassed.
In fact, during roasting, the coffee produces carbon dioxide which is important for the creation of the crema, but only in the right measure. For this reason, it must be at least 48 hours after roasting.
Coffee commands a rest period of a few days in order to give its best. For this reason, proper storage is paramount!