Blending before or after? Cooling by air or water? Degassing? The roaster's job is made up of details and choices which then make the coffee blends unique and of high quality.
Among the basic tastes, bitterness is the predominant flavor in roasted coffee beans.
It is the peculiar sensory characteristic of coffee, its typical taste, its signature.
But how is the bitterness of coffee created?
And why do we like such an unpleasant taste in our treasured coffee?
Let’s start from the end (the cup) and try to understand what happens in our mouth when we drink coffee and perceive the bitter taste.
First of all, let’s debunk a commonplace misconception regarding the perception of taste: the so-called “taste map”.
The custom of depicting the tongue as divided into four precise areas, where the sensitivity of the four basic tastes is more marked (sweetness at the tip of the tongue, sourness and saltiness at the sides and the bitterness at the terminal part) is now considered obsolete.
Actually, the taste buds do not focus sensitivity on any one taste, but we are able to perceive the basic tastes on the whole surface of the tongue because the fibers in the individual papillae provide a multi-faceted response to many different stimuli.
The thing that changes is the sensitivity in the various areas to the different tastes.
What is the bitterness?
Bitterness is the most complex of tastes, stimulated by a vast class of chemical compounds.
In the mutual interplay with other tastes, bitterness is masked by sweetness and reinforced by saltiness and sourness.
Bitterness is more perceptible than the other primary flavors and, above all, its persistence is quite pronounced.
Often perceived as unpleasant, presumably because many toxic natural substances have a bitter taste and therefore, at an evolutionary level, it is the taste that alerts us in case of ingestion of potentially dangerous substances for our body.
Why then is the bitterness of coffee irresistible?
How could we imagine a coffee without bitterness?
It is a fact that the perception of tastes evolves with growth and that a particular flavor is gradually more appreciable as we come into contact with it.
However, the mechanisms underlying these changes are not at all simple.
In the case of coffee there are physiological reasons mainly related to caffeine.
Precisely caffeine is at the basis of the mechanism called “flavor-consequence learning”. This mechanism explains why the effects deriving from the consumption of a food (in the case of coffee, the energy given by caffeine) are associated with its taste which, even if not pleasant, ends up being appreciated.
We have therefore developed ways to make us like foods that, in some way, give us benefits. We have learned to associate caffeine with positive effects of stimulation and well-being, and these body responses make us even more receptive to its characteristic aroma.
Why is coffee bitter?
By its nature, green coffee contains chemical compounds that have a pronounced bitter taste, such as caffeine and chlorogenic acids, and others that develop it after roasting.
Just think that the average caffeine content in Arabica is 1.2% and in Canephora 2.4%. And that, if the appellation “robusta” indicates its ability to adapt and resist dry climates and attacks from diseases and parasites, this ability is due precisely to its high percentage of caffeine which acts as a natural pesticide.
However, if we try an infusion of green coffee, we discover that the taste has little to do with what we usually associate with a cup of coffee.
The roasting is the process of transferring heat to the bean which triggers hundreds of chemical reactions, the most important of which are the Maillard and caramelisation reactions.
During the roasting process, the chemical composition of the bean is completely transformed especially with the creation of thousands of new volatile aromatic compounds.
The percentage of caffeine, on the other hand, remains unchanged, while the chlorogenic acids are modified, producing numerous by-products which remain bitter in taste.
With the Maillard reaction, through the chemical reaction between proteins and sugars, melanoidins are generated, another class of chemical compounds responsible for the bitter taste of coffee.
Finally, the same sugars, following caramelization, tend to become bitter if the roasting is too strong.
The intensity of the bitterness that can be perceived in a coffee is therefore the result of various factors, each of which has a variable weight according to the roasting.
As a general rule of the bean cooking process, increasing the degree of roasting leads to a decrease in acidity and an increase in bitterness.
The color of the bean can therefore be the first indicator that we can interpret: the darker it is, the greater the degree of roasting and the more intense the bitter taste in the drink.
Although roasting is the key element in determining bitterness in coffee, preparation and extraction also play their part.
If the grinding is too tight, the water/coffee contact surface increases and consequently the extraction capacity of the bitter compounds contained in the roasted coffee increases.
The same result occurs when the water temperature is too high.
Finally, there is the extraction time to consider: when the percolation is too long (over-extraction) an intense and unpleasant bitterness is evident since the water begins to extract chemical compounds which decrease the gustatory balance of the drink and make the coffee unbalanced on bitterness.
We cannot fail to mention the fact that many of us prefer bitter coffee, while others feel the need to mitigate this taste by adding sugar.
Explaining these differences with “it’s a matter of taste” is an understatement: in fact, it has long been known that there are individual differences in taste sensitivity, and these differences are particularly evident in the population for bitter and sweet, less so for salty and ‘acid.
The genetics of taste partly explain these differences. Therefore, it would not be the palate that determines the predilection for the bitter drink but rather a genetic variant related to the ability to metabolize caffeine, which is also found in people who choose dark chocolate over milk chocolate and smooth tea over sweetened tea.
The sensation of bitterness imparted by a bitter flavor is perceived within a certain range and becomes unpleasant when quite intense.
A high quality coffee is characterized by a balanced ratio of acidity and bitterness as well as a full aromatic fragrance.
With the declared aim of obtaining the perfect cup, only an experienced roaster knows how to develop roasting profiles that enhance the natural sweetness of the coffees and highlight an acidic note while avoiding an excessive development of bitter compounds.