Roasted Coffee Facts
The Visual Aspect
Unlike other types of drinks, the visual evaluation of coffee is not based on its clarity, intensity or nuance. Nevertheless, its appearance can give useful information about the quality of the brand used and the skill of the person who prepared it. This explains why tools such as the cup and the goûte caffé, though lacking transparency, can show the most important characteristic of all: the crema.
The crema is tested according to:
- its color and, in particular, its intensity and its nuance;
- its persistence, i.e. the time it takes for the crema to break up.
The color of the crema comes mainly from sugar that has been caramelized during the roasting process, and partly from phenols that have been oxidized by the heat applied during the same process. The intensity and nuance of color can vary from deep hazel to dark brown with reddish shades and light hazel streaks, if the coffee has been prepared using an Arabica blend.
It can be pale hazel in the case of underextracted coffee, or mahogany in the case of overextracted coffee. If the coffee has been prepared using a Robusta, the crema is darker and has a grayish shade. The consistency of the crema is given by proteins, fat, sugar and by other viscous substances emulsified by gas during the preparation of coffee. The same components affect the duration of the crema i.e. the crema that remains in the inner part of the cup after the coffee has been drunk.
A good espresso coffee has a compact, fine-grained, long lasting crema and fine buttonhole. These characteristics are important because they are strictly related to the sensorial appreciation of high quality crema, and they are also vital to keep the aroma within the coffee until it is drunk.
The Aromatic Profile
During the sensorial evaluation of coffee, the comparison between the aroma and our olfactive sense is of paramount importance. This is easily explained. Coffee aroma is made up of some thousand molecules, which, according to their interaction, create sensorial maps. For the taster, such maps reveal important information about the origin of the beans that make up the blend, and about the skill of the person who prepared the drink.
Our olfactive sense is complex; a mucous membrane of a few square centimeters is able to recognize an infinite number of different molecules sending signals to the brain. If there is a weak spot, it is that our brains pay less and less attention to the signals sent by our olfactive organs. Our ability to retrieve olfactory signals is weaker than the one that allows us to retrieve images.
We are almost always able to retrieve an image, but the same can’t be said of a smell. For example, when you hear a person’s name, your brain will conjure up a picture of his/her physical appearance, which allows you to describe him/her in detail. We will only remember the name of a flower by its scent if the scent is present at the time.
Only through constant training can we store such information, the key to which will nevertheless remain outside ourselves. Not only is the aromatic profile hard to recognize, but it is extremely difficult to communicate. It has been likened to a badly tuned radio, broadcasting in a foreign language. In other words, the most important part of our sensorial analysis is also the most difficult to be measured objectively.
In the case of coffee, things are not any easier: over 800 types of molecules able to stimulate our olfactive sense are formed, first by the natural synthesis of the plant, then by the stages the green beans undergo before the final roasting. Each molecule carries a signal that, in combination with others, creates something completely new and always different.
If 26 letters of the alphabet allow us to write innumerable poems, and the world can write its music from 7 musical notes, how many different signals can 1000 active molecules carry? The olfactive organ is the only one called to work twice: once during the direct act of smelling, and again after swallowing the drink through the back of the throat (the aftertaste).
What is the difference?
In the first case, the molecules, which are more volatile because of the high temperature, reach the mucous gland in the nasal septum. By becoming soluble in the mucus, they stimulate the receptors. The taste common to all types of coffee is that of the roasting; only afterwards can we detect the characteristics of a good blend and expert preparation.
After swallowing our sip of coffee, its temperature decreases to that of the human body. Consequently, we would expect our perception of the aroma to be reduced, but two phenomena change this. First, the espresso settles on the oral mucus, which increases the evaporating surface and enables us to better segment the taste. Secondly, the fat present in coffee makes this process last for a long time, which allows the taster to carry out a detailed examination, and the consumer to enjoy the taste of this drink after swallowing it. All this is possible because the aromatic components reach the olfactive mucous through the back of the throat.
When we directly smelling coffee, we evaluate the intensity and degree of the aroma (the amount of positive and negative odors); the intensity of the roast that typifies the various degrees of roasting; and the fineness or preciousness of the fragrance. We evaluate negative and positive odors through the back of the throat.
The negative odors are caused by faults in the green coffee, or improper roasting, or when the final beverage is made. Positive odors are all those sensations that we can perceive, thanks to the good quality of the coffee beans and the ability of all the operators throughout the production chain. These are both distinct from richness, which can best be described as the multitude of positive sensations offered by a good espresso.
When dealing with this fundamental subject, we have used the word “aroma” to describe olfactive sensations and sensations perceived through the back of the throat. According to the ISO methodology, the word aroma only refers to the latter.
Positive and negative olfactive sensations, which are easily perceived when smelling an espresso, are defined in Italian semantic tables, and codified by the International Institute of Coffee Tasters.
The following list is certainly not an exhaustive one. Throughout the world many other lists have been compiled, according to the relevant country’s culture and tasting methodology. The appendix contains the list compiled by the International Coffee Organization (ICO).
As you will gather, the methodology proposed in this book is not prescriptive; it allows assessors to evaluate certain attributes not specifically codified. This flexibility of approach enables tasters to define some sensations that stem from cultural differences appropriately. It will also help people to register new attributes, which result from various processing techniques and coffee making methods.
Positive Odors
- Roasted
The dominant characteristic of coffee caused by particular components being formed as a result of sugar being transformed during the roasting process. - Chocolate-like
This is the typical aroma of good cocoa, which verges on vanilla. It is one of the best and most desirable aromas. - Flowery
Reminiscent of fresh flowers even though the single fragrance is difficult to recognize. It is the typical aroma of good coffee. It is particularly evident in good washed coffee that has been enriched by the action of certain microorganisms active during the roasting process. - Fruity
Reminiscent of fresh fruit. It is typical of washed coffee that has been badly roasted. - Toasted Bread
Complex characteristic resulting from a particular molecule that starts during Maillard’s reaction – a phase of the roasting process.
Negative Odors
- Straw
Denotes poor quality beans. - Stinker (Rotten Flowers)
This is an English term used to identify a group of unpleasant smells that are typical of rotten flowers. It comes from the involuntary fermentation of decomposed berries. - Grassy
This reminds us of the smell of fresh grass and green twigs. It is caused by particular aldehydes. It is considered to be a positive characteristic if it falls within certain parameters. - Smoky
This is considered to be a negative characteristic. - Riato (Rio Flavour)
This is a negative characteristic, reminiscent of wine corks, and is caused by fenic acid due to the presence of very small particles of tricloanisole. - Rancid
This reminds us of the smell of ham that has been sliced and left for a time. It is caused by fat oxidation. It is particularly evident in old coffee, coffee that hasn’t been packed properly, or coffee that has been left in the grinder for a long time. - Stagnant Water
This is caused either by dirty filters or by dirty filter holders. - Peanut
This is usually considered to be a negative characteristic, and is due to the presence of diacetyl – a specific ketone. - Wet Jute
This scent is absorbed by green beans that have been stored in wet jute sacks.
Taste
Taste is one of the poorer sense organs. We are able to perceive two sets of sensations when sipping coffee: true taste sensations and tactile sensations. There are only four tastes in the first group: sweet, bitter, acidic and salty. Tactile sensations are heat-related, astringency and physical consistency.
Papillae (taste buds) on the tongue are small organs able to recognize tastes. The taste buds on the tip of our tongues recognize sweetness, the ones on the side of the tongue, saltiness, and the ones on the border, acidity. Bitterness is recognized by the papillae on the bottom of the tongue.
Tactile sensations are very important as they help to determine a coffee’s profile. The temperature of the liquid gives the heat-related effects in espresso. Even though the habit of drinking cold coffee is spreading rapidly, espresso must be drunk hot, but not too hot. At 65 degrees centigrade we feel pain, and pain seriously compromises taste. Astringency is caused by the precipitation of a saliva protein and by specific poliphenols, which are present in high quantities in certain types of coffee. These poliphenols can attach themselves to the proteins of our oral membrane.
As a consequence, we feel a sense of dryness and sometimes our mouth sets (as if we were eating an unripe persimmon). Viscosity gives us an almost opposite sensation. This depends on the presence of microscopic solid particles and colloids- molecules of high molecular weight – which give sensations of roundness and thickness.
If such sensations are too strong they give us an unpleasant feeling of greasiness. In coffee, the presence of sugars, proteins, fats and colloids produce mellowness, while tannic substances give astringency. When mellowness is accompanied by a well balanced acidity, we experience a coffee with a good body and an excellent composition. This is very important as the substances that give coffee its composition and body are also good fixing agents of the scent molecules, which are slowly released, and prolong the pleasure of drinking it.
Gustative Sensation
- Sweetness
This is caused by residue sugars in roasted coffee. Over-roasting the beans diminishes sweetness and decreases the amount of glucides that, in green coffee, range from about 10% to a mere 2%, which is considered the optimum percentage. - Acidity
Acidity is caused by organic acids that measure about 7% before roasting and 4-5% afterwards. Coffee becomes less acid the more it is roasted. - Bitterness
This is usually felt on the bottom of the tongue. It is present in coffee and is considered a positive characteristic if it stays within certain parameters. It comes from sugar compounds during the roasting process, from burnt wood compounds, and from caffeine. It is more evident in Robusta.
Tactile Sensation
- Earthy and Woody
This sensation is caused by the diminished ability of saliva to lubricate. It is usually associated with tannin – a strongly bitter taste. Sometimes small particles, which taste of dirt, can emphasise these characteristics. - Astringency
This sensation is caused by the reduced ability of saliva to lubricate. Substances of tannic origin (poliphenolic acids) are responsible for the degradation of a saliva protein that allows lubrication. - Smoothness
This is directly in proportion with the quantity of microscopic solid substances and it increases with the increase of sweetness and fats. It decreases in the presence of bitterness and acidity. Smoothness is usually to be found in a rich, creamy espresso. It should be full, rich, vivid and fragrant, and the various tastes should be progressively distinguishable to offer tasters a succession of sensations.
**The information, which is reported in this section, is taken from the “ESPRESSO ITALIANO TASTING” book (published by Centro Studi e Formazione Assaggiatori).
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