If you ask people to describe the taste of black coffee, most often they will answer: "Bitter". But people, even with a little tasting experience, recognize in this drink acidity, sweetness and various descriptors - floral, fruity and others.
We have already discussed how adding sugar affects the taste of coffee . But today we will talk about something else - about the natural sweetness of black coffee, which is not so easy to achieve. And it does not depend on the sugar content.
The sweetness of the drink can change from the harvest of the grains, from minor changes in roasting and preparation - science has not yet revealed an unambiguous relationship. The aim was to find out what and how influences the natural sweetness of the drink.
How was the study
Scientists decided to analyze how the chemical and sensory characteristics of coffee change during the brewing process. For this, fractionation was carried out - the drink was divided into fractions (portions) during preparation. This made it possible to evaluate the taste of the coffee at different stages.
The experiment used coffee from the Huila region of Colombia (54 on the Agtron scale ). It was cooked at 91.5 ° C for 4 minutes in a drip coffee maker. During this time, the container was changed every 30 seconds. The first fraction was taken in the range from 0 to 30 seconds, the second - from 31 to 60 seconds, and so on. As a result, we got 8 different factions. Then another coffee of the same kind was prepared, but not divided into fractions.
An expert panel was consulted to evaluate the taste of the resulting samples. Its participants worked differently from the experts : the task was to assess not the quality of the drink, but only the intensity of its sensory characteristics.
To get into the group, the experts underwent a triangulation test: they determined which of the three coffee samples was different from the other two. After the selection, the group went through a calibration procedure for several weeks using the SCA flavor wheel .
During the experiment, the participants sampled coffee samples in special isolated booths with red lighting so as not to base the assessment on the color of the brewed coffee.
The experts were faced with the task of objectively evaluating 9 samples (8 fractions and one whole) by 23 taste and aromatic characteristics - bitter, sour, floral, berry, and so on. All drinks were served blindly in random order, 3 times each. Each fraction was pre-measured by physical parameters, including the TDS. This figure reflects the actual strength of the drink.
In total, the expert panel rated 324 servings of coffee.
How the taste of coffee changed
On average, experts rated the first fraction as the most bitter. The bitterness intensity gradually decreased from the first to the last fraction.
The decrease in perceived bitterness correlated with the TDS of each faction: the early fractions had a high TDS, while the later ones dropped almost tenfold. It turns out that the more bitter the drink, the higher the concentration of dissolved molecules in it: the late fractions turned out to be less bitter in taste, because they were less concentrated. Some sensory characteristics (acidity, astringency and smokiness) also decreased with decreasing strength.
But the sweetness in later fractions, on the contrary, increased. There has also been an increase in the intensity of other flower, honey and fruit descriptors valuable to the specialty industry.
This result is surprising in that the later fractions have a much lower TDS. It turns out that the fewer coffee molecules in a liquid, the sweeter it is. This is paradoxical for sensory science, because if you add more sugar to the water, it will become sweeter, and not vice versa.
The lower the strength, the sweeter the coffee - why?
Several theories have arisen on this subject.
The first theory is that the later fractions have a higher concentration of dissolved natural sugars.
About 10% of the mass of green Arabica beans is sucrose. It usually does not withstand the roasting process, as it is involved in many complex chemical reactions. During frying, complex carbohydrates are broken down into monosaccharides - simple sugars. They also provide a tangible sweetness. So one possible explanation is that monosaccharides (fructose or glucose) are more slowly extracted from coffee during preparation. Accordingly, they give higher concentrations in the late fractions, which means more sweetness.
To test this theory, the scientists measured the concentration of monosaccharides in each fraction using liquid chromatography and mass spectrometry. The first fraction showed the highest concentration of sugars, which consistently decreased in later samples.
Surprising fact: the total concentration of all sugars in any fraction turned out to be significantly lower than the threshold of human sensory perception of sugars. This means that the experts could not sense the sweetness from the sugar in the samples tested. It turns out that sugar is not responsible for increasing the sweetness in later samples, but something else.
The second theory is that the human brain defines some taste qualities as sweet. This hypothesis is consistent with the observation that sweetness increases with the appearance of flower, honey, and fruit descriptors.
The third theory is that the higher concentration of bitter and sour compounds in the early fractions suppresses or "masks" the sweetness. Therefore, it is more pronounced only in later fractions, where there are fewer bitter and acidic compounds.
More research is needed to refute or prove the second and third theories. While experts are more inclined towards the third.
Food for thought and experimentation
The study found that the natural sweetness of coffee does not depend on sugars. It appears brighter towards the end of the preparation of the drink. Most likely, this is due to the fact that in the later fractions there are less bitter and sour compounds that mask the sweetness in the initial stages.
These results open up a new avenue for baristas to be creative: one drink can have several different flavor characteristics. You can choose which fractions to combine to get a different result for the client's request. For example, coffee made from bitter and sour early fractions may appeal to those who prefer adding cream and sugar. And the drink from the sweeter late fractions will be appreciated by those who like coffee without additives with light tea, floral, fruity and sweet notes.