Danish researchers bust myths about coffee and acid
In the coffee industry, there is a widespread narrative that you can taste the individual types of acids in coffee and even determine the country of origin based on the acid profile. However, a study from the Faculty of Engineering at the University of Southern Denmark concludes that this is not possible.
In brewed coffee, there are various types of acids, and especially in the specialty coffee industry, there is a widespread belief that they have a decisive impact on the coffee's flavor.
To be called a certified coffee taster, known as a Q Grader – somewhat similar to a sommelier in the wine world – one must pass a test in which they must taste and identify the four most dominant acids in coffee: citric acid, malic acid, phosphoric acid, and acetic acid.
There's just one problem: You can't do that.
This is the conclusion of a study conducted by researchers at the University of Southern Denmark (SDU).
- We conducted chemical measurements of acid in coffee and compared them with sensory tests. What we found out was that it is not possible to taste the acids at the concentrations found in coffee, says Christina Rune, a PhD student in biotechnology and sensory analysis at the University of Southern Denmark.
- We also conducted a test with professional coffee experts to see if they could identify different types of acid. But they couldn't, even when we spiked the acids, that is, chemically adding extra of the specific types of acid, says the researcher.
While the presence of a certain amount of, for example, malic acid or acetic acid in a coffee can contribute to a more acidic taste overall, she explains, individually the acids have no significance for the taste because the concentration is too low to be detected purely sensorily.
Myth busted
The study at the University of Southern Denmark also busts some of the myths about acid content in coffee and country of origin. For example, there is a notion that Kenyan coffee contains more acid than Brazilian coffee, but that does not seem to be the case.
- According to our measurements, Brazilian and Bolivian coffee actually generally contain more acid than Kenyan coffee, says Christina Rune.
This does not mean that Kenyan coffee cannot end up tasting more acidic, she emphasizes, but it could be due to many other factors, especially the roasting level, which apparently is more significant for the acid level than origin.
- The difference in taste between, for example, Brazilian and Kenyan coffee can also be due to them being roasted differently, brewed differently, or processed differently after harvest. All these factors influence the acid content.
Additionally, the PhD student has a hypothesis that the aromas in the coffee also play an important role:
- It is not something we have investigated yet, but I have a hypothesis that when a coffee tastes acidic, it could be related to its aroma profile. If a coffee is associated with fruit and berries, as Kenyan coffee often is, it could be perceived as acidic, not because it is chemically acidic, but because the aromas are associated with an acidic taste.
About the study
The study 'Acids in brewed coffees: Chemical composition and sensory threshold' is published in Current Research in Food Science in the spring of 2023 and written by Christina J. Birke Rune, Davide Giacalone, Ida Steen, Lars Duelund, Morten Münchow, and Mathias Porsmose Clausen.
In the study, the researchers examine the chemical composition of acids in specialty coffee, the threshold for when the acids can be tasted in coffee, and whether it is possible to identify the individual types of acid during a tasting.
The conclusion is that it is not possible to determine the different types of acid, and that the concentration of the different types of acid in coffee is too low for them to individually affect the taste of acid. Together, however, they can make the coffee more or less acidic. The researchers also found that the roasting level significantly affects the acid content, and that the country of origin has less significance for the acid content.
The study was conducted with two different sensory tests:
The first with 40 untrained participants, who were subjected to a so-called 2-AFC test. This means a test where they continuously received two different samples of coffee, which they had to taste and then assess which one was more acidic. One sample contained extra added acid of different types (citric acid, malic acid, acetic acid, lactic acid, or phosphoric acid) and in different concentrations, and the other sample did not contain extra acid.
Only the samples with citric acid were systematically identified as more acidic by the participants.
The second test examined whether coffee experts who work professionally with coffee could taste and identify the individual types of acid in coffee. There were 13 participants who, before the test, had 30 minutes to train by tasting citric acid, malic acid, acetic acid, lactic acid, and phosphoric acid in concentrated form. They were then served coffee and water with added acid - double the amount found in coffee - in a random order and asked to identify the types of acid. They couldn't.