Essential Science: We shouldn’t like coffee, but we do

Posted Nov 26, 2018 by Tim Sandle
It may seem like a strange question and one that could be posed at any food or beverage. However, with coffee the bitter taste means that humans should not really like the drink. But we do, and science offers an answer.
A cup of coffee at a cafe.
A cup of coffee at a cafe.
With most animals a bitter taste signals danger, something to be worried about and warning not to taste any more. This is designed to protect the animal from harm in relation to ingesting a toxic substance. For this reason, scientists have long assumed that bitter taste evolved as a defense mechanism to detect potentially harmful toxins in plants.
To a degree, though, humans have evolved. Over time humans have adapted to specific environments that contain different types of food. This has tailored our sense of taste and our genome and individual genes.
Does this explain why we like the bitter taste of coffee? By evolutionary logic, we should, despite the potential adaptation, want to spit it out. Coffee is naturally bitter, although bitterness does vary according to the processing of coffee beans. Processing rests on extraction, which is the process that pulls the flavor out of the coffee, turning clear water into the dark brew. When water mixes with the coffee grounds, a chemical reaction happens that dissolves flavor compounds.
Coffee is a brewed drink prepared from roasted coffee beans, the seeds of berries from certain Coffea species, first brewed by the Oromo people in a region of Kaffa, Ethiopia. Today coffee is grown in over 70 countries.
New research from Northwestern Medicine, U.S., and QIMR Berghofer Medical Research Institute in Australia has found that the more sensitive people are to the bitter taste of caffeine, the more coffee they drink. It seems this sensitivity is caused by a genetic variant.
Speaking with Laboratory Manager magazine, Professor Marilyn Cornelis explains: “You'd expect that people who are particularly sensitive to the bitter taste of caffeine would drink less coffee. The opposite results of our study suggest coffee consumers acquire a taste or an ability to detect caffeine due to the learned positive reinforcement (i.e. stimulation) elicited by caffeine."
Coffee Beans
A pile of coffee beans
This means that those who have a heightened ability to taste coffee's bitterness, especially the bitter flavor of caffeine, come to associate "good things with it”.
This was drawn out by research which examined a cross section of the population. Scientific analysis also showed that those who were more sensitive to caffeine and were drinking a lot of coffee tended to consume low levels of tea. Hence, there appeared to be a difference between tea and coffee drinkers.
A coffee picker collects coffee in the mountains near Ciudad Bolivar  Antioquia department  Colombia...
A coffee picker collects coffee in the mountains near Ciudad Bolivar, Antioquia department, Colombia on October 18, 2017. October is the peak of the coffee harvest season in the region of Ciudad Bolivar, one of Colombia's most productive coffee towns, employing over 25,000 coffee pickers from all over the country between October and December
The experimental design tested out the causal relationship between bitter taste and beverage consumption. The section of people profiled ran to over in more than 400,000 men and women based in the U.K. With a smaller test population the genetic variants linked to caffeine, had earlier been assessed via genome-wide analysis based on solution taste-ratings. The genetic variants were tested for associations with self-reported consumption of coffee, tea, and alcohol in relation to the wider subject population.
Even though taste has long been studied by scientists, the biological basis still intrigues and there remains much to learn about the relationships between people and food.
It was also found that people who were sensitive to the bitter flavors of quinine tended to avoid coffee. People who dislike coffee also tend to drink less alcohol, especially red wine.
The research has been published in the journal Scientific Reports. The research paper is titled “Understanding the role of bitter taste perception in coffee, tea and alcohol consumption through Mendelian randomization.”
Essential Science
PET scans showing the differances between a normal older adult s brain and the brain of an older adu...
PET scans showing the differances between a normal older adult's brain and the brain of an older adult afflicted with Alzheimer's disease. — On photo (left to right): PET scan of normal brain, PET scan of Alzheimer’s disease brain.
National Institutes of Health
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we took in a study that showed how different sides of the brain do specialize and that hemispheric dominance does occur.
The week before we outlined a new sensor that can monitor oxygen levels inside the human body, by scanning the surface of the skin. The new device can be used to track the progress of oxygenation in relation to healing wounds in real time, providing valuable medical data.