Why Is an Espresso So Good? Food Chemists Unravel Hidden Dynamics of Milk in Coffee

Research indicates that adding milk to coffee does not alter the molecular structure of milk proteins, ensuring the consistency of taste and texture in coffee drinks.

The swirl of milk and espresso — a small storm in your mug — doesn’t impact the dynamics of the milk proteins, according to research published in ACS Food Science & Technology. Researchers conducted a detailed molecular analysis to explore how milk proteins and caffeine molecules behave in water and coffee. They discovered that the molecular structures of the milk proteins are preserved, ensuring that they maintain their natural texture and flavor in your daily coffee.

Pouring milk into coffee causes the proteins to interact (e.g., combine or repel) with compounds extracted from the roasted, ground coffee beans, and that could change the proteins’ mouthfeel and the way they are digested. Milk proteins could also potentially affect the absorption, or bioavailability, of caffeine by the human body. To shed light on these mysteries, Tobias Weidner and Fani Madzharova used 2D infrared spectroscopy to investigate milk proteins’ molecular structures and dynamics when in a coffee beverage. They assessed increasingly complex mixtures of a store-bought whole fat (3.5%) milk, water solutions with milk and caffeine, and then a handmade cappuccino.

They found that the folding of milk proteins was unaltered by the presence of caffeine in these beverages, even in the cappuccino, which contained components extracted from the coffee grounds, such as chlorogenic DOI: 10.1021/acsfoodscitech.4c00070

The authors acknowledge funding from the Novo Nordisk Foundation, the Danish National Research Foundation through the Center of Excellence for Chemistry of Clouds, and the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska−Curie Grant.