The Chemistry of Cold-Brew Coffee

Jefferson researchers examine the science behind the popular pick-me-up.

The world’s thirst for cold-brew coffee continues to grow, but despite its popularity, scientists know little about the drink’s chemical makeup. A new study by Jefferson researchers—including an undergraduate student—looks to fill some of the gaps.

Chemistry professors Drs. Niny Rao and Megan Fuller and pre-medical studies student Meghan Grim found health-promoting antioxidants in cold-brew coffee can differ significantly from traditional coffee prepared with the same beans, particularly for dark roasts.

Student Meghan Grim and chemistry professor Dr. Niny Rao work in the lab
Pre-medical studies student Meghan Grim (left) says working with Drs. Niny Rao (right) and Megan Fuller on the cold-brew coffee study fostered her love for chemistry.

Through this work, Grim had the rare opportunity to have research published as an undergrad. She says teaming up with Drs. Rao and Fuller fostered her love for chemistry, gave her scientific endeavors structure and direction, and strengthened her diagnostic and critical-thinking skills and appreciation of data.

“I learned theories behind instrumental analysis and discovered so much more about the characteristics of the chemical compounds composing coffee, which is such a cross-culturally important beverage,” Grim says. “I lived the scientific process firsthand, learning the ability to diagnose and solve problems in methodology to ensure good study design is just as vital as performing data analysis and interpreting results.”

Drs. Rao and Fuller met Grim in 2018 when she spent time as a lab student worker. The faculty members invited her to join their project last summer after she showed interest in their previous cold-brew coffee research.

“She has been a fantastic and valuable team member,” says Dr. Rao, noting their work together helps to build the scant knowledge base on the drink’s chemical features. “Because cold-brew is such a new trend, the research hasn’t caught on yet.”

In the cold-brew process, ground coffee is mixed with room-temperature or colder water and steeped for as long as two days, sometimes in a refrigerator. With hot brewing, ground coffee is mixed with boiling or near-boiling water and steeped for a few minutes at most. For both, the coffee grounds are sometimes pressed, and the beverage is then filtered to remove the grounds.

For the latest study, the team found similar amounts of antioxidants in hot- and cold-brews with the lighter roasts. With the dark roasts, however, hot-brewing extracts more antioxidants from the grind than cold-brew. The difference increased with the degree of roasting, Dr. Rao says. This means hot-brew of dark roasts produces a potentially healthier drink.

Popular Mechanics, Ars Technica, Food and Wine and numerous other news outlets wrote about their study released earlier this month.

Drs. Megan Fuller and Niny Rao in the lab
Drs. Megan Fuller and Niny Rao have published several studies on the chemistry of cold-brew coffee.

“To me, being able to publish this work adds an important source to a novel body of literature,” Grim says. “It allows consumers to make informed decisions supported by chemical research about how to craft coffee beverages.”

This summer, Grim will conduct research at the Brady Urological Institute at Johns Hopkins University and prep for the MCAT. She believes the time spent in the lab with Drs. Rao and Fuller will allow her to stand out as a medical school applicant and future healthcare provider.

With Grim moving on to the next step in her career, Drs. Rao and Fuller will invite other Jefferson undergrads interested in their research to join them on their next study. The team will compare the impact of the two brewing processes and degree of roast on furans, flavor compounds present in raw coffee beans also generated through roasting.

Dr. Rao anticipates the next study—likely out in spring 2021—also will resonate with coffee drinkers.

“Cold-brew is a very new phenomenon,” she says. “Judging by the response from our studies, a lot of coffee enthusiasts are curious about the science behind the brewing process.”

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Science and Technology