Since the 10th century, coffee connoisseurs have sought after and crafted the best brews. This summer, senior chemistry major Sigrid Kiledal looked at the “perfect” cup of coffee through the lens of science.
Kiledal’s research project combined two of her interests: chemistry and coffee. She originally learned about the coffee-making process from her father, who roasts his own coffee.
“It’s always been something I’ve been interested in because my dad has been roasting coffee for a long time, just for fun,” she said.
For this project, Kiledal set out to analyze the amounts of caffeine and chlorogenic acid present in an ideal brew. Chlorogenic acids contribute to coffee’s acidity, which can corrode teeth and cause indigestion. Based on the data she collected, Kiledal would be able to find which coffee roasts had minimal acidity and high caffeine content while still falling within optimal brewing standards.
“Being able to look at what the instrument tells you and see how much is there, that’s really interesting,” Kiledal said. “A lot of coffees will say, ‘If you make it like this, you’ll have this much caffeine,’ but you don’t really know if that’s accurate or not.”
Kiledal is continuing to look at her data in-depth, but the trends show Kenyan coffee beans to be most acidic, with dark roasts generally containing more caffeine and less chlorogenic acid than light and medium roasts.
“It really looks like a darker roast actually yields more caffeine,” Kiledal said. “You would think that the caffeine would break down during the roasting process, but that does not seem to be the case.”
For her project, Kiledal followed international standards for the ideal cup of coffee, which differ from region to region.
“There’s something called a brewing ratio for what the ideal coffee is, and it depends on what country you’re in,” Professor of Chemistry Lee Baron said. “What you’re trying to do is get a coffee that fits in the ideal range.”
Organizations such as the Specialty Coffee Association of America, Specialty Coffee Association of Europe, and the Norwegian Coffee Association all offer standards for roasting and brewing coffee beans for an optimal cup of coffee.
Using these standards, Kiledal focused her research on coffee beans from Guatemala, Kenya, Maui, and Papua New Guinea.
But brewing the coffee was hardly the beginning. Before she could determine the levels of chlorogenic acid and caffeine, she first had to roast the green coffee beans, and then grind as well as brew the coffee in a consistent manner so the subsequent analysis would yield meaningful results. In the process, she had to develop a new method to analyze both components simultaneously.
“She was trying to look at a very complicated thing,” Baron said. “Coffee is hugely complicated, and that’s the issue. There are so many components, and you have to figure out a way to pick out just the ones you want to look at.”
Kiledal used a liquid chromatography instrument to separate the components of the coffee samples, and a mass spectrometer, which sorts out and measures the components according to molecular weight, to determine the levels of caffeine and chlorogenic acid present in each coffee brew.
“After it goes through the chromatography column, then those individual portions go into the mass spectrometer,” Professor of Chemistry Mark Nussbaum said. “Then you’re looking specifically for a given mass. The mass spectrometer gives you the ability to detect and quantify what’s there at one particular mass, but it also allows you to scan a range of masses so you can get a full mass spectrum.”
She then compared the readings from the coffee samples to standards of pure caffeine and chlorogenic acid prepared at known concentrations.
“That’s what they do in crime labs, that’s what they do in hospital labs,” Baron said. “They only know how much of something is in a sample if they have standards [to compare it to].”
Baron said Kiledal’s detailed preparation of the coffee and the extra work she put into ensuring her results were reproducible made her project stand out.
“People have looked at coffee and caffeine for forever, but the way she went about it and chose her variables was unique,” Baron said.