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Wednesday, April 24, 2024

UC Davis Coffee Center review lays the foundation for future coffee investigations

A recent meta-analysis on acid concentrations in coffee consolidates existing data, revealing both trends, gaps in the literature


By VICTORIA MCJUNKIN –– science@theaggie.org


The distinct aroma and flavor of a cup of coffee are largely determined by its chemical composition, specifically its acid concentration. However, the literature on acids in coffee—while abundant—remains disjointed and scattered. A recent review published by the UC Davis Coffee Center centralizes the data from preexisting research, allowing for a close evaluation of varying acid concentrations across coffee roasts and their effect on the final sensory profile.

“This project is instrumental in many ways to cold brew and coffee and acid research just because it’s a compilation of everything that’s been done before,” Sara Yeager, lead researcher and coffee scientist at Toddy, said. “It serves as the springboard for many different experiments.”

The project began as standard background research for a study Yeager hoped to perform on cold brew coffee. But as she gathered information on acid concentrations in coffee, she noticed inconsistencies within the existing literature. What was intended to be only 10 to 12 pages of research turned into a review of 129 publications, with a compilation of nearly 8,000 data points.

“It just kept growing and growing,” Yeager said. “There hasn’t really been any cross literature comparison. While attempts at doing such a thing have been done before—in chapters and books—no one has really directly compared the data from the papers.”

Acid concentrations in coffee play an important role in a cup’s final sensory profile, but coffee researchers document acid levels inconsistently, according to the review.  Acids are linked to contrasting flavors, roast levels (light, medium or dark) are loosely defined and the same acids are associated with both negative and positive consumer ratings across different works.

“I would say coffee researchers like to march to the beat of their own drum: they all do things their own specific way,” Yeager said. “So it makes it really hard to do cross-comparison, because there’s not really a standardized way to define roast level, or how the acids are extracted and analyzed, or how they’re brewed. The goal of this research became to find a way to comprehensively look at all of the literature that’s out there—a one stop shop for all the data that will help future researchers decide where they want to go.”

Yeager said she took on the task of standardizing the data before analysis, creating a series of graphs that plotted an acid’s concentration levels in coffee at different roasting levels: green, light, medium and dark. Yeager’s work evaluated both organic and chlorogenic acids across arabica and robusta coffees, producing not only the easy-to-reference figures, but also a massive database of the raw data.

The database, combined with the figures, serves as a comprehensive resource for future coffee research and allows for a thorough analysis of trends in coffee acid concentrations.

“We tried to standardize things as much as possible, and that was a really big feat in and of itself,” Yeager said. “The ultimate achievement [is] those graphs that are in the publication: something that any person can take a glance at and know, almost instantly, how the acids will differ based on coffee or based on roast level.”

Yeager stated that the review also enabled her to identify trends and gaps in the existing literature. According to the paper, research centers around medium roast coffee, with less attention paid to light and dark roasts. Researchers also tend to focus on robusta and arabica coffee instead of smaller, niche species, and focus primarily on five core acids out of 37 organic acids.

In addition to evaluating acid concentration levels in coffee, the review also explored how each acid affects the final sensory profile.

“To date, there has not been any direct comparisons of sensory profiles to acid levels. It’s all been very one or the other,” Yeager said. “For example, while organic acids contribute sourness—especially acetic acid, which contributes vinegary tastes—they interact in very complex ways where it’s not a one-to-one translation. The acids themselves add a sour note, but they’re also flavor enhancers. So you might get more floral, you might get more fruity, you might get more nutty-type notes.”

Mackenzie Batali, a postdoctoral scholar at the UC Davis Coffee Center, wrote the paper’s sensory analysis, drawing upon her work on acids in cold brew coffee and matching mass spectrometry readings of coffee to sensory science.

“I think it’s important to note, especially for the coffee industry, that acidity is not synonymous with sourness,” Batali shared. “Some of the acids that are really high-concentration in coffee like quinic acid, for example, aren’t sour at all. You can get a really high-measured acidity of a cup of coffee and not have it be particularly sour because quinic acid is very bitter.”

While a meta-analysis of acid data will assist in future coffee research, the implications of Yeager’s work resonate beyond the academic sphere. Raymond Rimas, Coffee Quality Specialist at Philz Coffee, appreciates science’s ability to enhance existing knowledge, and echoed the idea that an interaction of acids creates a nuanced sensory profile.

“In terms of acids, we do look for specific characteristics and acids and our particular copies that we source,” Rimes said. “If you understand more about the acids, you might understand a link between one thing and another that you didn’t realize was there. Having a vast library of organic acids is great.”

When searching for notes of cranberries or green apple, Rimas said he looks for malic acid, and when vanilla flavors mix with certain acids, it sometimes gets classified as melon or nectarine. Although Philz has been able to create wonderful products relying on human tasters, Rimas explained that having the technical, scientific knowledge helps in flavor identification and in formalizing his expertise into a more solid framework.

“People in the coffee world don’t always come with a background of skills and knowledge—they acquire them,” Rimas says. “We’re always trying to adapt and learn more to better our position. So we’re always open to research, especially from World Coffee Research, or the SCA, or UC Davis—we grasp everything we can, and we try to make decisions based on what we have in front of us.”

Written by: Victoria McJunkin — science@theaggie.org


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