Yuba-Sutter's 'coffee nerd' joins UC Davis researchers in roast study

Michaela Harris, Appeal-Democrat, Marysville, Calif.
Updated ·4 min read

Apr. 17—To those who can't function without a morning cup of coffee, the relationship between roast profile and acidity may be common knowledge. However, researchers at the University of California, Davis Coffee Center sought out the "why."

With the help of CEO and head roaster at Bridge Coffee Co. Tim Styczynski, researchers were able to assess the effects of roast profiles on titratable acidity in coffee during the roasting process.

According to the UC Davis School of Viticulture and Enology, titratable acidity measures the total acid concentration found in food or beverages. It differs from pH balance, which measures the strength of an acid.

Published on April 8 by Scientific Reports, the study was conducted by the UC Davis Coffee Center under the College of Engineering and states that titratable acid has long been correlated to the perceived sourness in brewed coffee. Acidity can be influenced by the coffee's origin, processing method and brewing conditions, but roast profile is considered one of the more crucial factors due to its effect on the coffee's flavor and aroma.

"It is a lot like how a winemaker approaches the grapes they have. You have a hundred winemakers with the same grapes, and you end up with 100 different-tasting wines. The same thing happens with coffee. Our research is answering the question of why and how," Styczynski said.

The Coffee Center is dedicated to conducting academic research entirely centered on coffee and its scientific and cultural components. As someone who proudly wears the title of "coffee nerd," Styczynski has been following the center's work since its inception in 2013 and reached out to offer his assistance wherever appropriate.

"I reached out to the director and I just said, 'I'm in your backyard. I own a coffee roasting and retail business. I love what you do and I've been obsessive about coffee for 30 years. Is there anything that I could do to lend a hand that would be valuable?' And it turns out there was," he said.

For this study, Styczynski was able to provide seven different roast profiles varying in initial heat application and time of roasting: fast start, slow start, medium, production, exaggerated flick, negative rise and extended Maillard. Each sample was roasted in a five kilogram batch roaster for 16 minutes.

Styczynski compares the roasting process to making popcorn given how coffee beans crack open under heat. For the purpose of this experiment, the beans were roasted until they were "practically undrinkable" to see the entirety of chemical processes during roasting, Styczynski said.

After assessing each of the seven profiles, researchers observed a "significant increase in (titratable acidity) from the beginning of the roast until the first to second crack phase where the (titratable acidity) peaked." Then, it significantly decreased until the end of the roast. These findings are consistent with previous studies, the study said.

However, this study provides two new observations: peak titratable acidity always occurred concurrently during the first crack, and the acidity decreased to its initial value with the onset of the second crack.

Researchers suggested that the increase in titratable acidity is due to the formation of formic and acetic acids from carbohydrates while the decrease results from the degradation of organic acids.

"Our results suggest that by applying specific and different roast profiles, roasters can control the (titratable acidity) of coffee during roasting, and thus regulate its perceived acidity or sourness," the study said.

In a typical brew, roast profiles offer different flavor characteristics and bodies for the beverage, resulting in varying notes and textures.

"The combination of all those sensory attributes leaves a lot of flexibility in the roaster's hands to help highlight the quality of the coffee or at least create a style of coffee. Those are two very different things," Styczynski said.

The study was conducted between July and December 2022, which created its own challenges in ensuring consistency when collecting samples, Styczynski said.

"We went through two and a half seasons of changing weather and the roasting process is affected if it's raining or super humid outside. Being able to recreate those profiles exactly was a difficult, but fun challenge," he said. "I have 25,000 roasts under my belt, roasting for nearly 30 years, and I'm still always learning. To be surrounded by such wonderful, intelligent people, to be a part of it: I have grown and I'm so excited to share this with my peers, the industry and even let consumers know what they're enjoying."