HS-SPME/GC-MS Tracks How Ultrasound Boosts Coffee Flavor

Researchers wanted to find out how using ultrasound waves before fermentation affects coffee beans, both raw, green beans and beans that have gone through fermentation, looking at everything from their physical structure to the beneficial compounds inside them and how they ultimately taste and smell. Employing headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) revealed that the fermented beans had fewer of the aroma compounds linked to burnt, nutty, or medicinal smells, and more of the compounds tied to sweeter, fruitier, and more pleasant notes. Using this technique helped them trace how ultrasound treatment combined with fermentation might be triggering chemical changes that shape flavor. The findings offer fresh insight into using ultrasound as a pretreatment step for fermenting Robusta coffee, suggesting it could be a promising way to boost coffee quality. A paper based on this research was published in the journal Ultrasonics Sonochemistry.¹

Why Is Improving the Flavor Quality of Robusta Coffee an Important Research Goal?

Coffee is one of the most popular drinks in the world, loved for its rich, complex flavor and aroma. When it comes to the coffee beans that actually make it into your cup, two varieties dominate the market: Arabica, which makes up around 70% of global production, and Robusta, which accounts for roughly the remaining 30%,²As Robusta is widely used in instant coffee and espresso blends,³ improving its sensory quality and resulting added value, according to the authors of the paper,¹ “has become an important research objective for both academia and industry.”

How Does Ultrasound Treatment Work, and What Is Already Known About its Use in Coffee Processing?

Ultrasound has become a popular eco-friendly processing method that does not rely on heat to work. Instead, it uses sound waves to create tiny bubbles that rapidly form and collapse, a process that generates powerful shear forces, tiny jets of energy, and brief bursts of intense heat and pressure on a microscopic scale. That energy is enough to break open plant cell walls and make plant tissue more porous, allowing things to pass through it more easily.⁴ When it comes to processing coffee, studies have shown that treating beans with ultrasound alongside a soak in organic acids can improve the flavor of Robusta coffee, while also cutting down on certain compounds linked to less desirable, harsher off-flavors.⁵

“However,’ write the paper’s authors,¹ “its use as a pretreatment to enhance yeast fermentation in coffee beans has received limited attention. In particular, the combined effects of ultrasound and microbial fermentation on precursor transformation and flavor development in coffee remain unclear.”

Can Combining Ultrasound Treatment with Fermentation Improve the Flavor and Quality of Robusta Coffee?

The researchers report that their study looked at combining ultrasound treatment with a two-microbe fermentation process (using two specific strains of yeast, P. fermentans and K. marxianus) to see if it could improve Robusta coffee, both in terms of the beans' physical structure and their eventual flavor. The team tested three different ultrasound intensities and found that a medium level worked best, giving the yeast the biggest boost during fermentation. Compared to untreated beans, the combined ultrasound-and-fermentation approach boosted beneficial plant compounds like flavonoids and polyphenols, while also lowering caffeine and chlorogenic acid, a compound linked to bitterness, levels.¹

When it came to actual taste testing, the beans treated with the medium-intensity ultrasound scored the highest, with tasters picking up notes of roasted flavor, cocoa, florals, and honey. Digging deeper into the chemistry, the team found that this treatment cut down on some less desirable aroma compounds (ones that can smell overly nutty, burnt, or medicinal) while boosting the compounds responsible for fruitier, sweeter, and more pleasant notes.¹

Broader chemical analysis showed that ultrasound treatment triggered noticeable shifts in the beans' internal chemistry, changes that continued to evolve during fermentation and were tied to key pathways involved in building up the flavor compounds that ultimately shape how the coffee tastes.¹

“These findings,” write the authors of the paper,¹ “provide a potential strategy for improving the sensory quality and value-added utilization of Robusta coffee.”

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References

1. Ni, J.; Tang, H.; Tang, H. et al. Synergistic Effects of Ultrasound and Yeast Co-fermentation on Microstructural, Metabolic, and Sensory Properties of Robusta Coffee. Ultrason Sonochem. 2026, 133, 108030. DOI: 10.1016/j.ultsonch.2026.108030
2. Hu, F.; Yu, H.; Fu, X. et al. Characterization of Volatile Compounds and Microbial Diversity of Arabica Coffee in Honey Processing Method Based on Different Mucilage Retention Treatments. Food Chem. X2025, 25, 102251. DOI: 10.1016/j.fochx.2025.102251
3. Dias, R. C. E.; Valderrama, P.; Março, P. H. et al. Quantitative Assessment of Specific Defects in Roasted Ground Coffee via Infrared-Photoacoustic Spectroscopy. Food Chem.2018, 255, DOI: 132-138. DOI: 10.1016/j.foodchem.2018.02.076
4. Singla, M.; Sit, N. Application of Ultrasound in Combination with Other Technologies in Food Processing: A Review. Ultrason. Sonochem. 2021, 73, 105506. DOI: 10.1016/j.ultsonch. 2021.105506
5. Lee, H.; Yim, J.; Lee, Y. et al. Effect of Organic Acid-soaking and Sonication on the Formation of Volatile Compounds and α-dicarbonyl Compounds in Robusta coffee. Ultrason. Sonochem.2023, 99, 106580. DOI: 10.1016/j.ultsonch.2023.106580