What are retronasal-aroma odorants, and why are they important in coffee manufacturing?

The retronasal-aroma (RA) odorants are volatile compounds that contribute to the aroma we perceive through the back of the nose while drinking coffee. They are crucial for the overall flavor experience. A study by Michio Ikeda and team identified 33 key odorants, which were then classified into 19 distinct odor-description groups. Manufacturing processes like heat sterilization and pH adjustments can significantly alter these delicate RA odorants, affecting the final aroma of the coffee.

How does pH adjustment affect the aroma of coffee, and what is its impact on RA odorants?

Adjusting the pH of coffee extract can significantly diminish the total odor intensity, reducing the charm value (CMV) of coffee RA odorants by approximately 68%. This means that controlling pH levels during coffee manufacturing is essential for preserving the desired aroma. High pH results in less volatile compounds.

What is blending-after-sterilization (BAS), and how does it help in preserving coffee aroma compared to traditional methods?

Blending-after-sterilization (BAS) is a novel process where coffee is blended with milk after the sterilization process. This technique helps retain a significantly higher proportion (83%) of the original coffee aroma compared to traditional blending-before-sterilization (BBS) methods (approximately 56%). BAS avoids pH adjustment of the coffee, which helps preserve volatile aroma compounds that would otherwise be lost.

What is infusion (INF) sterilization, and why is it better for preserving aroma when used with reconstituted milk (r-milk)?

Infusion (INF) sterilization is a method of sterilizing reconstituted milk (r-milk) that, when used within the BAS process, proves superior in preserving coffee aroma. Specifically, INF-sterilized r-milk retains 91% of the original aroma, compared to 83% when using plate (PLT)-sterilized r-milk. This is because INF sterilization is a gentler process that minimizes the degradation of volatile aroma compounds.

What does Principal Component Analysis (PCA) reveal about the impact of pH adjustment versus sterilization techniques on coffee aroma, and why is this significant?

Principal component analysis (PCA) highlighted that coffee pH adjustment has a more profound impact on odor characteristics than sterilization techniques. This underscores the critical importance of pH control in preserving the desired aroma profile of coffee. The BAS process using INF sterilization creates aroma characteristics remarkably similar to homemade coffee, where unsterilized coffee is blended with PLT-sterilized milk, thus offering a closer-to-home experience in RTD beverages.

Surreal illustration of coffee aroma molecules transforming during the manufacturing process.

Unlocking the Perfect Brew: How Manufacturing Affects Your Coffee's Aroma

Nico Varela in Science & Nature August 2025 • 4 min read.

"Discover how different processing conditions impact the retronasal-aroma odorants in your milk coffee, ensuring a richer, more authentic taste every time."

For many, a cup of coffee is more than just a morning ritual; it's an experience. The complex interplay of flavors and, crucially, aromas, sets the stage for the day. Ready-to-drink (RTD) milk coffees offer convenience, but often at the expense of that authentic, freshly brewed taste. The challenge? To capture and preserve the volatile compounds that make each sip memorable.

The key lies in understanding how manufacturing processes affect these delicate aroma compounds. Traditional methods, designed for stability and shelf life, can inadvertently strip away the very essence of what makes coffee so appealing. Heat sterilization and pH adjustments, while essential for safety and preservation, can alter the delicate balance of retronasal-aroma (RA) odorants – those scents we perceive through the back of our nose as we drink.

Now, researchers are diving deep into the science of coffee processing, seeking ways to minimize flavor loss and deliver that genuine coffee experience in every RTD beverage.

The Science of Scent: Unpacking Retronasal-Aroma Odorants

Surreal illustration of coffee aroma molecules transforming during the manufacturing process.

A groundbreaking study led by Michio Ikeda and team, published in the Journal of Food Science, investigated how different manufacturing conditions impact the retronasal-aroma (RA) odorants in milk coffee. Using gas chromatography-olfactometry (GC-O) coupled with an RA simulator (RAS), the researchers meticulously analyzed the volatile compounds released during various processing stages. They identified 33 key odorants, classifying them into 19 distinct odor-description groups, providing a detailed map of coffee's aromatic landscape.

The study revealed some striking effects of common manufacturing practices:

pH Adjustment Impact: Adjusting the pH of coffee extract significantly diminished the total odor intensity, reducing the charm value (CMV) of coffee RA odorants by approximately 68%.
Ultra-High-Temperature (UHT) Sterilization: UHT sterilization, while crucial for safety, had a subtler impact, increasing the total CMV by a modest 6% to 7%.
Blending-After-Sterilization (BAS) vs. Blending-Before-Sterilization (BBS): A novel blending-after-sterilization (BAS) process, which avoids pH adjustment of the coffee, retained a significantly higher proportion (83%) of the original coffee aroma compared to traditional blending-before-sterilization (BBS) methods (approximately 56%).
Infusion (INF) Sterilization Superiority: Within BAS processing, using infusion (INF)-sterilized reconstituted milk (r-milk) proved superior, preserving 91% of the original aroma compared to plate (PLT)-sterilized r-milk (83%).

Principal component analysis (PCA) further highlighted the importance of pH control, indicating that coffee pH adjustment had a more profound impact on odor characteristics than sterilization techniques. The BAS process using INF sterilization emerged as the frontrunner, producing a milk coffee with aroma characteristics remarkably similar to homemade versions where unsterilized coffee is blended with PLT-sterilized milk.

A New Dawn for RTD Coffee: Preserving the Perfect Aroma

The findings of this study pave the way for a new generation of RTD milk coffees that deliver on both convenience and authentic flavor. By understanding the delicate interplay of manufacturing processes and aroma preservation, producers can now leverage innovative techniques like BAS and INF sterilization to create beverages that truly capture the essence of freshly brewed coffee. For coffee lovers, this means a richer, more satisfying experience in every sip, no matter where they are.