The Coffee Science Foundation Announces New Cold Brew Extraction Research: Sensory Analysis of Full Immersion Coffee

A new publication has been released; entitled, “Sensory Analysis of Full Immersion Coffee: Cold Brew Is More Floral, and Less Bitter, Sour, and Rubbery Than Hot Brew,” the article was published in the journal, Food.

The Coffee Science Foundation alongside the Specialty Coffee Association is excited to announce this output from the Cold Brew Extraction research project. This project is underwritten by Toddy, LLC and the research related to this publication was performed by a research team led by DR. MACKENZIE BATALI, at the University of California, Davis.

This study found four sensory attributes which exhibited statistically significant variations in relation to brew temperature (variation were true for all origins and roast levels tested). Of the four, three attributes – bitter taste, sour taste, and rubber flavor – were all higher in hot brewed coffees, and one attribute – floral flavor – was higher in cold brewed coffee. However, it should be noted that there were several additional sensory attributes significantly impacted by temperature for specific origins and roast levels.

The methodology used was a 3 x 3 x 3 factorial design, with coffee from three different origins (El Salvador Cerro Las Ranas Honey varietals Bourbon, Pacamara, Sarchimor, Pacas, Catuai, and Caturra, an Ethiopia Guji Washed organic of indigenous heirloom varietals, and a Sumatra Fair-Trade Organic Takengon varietals Catimor, Tim Tim, and Abyssinia) representing different post-harvest methods (washed, honey-processed, and wet-hulled), each roasted to three different levels (light, medium, and dark), and each brewed at three different temperatures (4 °C, 22 °C, and 92 °C).

Figure 1. A schematic of the coffee brewing process and packaging for a remote COVID-19 descriptive analysis.

To maintain consistent sensory qualities across the test coffees, post-roasting treatment (roasted coffees allowed to degas for one week), storage (vacuum-sealed bags placed in a freezer maintained at -20 °C ) and brewing methods (brewed using Toddy Cupping Kits with Toddy paper filters) were kept consistent. Additionally, all coffees were brewed to equilibrium, then diluted to precisely 2% total dissolved solids (TDS) and served at the same cold temperature (4 °C)

Figure 4. Sensory attributes with significant differences by temperature across all roasts and origins with LSD letter codes indicating significant difference.

In addition to the four sensory attributes (bitter taste, sour taste, rubber flavor, and floral flavor) that varied consistently by brew temperature, each origin showed unique sensory differences due to temperature. The Ethiopia coffee across all roast levels showed a significantly higher burnt flavor in the 92 °C coffee than the 22 °C coffee or the 4 °C coffee. Conversely, fruity flavor was significantly higher in the 4 °C coffee than the 22 °C or the 92 °C coffee. The El Salvador coffee only had one additional attribute, woody flavor, that was significant across all roasts, which followed a slightly different trend: the 4 °C coffee had the highest woody intensity, the 22 °C coffee was significantly lower, and the 92 °C coffee was intermediate. The Sumatra coffee also had one significant attribute across all roasts, smoky flavor, which also followed a pattern similar but reversed to the El Salvador’s woody flavor. In the Sumatra coffee, the 92 °C coffee had the highest smoky flavor, with the 22 °C coffee significantly lower and the 4 °C coffee in the middle.

Overall, an analysis of the data revealed roast was the largest driver of difference among the coffees, with 20 attributes showing a significant difference by roast level. In general, the lighter roasts were more floral, fruity, and sour, whereas the darker roasts were more burnt, bitter, and roasted. Origin was the second largest driver of difference of the three experimental factors, with the analysis revealing 13 attributes that were significantly different by origin. The honey-processed El Salvador and washed Ethiopia coffees, for example, were generally more sour and fruitier than the wet-hulled Sumatra coffees, which were more vegetative and nuttier. Many of the differences by origin, however, were also dependent on the roast and brew temperature.

In conclusion, the research resulted showed that, at a fixed TDS and consumption temperature, brew temperature across the cold to hot range had a significant impact on the sensory attributes of coffee. The results presented also substantiate the general belief that cold brew is less sour, per descriptive analysis, but not necessarily less acidic chemically.

Synopsis by MARY BASCO, SCA Research and Knowledge Development Programs Manager.

“Sensory Analysis of Full Immersion Coffee: Cold Brew Is More Floral, and Less Bitter, Sour, and Rubbery Than Hot Brew,” an open-access article published in Food, was authored by Batali, M. E., Lim, L. X., Liang, J., Yeager, S. E., Thompson, A. N., Han, J., Ristenpart, W. D., & Guinard, J.-X.t. 

This project was made possible thanks to generous underwriting from Toddy, LLC.

Batali, M. E., Lim, L. X., Liang, J., Yeager, S. E., Thompson, A. N., Han, J., Ristenpart, W. D., & Guinard, J.-X. (2022). Sensory analysis of Full Immersion Coffee: Cold Brew is more floral, and less bitter, sour, and rubbery than hot brew. Foods, 11(16), 2440.

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