A recent study by a team from the University of California, Davis, suggests that the traditional full – immersion “cold” brewing method may not require as much time as is typically thought to achieve optimal sensory results.
Published in August last year in the journal Scientific Reports, this research offers fresh insights into how the final “cold” brews – whether they are brewed cold, at room temperature, or hot and then cooled – are influenced by factors such as brew time, brew temperature, and the roast level of the coffee.
For instance, the study indicates that shorter extraction times in cold or room – temperature brews, like eight hours instead of the commonly used 24 hours, could potentially offer similar flavors and other sensory qualities. This finding could make the production process more efficient for commercial coffee brewers.
The study, led by graduate researcher Jiexin (Jessie) Liang, states, “Our analyses consistently determined that, compared to roast level and temperature, brew time was the least significant factor in causing sensory differences among the full – immersion brewed coffee samples.”
In fact, the roast level of the brewed coffee emerged as the most significant determinant of sensory differences.
For the study, the research team utilized Salvadoran and Nicaraguan arabica coffees. These were roasted on a Probat drum roaster at the UC Davis Coffee Center, under the supervision of coffee roasting expert Juliet Han. From these, they created a “light” roast blend and a “medium – dark” roast blend, with Agtron readings of 41.8 and 71.8 respectively.
Subsequently, the blends were brewed at three different temperatures (4 °C, 22 °C, and 92 °C) for five different time intervals. This ranged from what could be considered a quickly – chilled hot brew to an extended cold brew where the total dissolved solids (TDS) reached equilibrium.
Thirty samples were analyzed for TDS, titratable acidity, and pH. Meanwhile, a calibrated panel of 14 coffee tasters used descriptive analysis to evaluate the sensory properties. The coffees were served cold to the panelists (around 6°C, warming up to approximately 12°C during the tasting period).
The article notes, “By combining these factors, a diverse range of flavor profiles were obtained from a single green coffee blend. Roast level was the primary driver of flavor, followed by temperature, and then longer brew times as TDS plateaued.”
However, different combinations led to diverse and sometimes unexpected outcomes. For example, the impact of time was more noticeable at lower brewing temperatures, but it also depended on the roast level for specific sensory attributes.
The study states, “For dark roasts, the changes in bitter and burnt attributes over time were significant in fridge – and room – temperature brews, while those in hot brews remained relatively stable. Conversely, for light roasts, sour and citrus attributes showed more pronounced differences in lower – temperature brews.”
In essence, there is no single definitive method for brewing cold coffee. It is important to mention that this research, which is part of a larger cold – brew research project supported by the non – profit Coffee Science Foundation, was funded by cold – brewing systems manufacturer Toddy LLC. The authors reported no competing interests.
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