Global coffee consumption is rapidly increasing, and cold-brew coffee has become increasingly popular due to its perceived health benefits, lower acidity, and less bitterness compared to hot-brewed coffee. However, traditional cold brewing is a time-consuming process, requiring several hours or even days. This limitation hinders both consumer convenience and product development. Current automation attempts have not significantly reduced extraction times. This research explores a novel approach using laser-induced processing of colloids (LSPC) to accelerate cold brewing. LSPC has been successfully applied to inorganic materials, but its application to organic materials like coffee is less explored. This study investigates the potential of using picosecond-pulsed laser extraction (ps-LPP) to achieve ultrafast cold brewing, aiming to combine the benefits of cold brew with the convenience of faster preparation.

Existing literature highlights the increasing popularity of cold-brew coffee and its distinct chemical composition compared to hot-brewed coffee. Studies suggest that cold brewing leads to lower acidity and bitterness, making it a desirable lifestyle product. Several machines attempt to automate cold brewing, but they fail to drastically reduce the long extraction times (typically 12 hours). Previous research on LSPC focuses primarily on inorganic materials, with limited application to organic substances. Some studies have used pulsed lasers to fragment bioactive substances, demonstrating a reduction in particle size and increased bioavailability. However, the application of LSPC to coffee extraction remains unexplored. This study bridges this gap by applying LSPC to the cold-brewing process to shorten the preparation time.

Commercially roasted and ground Arabica coffee beans were used. The ps-LPP method involved irradiating a coffee powder suspension in water (1.65g coffee in 30 mL water) with a Nd-YAG laser (532nm, 10 ps pulse duration, 80kHz repetition rate, 125 µJ pulse energy) for 3 minutes. The suspension was stirred during irradiation. After irradiation, the coffee was filtered using commercially available coffee filters. For comparison, hot-brewed coffee (10g coffee in 100mL 90°C water) and cold-brewed coffee (10g coffee in 181mL water for 24 hours) were also prepared. The pH of each coffee was measured. Caffeine content was determined optically using UV-Vis spectroscopy (measuring absorbance at 273 nm after caffeine extraction with chloroform) and gravimetrically. Non-target liquid-phase analysis was performed using reversed-phase liquid chromatography coupled to high-resolution mass spectrometry (LC-MS). Analysis of volatile and semi-volatile components was conducted using in-tube extraction dynamic head-space (ITEX-DHS) followed by gas chromatography coupled to mass spectrometry (GC-MS).

The ps-LPP method resulted in a temperature increase of only 5 ± 3 °C during the 3-minute irradiation, maintaining near-room temperature conditions similar to traditional cold brewing. The pH of the ps-LPP coffee was statistically similar to cold-brewed coffee and significantly different from hot-brewed coffee, indicating lower acidity in both cold methods. While cold-brewed coffee showed the highest absolute caffeine concentration, the relative caffeine release per minute was significantly higher for the ps-LPP method (approximately 300 times higher than cold brew and three times higher than hot brew after normalizing for powder concentration, temperature, and brewing time). LC-MS analysis revealed a similar alkaloid profile in ps-LPP and cold-brewed coffee, dominated by caffeine and trigonelline. GC-MS headspace analysis showed that ps-LPP coffee retained more semi-volatile compounds like pyridine, contributing to the unique flavor profile of cold brew, unlike hot-brewed coffee which lost these compounds due to evaporation.

The results demonstrate that ps-LPP provides an effective and significantly faster method for cold-brewing coffee compared to traditional methods. The similar chemical composition between ps-LPP and conventionally cold-brewed coffee, particularly in terms of key alkaloids and semi-volatile aroma compounds, supports the potential of this method to produce high-quality cold-brew coffee. The higher relative caffeine extraction rate of the ps-LPP method highlights its efficiency. The preservation of semi-volatile compounds like pyridine suggests that this method might capture more nuanced flavor profiles characteristic of cold brew. While the higher absolute caffeine concentration in traditional cold brew might initially suggest a more bitter taste, this should be further examined considering other taste modulating factors. The slightly more basic pH of the ps-LPP and cold-brew samples could also influence the perceived taste. Further sensory evaluation will be crucial to validate this aspect.

This study demonstrates the feasibility of ultrafast cold-brewing coffee using picosecond-pulsed laser extraction. The method significantly reduces brewing time from hours to minutes while maintaining a similar chemical composition to traditional cold-brew coffee. Future research could focus on optimizing laser parameters, developing a continuous flow system for upscaling, and conducting extensive sensory evaluation to confirm taste equivalence and explore taste preferences among various methods. This technology has the potential to revolutionize cold-brew coffee production, making it more efficient and accessible.

The study used only one type of coffee bean. Further research is needed to evaluate the method's effectiveness with other bean varieties and roasting levels. While the study performed extensive chemical analysis, a comprehensive sensory evaluation involving a larger panel of participants is crucial to determine whether the taste profiles of the different brewing methods are truly equivalent. The study used commercially available filters, and the potential leaching of filter components into the final product should be further investigated.