Ultrafast extraction of cold brew coffee in a planetary rotating bed reactor: A kinetic study on the pushback effect

Abstract

Given the rising demand for cold brew coffee, innovative approaches are required to address the present difficulties in its production. This motivates the consideration of the planetary rotating bed reactor (PRBR) as a solid–liquid extraction technology. The PRBR consists of cylindrical mesh chambers that contain the solid phase and move in two superimposed rotations. This motion pattern enhances mass transfer through alternating radial forces: the pushback effect (PBE). To evaluate the utility of the PRBR and the role of PBE, we investigated the kinetics and energy demand of cold brew coffee extraction. For this purpose, we varied rotational speeds and PBE conditions in a 1 L lab‐scale reactor. Kinetics was determined by in‐line monitoring of electrical conductivity correlated with the eluate's weight‐based total dissolved solids and caffeine by high‐performance liquid chromatography. Energy consumption was derived from strain gauge torque measurements. Our findings reveal that saturation of the extraction rate with respect to the rotational speed is evident both with and without PBE. However, PBE significantly reduces extraction time by 75% while requiring 60% less mechanical energy. The fastest conditions probed 95% of the maximum extraction yield within 12 s, effectively being >99% faster than static immersion. We believe these findings, along with further procedural advantages, qualify the PRBR as a viable technology for cold brew coffee production.Practical ApplicationsThe relevance of an economical and sustainable preparation of cold brew coffee extends from the industrial to the gastronomic to the domestic environment. Challenges and limitations relate to process time, particle separation, product and extraction yield, and taste problems due to over‐extraction. The planetary rotating bed reactor (PRBR) promises to address all these issues by combining extraction and separation in a simultaneous and ultrafast process. The present study confirms the superiority of PRBR's action mechanisms in terms of rapidity and energetic efficiency for extraction. Due to the excellent scalability of both the design and the physical effect, the PRBR is intended for large‐scale production of ready‐to‐drink products and local production in coffee shops or private households. By modifying the particle feed, even continuous operation is conceivable. Further applications are, for example, dry‐hopping of beer, fast‐aging of spirits, and preparation of various liquid foods.

Toward Higher Resource Efficiency in Solid–Fluid Reactions: Dye Adsorption Study on the Planetary Rotating Bed Reactor

“… a This includes the reactor chamber speed n RC as well as systematically equivalent absolute chamber speed n RC abs . The systematic equivalence of n RC abs and n g is due to the operation of the planetary gear drive . Although the chamber rotation is opposite to that of the carrier and therefore has a negative sign, its absolute rotation in space is positive for rpm ratios ϵ of <100%.…”

“…The transparent lid plates are sealed with O-ring gaskets. The planetary gear drive (not shown) integrated in the carrier allows the chambers to rotate around their own axis while following the carrier’s rotation. , The self-rotation is defined by the speed of the chambers relative to the carrier n RC , whereas the carrier speed n c is defined as absolute in the inertial system defined by the stationary vessel. The process platform holds the two drive trains, the cylindrical 2 L reactor vessel, and electrical and hydraulic ports.…”

“…An example for such challenging particles is powdered activated carbon (PAC), used as an adsorbent for the removal of dissolved contaminants from wastewater, 15,16 e.g., dyes from effluents in the textile industry. Inspired by this, the adsorption of methylene blue (MB) onto PAC was investigated in a 2 L laboratory-scale PRBR.…”