Modeling Mass and Heat Transfer in Multiphase Coffee Aroma Extraction.

David Beverly,Robert Farr,Serafim Bakalis,Peter J. Fryer,Estefanía Lopez-Quiroga,John Melrose,Sian Henson

doi:10.1021/acs.iecr.0c01153

Abstract

Instant coffee manufacture involves the aqueous extraction of soluble coffee components followed by drying to form a soluble powder. Loss of volatile aroma compounds during concentration through evaporation can lower product quality. One method of retaining aroma is to steam-strip volatiles from the coffee and add them back to a concentrated coffee solution before the final drying stage. A better understanding of the impact of process conditions on the aroma content of the stripped solution will improve product design stages. In this context, we present a multiscale model for aroma extraction describing (i) the release from the matrix, (ii) intraparticle diffusion, (iii) transfer into water and steam, and (iv) advection through the column mechanisms. Results revealed (i) the existence of three different types of compound behavior, (ii) how aroma physiochemistry determines the limiting kinetics of extraction, and (iii) that extraction for some aromas can be inhibited by the interaction with other coffee components.

Highlights

Coffee is the most popularly prepared beverage, with a global production exceeding 9.5 million tonnes of green coffee beans.[1,2] In the United Kingdom, instant coffee dominates the coffee market with a share of approximately 80%, equivalent to around 50 000 tonnes.[3]The instant coffee process begins with the roasting of green beans to develop flavor compounds[4]
The extraction problem formed by eqs 1−34 was solved using a self-developed one-dimensional forward time centered space (FTCS) finite difference (FD) scheme, which was implemented in MATLAB
And the binding rate constant were estimated by fitting the proposed model to the published data[18] for similar extraction systems

Summary

INTRODUCTION

Coffee is the most popularly prepared beverage, with a global production exceeding 9.5 million tonnes of green coffee beans.[1,2] In the United Kingdom, instant coffee dominates the coffee market with a share of approximately 80%, equivalent to around 50 000 tonnes.[3]. Roasted coffee beans are ground to reduce the particle size increasing the surface area and reducing closed porosity[5] and undergo multiple stages of high-temperature aqueous extraction of the soluble components This extract is dried by evaporation and spray- or freeze-drying to form a soluble powder. Several published models of essential oil distillation from plant matter describe extraction purely by fitting mass transfer coefficients.[10,20] Moroney et al.[21] modeled coffee extraction in brewing, describing the transfer between inert coffee solid matter, coffee particle (intragranular) pores, and coffee bed (intergranular) pores They define lengths of diffusion from the solid to intragranular pore and from the intragranular to intergranular pore, and use experiment-derived fitted parameters to describe these processes. The practical result should be a tool to guide process development when optimizing aroma yield, concentration, and desired sensory attributes

EXTRACTION SYSTEM

MODEL FORMULATION

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES

Methods