Food industry is a fast-changing business. High quality has become one of the key factors, especially for production of premium instant coffee. To create new, innovative products, requirements for the products as for example higher nutritional benefits or also more consumer-friendly handling are changing. Reconstitution of the coffee powder is one of these key attributes. Reconstitution must be rapid and the powder must dissolve instantly without any particle residuals. One Ap-proach, which will be focused on during this work, is to improve reconstitution by control of pore structure in instant coffee powder.
Improvement of drying and reconstitution kinetics of instant coffee powder by variating the pore structure.
The structure is created by controlling the ice structure during the freezing step of high concentrated coffee extract (Figure 3). A scraped surface heat exchanger is used to create different sizes of ice crystals by varying the process parameters. In a second step the ice slurry is hardened in a freezer and ground cold to commercial coffee size. The frozen granules are dried in the freeze dry-er where most of the water is removed in two steps under vacuum: During the primary drying ice crystals are sublimating, during the second step the adsorbed residual moisture is removed. The dried material is characterized by microscopy and mercury porosimetry to determine the pore size distribution. In a last step reconstitution kinetics are measured under controlled conditions to measure the impact of pore structure on reconstitution kinetics.
The process chain was successfully established. Creation of structures with different pore size distributions are successfully applied (Figure 4). In a next step the influence of different process conditions in the scraped surface heat exchanger on the pore structure will be investigated.
Nestlé Research Center, Lausanne, Switzerland
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