Application of nanofiltration for coffee extract concentration

Currently it is very important that good-quality products are produced at an adequate price. In the case of instant coffee there are several production technologies. Some of these technologies do not provide good quality, and others — while the quality of the product is good — the cost is too high and needs to be reduced. As it is well known from the literature, the organics rejection of nanofiltration (NF) membranes should be very high. The aim of this work was to find a suitable NF membrane for coffee extract concentration running at optimal operation parameters which conform to given experimental conditions and to check the economical efficiency of the process compared to reverse osmosis (RO). In these experiments the filterability of the coffee extract was investigated on a laboratory-scale crossflow NF apparatus using a flat-sheet NF-45 type membrane. The influence of process parameters (recirculation flow rate, pressure, temperature) on the permeate flux and total solid rejection was investigated. The experimental data were modeled by using Rautenbach’s osmotic pressure model. The cost estimation of the NF and the RO was also made. With using NF the investment (lower applied pressure, higher flux) and operation costs (lower pressure) of the equipment can be reduced compared to RO.

On the basis of the measurement data, we found that NF can be used instead of RO. The concentration of the coffee extract could be completed on the basis of the optimal operation parameters (recirculation flow rate, temperature, pressure), which conform to given experimental conditions. After the concentration the total dry solid content of the concentrate was determined (it changed from 10.3 g/l to 45.0 g/l). The total solid rejection of the NF membrane was 98.75%. The osmosis-model is able to describe the process, and with it the industrial-size membrane can be calculated. On the basis of the cost estimation, it is seen that the costs of NF are lower than RO and that NF is as effective as RO for coffee extraction. A cleaner technology can be created and the environmental effects of the process can be reduced. These experiments are the first steps of a larger and future experiment that will contain the analytical testing and organoleptic evaluation of the coffee extract.