Abstract
The investigations presented have concentrated upon the development of a constant flux crossflow filtration system to investigate the fouling by beer solids on microfiltration membranes. Existence of a critical flux at an economically viable level could not be confirmed by experimentation. Flux was varied over the range 50 litres m-2 hr-1 to 200 litres m-2 hr-1, at crossflow velocities of 0.38 m s-1 and 1.50 m s-1. All filtrations were carried out using a lager-type beer obtained from a local brewery. This beer had been centrifuged and cold-conditioned at the brewery. Where appropriate, to investigate the influence of yeast, yeast was dosed back into the feed beer. All filtrations were carried out at 5°C. Fouling layers removed from the polymeric membranes employed in all the filtrations were very similar to those found when filtering the same beer in a constant pressure mode of operation using a stirred cell [1, 2]. Carbohydrate, protein and polyphenol were all quantified in the removed fouling layers. Carbohydrate was found in the most significant quantities, typically making up 55% to 65% of the total weight of the fouling layer. Protein and polyphenol were present in much smaller quantities but typically their proportion in the fouling layer was greater than that found in their corresponding feed beer. This suggested that protein and polyphenol were deposited preferentially at the membrane surface. Crossflow velocity, flux, yeast and membrane pore size all had little influence on the composition of the fouling layers over the ranges investigated. To investigate layer development, fouling layers were removed and analysed after a range of filtration steps. The proportions of carbohydrate and polyphenol found in the fouling layer did not vary significantly as the layer developed. The proportion of protein in the layer increased as the fouling layer developed. A determining step in fouling deposition could not be confirmed by quantitative foulant analysis. In all experiments, the quality of the filtrate, determined through Photon Correlation Spectroscopy (PCS) was comparable to that achieved through filtration of the same beer using conventional diatomaceous earth filtration technologies.