148 A S. Grandison and T.J. A. Finnigan cline. It is frequently an advantage to start the run in the dynamic mode (i.e. with water circulating prior to introduction of the feed), or with the permeate side filled with solvent While the abov ve methods of combating fouling can be ve effective. it is essential mbine them with efficient chemical cleaning procedures A characteristic of MF is that the separation may alter during processing due to fouling, such that the MF operation, in reality, becomes UF through a secondary membrane'formed at the surface of the MF membrane, consisting of macromolecules or lloids. This generally constitutes a problem. However, this property has been used to advantage in the French dairy industry for the concentration of milk. Bennassar et al (1982)described the use of the selective UF properties of the secondary membrane formed while using 0.2 um membranes. Almost total retention of milk protein was sible with this membrane 5. 3 APPLICATIONS IN THE FOOD AND BIOTECHNOLOGY INDUSTRIES MF is generally used to separate particles suspended in liquid media, and may frequently be considered as an alternative to conventional filtration or centrifugation. For industrial use the aim is usually to obtain either a clear permeate or the concentrate. Therefore most applications are either clarification, or the recovery of suspended particles such as cells or colloids, or the concentration of slurries. MF is a useful process for the treatment of fermentation broths, frequently as an alternative to centrifugation. During recovery of intracellular components, the cells can be enriched and washed by diafiltration prior to disintegration of the cells, and cell debris can be removed from the products of lysis MF membranes can be incorporated in water polishing systems as they are effective in removing suspended solids and bacteria. They may also be applied to a variety of liquid food streams, and may give the accompanying benefit of chemical and/or micro- biological stabilisation. Clarification of biochemical or microbiological reaction products or effluents is also possible. MF is a well-established laboratory technique for the production of sterile fluids without the application of heat 5.3. 1 Food industry Perhaps the majority of applications in the food industry have been in the treatment juices and beverages. As MF is a purely physical process, it can have advantages over traditional methods involving chemical additives, in terms of the quality of the product as ell as the costs of processing Finnigan and Skudder(1989)discussed the application of ceramic microfilters to the processing of beer and cider. Very good quality clear permeate was found for both products with high flux rates. Fluxes of 200-400 I m h were obtained with beer at low temperatures with no rejection of essential components. Recovery of beer from tank bottoms is also possible using ceramic MF, but this is less important in the UK now that duty is not paid at the wort stage of production Clarification and biological stabilisation of wine musts and unprocessed wine have been described. This avoids the requirement for fining and, possibly, pasteurisation. Dau et al.(1988)used membrane filters with pore size 0. 1-5 um to clarify wine preheated148 decline, It is frequently an advantage to start the run in the dynamic mode @e. with water circulating prior to introduction of the feed), or with the permeate side filled with solvent. While the above methods of combating fouling can be very effective, it is essential to combine them with efficient chemical cleaning procedures. A characteristic of MF is that the separation may alter during processing due to fouling, such that the MF operation, in reality, becomes UF through a ‘secondary membrane’ formed at the surface of the MF membrane, consisting of macromolecules or colloids. This generally constitutes a problem. However, this property has been used to advantage in the French dairy industry for the concentration of milk. Bennassar et al. (1982) described the use of the selective UF properties of the secondary membrane formed while using 0.2 pm membranes. Almost total retention of milk protein was possible with this membrane. A. S. Grandison and T. J. A. Finnigan 5.3 APPLICATIONS IN THE FOOD AND BIOTECHNOLOGY INDUSTRIES MF is generally used to separate particles suspended in liquid media, and may frequently be considered as an alternative to conventional filtration or centrifugation. For industrial use the aim is usually to obtain either a clear permeate or the concentrate. Therefore most applications are either clarification, or the recovery of suspended particles such as cells or colloids, or the concentration of slurries. MF is a useful process for the treatment of fermentation broths, frequently as an alternative to centrifugation. During recovery of intracellular components, the cells can be enriched and washed by diafiltration prior to disintegration of the cells, and cell debris can be removed from the products of lysis. MF membranes can be incorporated in water polishing systems as they are effective in removing suspended solids and bacteria. They may also be applied to a variety of liquid food streams, and may give the accompanying benefit of chemical and/or micro￾biological stabilisation. Clarification of biochemical or microbiological reaction products or effluents is also possible. MF is a well-established laboratory technique for the production of sterile fluids without the application of heat. 5.3.1 Food industry Perhaps the majority of applications in the food industry have been in the treatment of juices and beverages. As MF is a purely physical process, it can have advantages over traditional methods involving chemical additives, in terms of the quality of the product as well as the costs of processing. Finnigan and Skudder (1989) discussed the application of ceramic microfilters to the processing of beer and cider. Very good quality clear permeate was found for both products with high flux rates. Fluxes of 200-400 1 m-2 h-’ were obtained with beer at low temperatures with no rejection of essential components. Recovery of beer from tank bottoms IS also possible using ceramic MF, but this is less important in the UK now that duty is not paid at the wort stage of production. Clarification and biological stabilisation of wine musts and unprocessed wine have been described. This avoids the requirement for fining and, possibly, pasteurisation. Dau et al. (1988) used membrane filters with pore size 0.1-5 pm to clarify wine preheated to