Soft Drinks and Fruit Juice Filtration


Soft Drinks and Fruit Juices

The production of soft drinks involves the filtering of both sugar syrup and water used in the bottling process. The source and degree of refinement or purity of the sugar supplied for syrup making will largely determine the treatment and filtration needed. There may be as much as 0.8% by weight of impurities in unfiltered syrup and the colour requirements of the finished drink may require decolourisation of the syrup as well as filtration. Analysis of the available sugar should show the percentage purity of the sugar as well as impurity and colour levels.

Most syrups are produced using either the hot or cold method. Relatively dilute syrups are mixed at ambient temperature in a supply tank, filtered under pump pressure and hence to a holding tank. Syrup of high concentration or Brix value, will be produced by the hot process at 80 degrees C or higher, filtered and cooled as quickly as possible to avoid any bacterial growth. As the condition of the sugar will determine the degree of decolourisation and filtration needed, it is important to decide at the outset whether activated carbon treatment and any filter aid such as kieselguhr, will be necessary. This will allow the relevant filtration equipment and correct filter sheets to be specified. The expertise of Carlson's Technical Development Centre is available to help in this area. Carlson's high performance W2N support sheet is specially designed for this type of application. W2N sheets offer a number of benefits to the soft drinks manufacturer:

Because W2N sheets are manufactured from pure cellulose incorporating carefully chosen wet strength resins within the cellulose matrix, the sheet has a high wet strength and is very durable. This allows the sheet to be used time and time again, so minimising costs.

The pore size distribution of the sheet is carefully controlled so that there is even build up of the filter cake on the sheet. This ensures that filter capacity is maximised and that there is minimum risk of bleed through of even the finest of fines, whilst minimising the pressure drop through the filter.

W2N sheets are very tolerant of pressure transients during the filtration cycle because the formulation used in their manufacture, coupled with the manufacturing process produces an extremely durable yet flexible sheet.

Typically for this application, 0.5% or even more of kieselguhr is added to the syrup as a filter aid and prior to batch filtration, 500 grammes per square metre of filter plate area is applied as a pre-coat in treated water. Sugar syrup filtration flow rates vary according to conditions, e.g., viscosity and sugar quality etc. High quality, relatively dilute sugar syrup made be filtered at 950 litres per square metre per hour. On the other hand, flow rates as low as 300 litres per square metre per hour may be possible with high concentrations of syrup containing activated carbon and kieselguhr.

Carlson XE20H or XE50H sheets are normally used for polishing when no decolourisation is needed.

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