Membrane filtration in brewing

Membrane technology has been used in the brewing and distilling industries for many years in a variety of filtration and separation applications to treat raw water for the brewing and distilling process, for clarification and to provide effective effluent treatment of wastewaters.

The technology is extensively applied in the food processing sector, from increasing product yield in cheese making and fruit juice clarification to treating processing effluents containing fats oils and greases.

A good example of simple one-step clarification is provided by a Koch ultrafiltration plant at Hazlewood Manor Brewery, Staffordshire.

Vinegar production relies on converting alcohol into acetic acid via a double fermentation process. Once the vinegar is produced, be it malt or spirit, or cider or wine, filtration removes any bacterial debris and insoluble protein, prior to bottling. Previously, this filtration had been carried out by candle filters using diatomaceous earth. The diatomaceous earth was introduced into a candle filter and acted as a restraint, removing any bacterial debris within the vinegar as it was fed through the filter.

Further clarification

For effective clarification, filtration had to be repeated several times. In addition, the reclaimed diatom-aceous earth needed to be tankered away for landfill. Under the guidance of Koch Membranes, two ultrafiltration plants were installed, one dedicated to malt vinegar and the other dedicated to spirit vinegar. Each consists of 24, hollow fibre ultrafiltration cartridges of 5 inch diameter, treating up to 15 m3/hr of vinegar — one of the largest vinegar clarification plants in the world using membrane technology.

Clarified vinegar passes to the outside of the fibre into the clear cartridge shell, while particles are retained by the membrane and are concentrated in the storage tank. The process continues until the solids in the tank need to be removed, although reverse flow and fast flush during processing aid continuous operation between cleanings.

Since installing the new ultrafiltration plant, Hazlewood Manor Brewery has found that it is consistently achieving a much cleaner product in less than half the time previously required for clarification. The need to excavate diatomaceous earth and to landfill has been eliminated.

Because of its ability to produce pure water, free of any salts and dissolved solids, reverse osmosis is increasingly being used to produce water for the brewing process. A reverse osmosis plant is enabling Tower Brewery of Bass Brewers, Tadcaster, to increase its daily utilisation of well water. The 2000 m3/day plant has been designed, installed and commissioned by ACWa Services and features RO membranes from Koch Membrane Systems.

For that fine pint of beer, primary settlement of the yeast and larger solids is preceded by filtration, either by plate and frame or rotary vacuum. Traditional methods of filtration use additives such as Isinglass, Bentonite or Keisulguhr to flocculate, coalesce or aggregate the very finely divided material in the beer that would not normally settle out or prove difficult to filter. In particular, soluble proteins may precipitate out as the beer cools, so forming a protein haze.

Efficient membranes

This is one of the key advantages of membrane technology in that the membranes will remove essentially all of the bacteria, coagulated protein, yeast, algae, moulds, spores and viral material in the raw beer (in a size range from tens of microns to sub micron). The process does not adversely affect the product flavour, clarity or head retention. At the same time, the beer will retain those components which characterise a particular product — flavour, colour, brightness and mouth-feel. These results are achievable without the use of the additives.

Membrane technology also offers a further advantage in that spent additive disposal costs are eliminated. The concentrate produced by the membrane separation process can be disposed of to animal feed.

Membrane separations are generally pressure processes. With microfiltration, ultrafiltration and nanofiltration, the pressure is used to force the liquid stream through pores in a synthetic membrane and the three categories differ in the size of the pores, which are usually asymmetrical to minimise fouling or plugging. Reverse osmosis relies on the use of a semi-permeable membrane. By applying a pressure to the concentrated solution greater than the osmotic pressure difference, pure water molecules can diffuse through the membrane, leaving any salts or dissolved solids behind in the concentrate.

The overall performance of a membrane system is determined by membrane selectivity and permeate flux, which is dependent upon the operating pressure, temperature, pH, pore size, feed composition and flow rate. Typical values of permeate flux may lie within the range 20-2000 l/m2/hr.

Membrane filtration is already a proven and accepted technique within the brewing and distilling industries. It seems likely that its application will continue to grow rapidly because of the fact that it can be used at various points within brewing and distilling processes and because it offers significant advantages over competitive technology.