Grades of filter sheet:

Fine/sterilising filtration:
  0.5 micron: Seitz KS50 or Beco KDS (SD30); use when bottling Sparkling wine
  0.7 micron: Beco KD (KDS15); use for pre-filtration prior to bottling or after DE-filtration
  0.8 micron: Seitz KS80 or Beco KDS12

Bright/fine clarifying filtration:
    use after kieselguhr filtration, or before sterilizing filtration:-
  1.0 micron: Seitz K100 or Beco KD10
  1.5 micron: Seitz K150 or Beco BM (KD7); use after fining or centrifuging or coarse DE
  2.0 micron: Seitz K200 or Beco KD5; use after fining or centrifuging
  2.5 micron: Seitz K250 or Beco UK (KD3); use for first filtration after fermentation
  3.0 micron: Seitz K250 or Beco K2

Clarifying filtration:
    use for light red wine:-
  3.0/4.0 micron: Seitz K300 or Beco K1
  5.0/6.0 micron: Seitz K700

Coarse/rough filtration:
    use immediately after fermentation, or for dark red wine:-
  7.0/8.0 micron: Seitz K800
  9.0/10.0 micron: Seitz K900

Filter sheets of very high fine-filtration efficiency whilst always being the safest solution may suffer from early exhaustion/blocking, hence, the correct choice of filter sheet for the task is important.

Steam sterilisation:

Ideally one should use steam (saturated steam, maximum ½ bar pressure) to sterilise the filter unit, the steam must be fed in to the outlet (normally the upper connection) of the filter. 
The inlet of the filter is normally the lower connection point.
Bringing the steam in from the lower channels (inlet side) could have the effect of washing off and thereby damaging sheets on the feed side.

The bottle filler and connecting tubing must also be steam-sterilised, by connecting to the inlet of the filter. The nozzles of each filling tube must be propped open to allow steam to flow freely from them.

The condensation water accumulating in the filter should be allowed to drain off freely at the bottom, by having the drain taps slightly open.
It is important that each side-branch in the filter (pressure gauge etc) has a drain-cock through which steam can flow during sterilisation.
The thermal load during sterilisation somewhat reduces the strength of the filter sheet.
The steaming process must be carried out with the filter pack slightly loose. This not only provides space for thermal expansion but allows the free flow of condensation water in the area of the sealing edges.
All valves must be slightly open initially during the steaming process, and steam must flow for at least 20 minutes after it starts to flow out of the filler tubes.

Setting up / inserting the filter sheets between the plates:

If steam sterilisation is not available, then:-
All plates and seals must be dipped (for at least 10 seconds) in 2% Free SO2 solution.
The filter inlets/outlets should be swabbed/sprayed with 2% Free SO2 solution, or sprayed with special alcohol sterilizing spray (eg. Sterilan).

Ensure the appropriate seals are fitted to each filter plate.

A filter sheet should be inserted carefully (centrally) between each of the filter plates.
The smooth side of the sheet (printed with logo and sheet grade) is the discharge side.  
With 40 x 40cm filters (normally): starting at the input end, the smooth side (printed) must face outwards (against the filter end-plate/chamber), the other sheets are then placed alternately between the intermediate plates, so that a smooth side (printed) always faces a smooth side, and a coarse side always faces a coarse side.
There may be an even or odd number of filter plates, according to the model of filter and whether a single or double filtration (with changeover plate) is being carried out.
With 20 x 20cm filters the flow is different from normal 40 x 40cm filters: starting at the input end, the coarse side must face outwards (against the first filter plate/chamber), the other sheets are then placed alternately between the intermediate plates, so that a smooth side (printed) always faces a smooth side, and a coarse side always faces a coarse side.

When all the sheets and plates have been inserted the centre-screw-spindle is screwed in just enough to hold the 'filter pack' sufficiently firmly to stop the sheets slipping. 
Water is then poured carefully over the filter pack to thoroughly moisten the outside edges of the sheets. 

Filter rinsing:

The filter pack must then be rinsed/flushed (conditioned) in order to eliminate soluble particles and the taste of 'cardboard/paper'. To achieve this it is necessary that cold pure water flows over and through the entire filter area, from inlet to outlet, for about 20 minutes at a rate of 1½ to 2 times the filtration rate; about 56 litres/hour per sterile filter sheet used.
To achieve even greater purity a 1% citric acid solution can be circulated in order to remove acid-soluble particles prior to filtration; this should not be used for red wine filtration.
The rinsing process must be carried out with the filter pack slightly loose, to allow some free flow of water in the area of the sealing edges. When rinsing, special care must be taken to fully remove/vent the air from the filter pack. If this is not done, sludge particles deposited during filtration can be squeezed through the filter sheet with escaping gas bubbles. Vents are located at the highest points of the channels/chambers.

Procedure: use appropriate tubing to connect the pump inlet to a vat of clean water, the pump outlet to the filter inlet, and the filter outlet back to the vat of water (with the tube carefully positioned so that the bubbles do not circulate back to the inlet; direct the tube inside a jug placed under the water).
Prime the pump if necessary, switch on the pump with the bypass closed, immediately the pump starts to function - open the bypass; the pressure difference between inlet and outlet must not exceed ½ bar even momentarily. Adjust the pump bypass until the flow is as specified above, continue circulating for at least 10 minutes until the sheets are saturated with water and all air has been vented, then for a further 5 minutes with the outlet going to waste.
Gradually tighten the centre-screw-spindle sufficiently to eliminate leaks; this is easier when the pump is switched off.
Before stopping the pump always open the pump bypass so that the pressure is low.

Filtration:

The pump inlet should now be connected to the tank of wine to be filtered.
Start the pump and begin to filter slowly.
After a while examine/taste the wine from the filter outlet drain valve, do this continually until the water/wine mixture is sufficiently wine then stop the pump and direct the filter outlet to top of the source tank, re-circulate the wine to the source tank for several minutes to ensure it is homogenous; at least 30 litres should be re-circulated.
Connect the filter outlet to the bottle filler and re-start the pump; with a T-piece and two valves it is possible to redirect this without stopping the pump. Care should be taken to prevent pressure surges.
Gradually close the bypass to increase the pressure and flow rate to the required level:- 

Fine/clarifying filtration: maximum rate = 700 to 750 litres/hour/square metre of sheet;
i.e. maximum rate = 100 to 120 litres/hour/per 40 x 40cm filter sheet used, 
maximum pressure difference (inlet over outlet) = 3.0 bar. 

Sterilising filtration: maximum rate = 350 litres/hour/square metre of sheet; 
i.e. maximum rate = 56 litres/hour/per 40 x 40cm filter sheet used, 
maximum pressure difference (inlet over outlet) = 1.5 bar (preferably 1.0 bar), 
for spritzig wine the maximum should be between 0.5 and 1.0 bar. 

It is generally true that with a higher filtration rate and increasing pressure difference the danger of sludge breakthrough (and hence contamination of the filtrate) increases. 

Filter sheet regeneration:

Sterile-grade filter sheets should be used for one day only. 
Re-use/regeneration of sheets is generally only economical on a large scale. Used filter sheets can be regenerated by rinsing with water flowing in the direction of filtration, as, due to a change in the pH value and the solute balance, separated constituents (colloids and particles) are washed out of the filter sheets. 
Rinsing at a rate of 1½ to 2 times the filtration rate consecutively in three temperature ranges has proved successful; 2 minutes with cold water, 3 minutes warm rinsing at about 45°C, approx 10 minutes hot rinsing at 70-80°C at 1 to 1½ bar counter pressure. 
All rinsing and sterilizing processes must be carried out with the filter pack loosened. This not only provides space for thermal expansion but allows the free flow of water in the area of the sealing edges. 

Types of filter plate/chamber:

Noryl (steamable plastics), with plastic or stainless steel inserts 
Noval (steamable plastics), with plastic or stainless steel inserts 
Hydronalium (stove-enamel finish) 
Stainless steel Perforated Plate 
Stainless steel High efficiency Filter Chambers 

Filter seals:

In the course of time seals lose their flexibility and become brittle, and the sealing effect is unsatisfactory. Lenticular silicon seals (6mm yellow) are highly recommended for flexibility and sealing performance. 
If, because of poor seals, excessive pressure is applied to the filter pack, this reduces the free space between the filter plates/chambers. The filter sheets are compressed excessively and the filter rate is thereby reduced. 

Filter manufacturers:

Seitz: Orion, Zenit, Original: 2 outset top channels and 2 inset bottom channels

Schenk: similar to Seitz 

Strassbourger: special plates with single central channels at top and bottom 

Spagni (KTM, Vigo): special end and intermediate plates, 4 channels 

The following use the same type of plate (2 outset top and 2 outset bottom channels):- 
Friedrich Freres: 
Elva Cristal: requires special plates at each end 
Hilge: the end chambers act as end-plates, so an odd number of plates is used 
Carlsson: 
Seitz: Ariston

The importance of diaphragm pressure gauges for sterile filtration:

A simple pressure gauge consists of an internal curved Bourdon tube closed at the far end. Wine entering this hollow tube can lead to infection, it cannot be sterilized by steam because back pressure prevents steam from entering the tube. It is therefore essential that any outlet pressure gauge is of the diaphragm type, having a flexible rubber (heat sterilisable) diaphragm which transmits the pressure to the tube via high-density glycerine.

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