All of the things we are going to do now are being done to remove the papery or cardboard taste from the filter pads. If this is not done before running the wine through the filter, the wine will pick up those flavors and be ruined. It has never ceased to amaze me that some commercial winemakers apparently do not do this first step (or don't do it sufficiently), as evidenced by some of the wines I have tasted in competitions that have the paper filter taste. Even more amazing than that is the fact that these producers can't taste it in their wine and realize there is something wrong, and even go so far as to enter those wines in competition!
The first thing that has to be done is to run some water through the filter. This generally takes quite a bit of water. If we are talking about a 40 plate filter and it is fully loaded, it will take 10 or more gallons of water before you have water coming out in good flow from the outlet. Once I do, I generally will run another 5 gallons or so through. After the water, I send through a citric acid solution. The filter pad people will tell you that you only need to mix citric acid with water and run it through the filter pads. But I like to make a strong solution of both citric acid and metabisulfite to run through. I feel like this helps to sterilize those nooks and crannies in the plates that can harbor bacteria and such. So I mix up a 5 gallon bucket of water with a cup of citric acid and an ounce of metabisulfite. As this is being pumped into the filter, I continuously run water into the bucket, thinning out, so to speak, the solution. This way you don't have to have several buckets of solution. Eventually the water in the bucket becomes neutral tasting and it is time to send water after the citric acid solution to get it out of the filter pads. When the water tastes good coming from the outlet, you are done and it is time to drain the water out of the filter.
Now this is the tricky part to explain if you have not seen one of these filters (hopefully the following pictures will help). You always put the water/solution/water into the filter in a certain order so all of the filter pads get properly wet and the solution hits every one, as well as rinsing them all with the water in the end. My filter has one inlet with a spigot, and two outlets, each with spigots.
The reason I have two outlets is that my filter is capable of doing a dual filtration, using two different micron size pads with a crossover plate. That is a subject for a different post. But the idea is to make sure what you are putting into the filter comes out of each of these locations in order. So I close off both outlet valves and spigots and leave open only the inlet valve (of course, because how else would the water get in?), and the spigot that is on the inlet. As the water fills the filter, the air is pushed out through the spigot. When all the air is out and the water starts to come out of the spigot, it is time to close it and open the next spigot, which in my case, is the one at the back of the filter. When water comes out of there, I open the last spigot, and close the second one. When water flows freely from that spigot, I open the actual final outlet. In this way, all the air is removed and all parts of the filter pads will be wet. The next step, of course, is to send the citric solution through. The whole process is repeated again. Close off the outlet valves and spigots and once again open up the spigot on the inlet. I open and close each spigot and valve in succession as described above for the water, this time switching when I can taste the citric solution at each point. The last to go through then is the water, once again in the same way, except that this time I am tasting for clean water (no hint of citric acid).
In order to get as much water out of the filter as possible, there is generally a lower small spigot that you can open and drain. Many winemakers simply start their wine into the filter and push the water out, watching for the wine and tasting until they are secure in the fact that what is coming out is not watered down. I had an apparatus made that I can connect to the hose on my CO2 cylinder that connects to the filter and then I use the CO2 to push as much of the water out as I can. I feel this wastes less wine (which would get mixed with the water), and improves the overall quality of my wine.
So now I am ready to filter my wine. Once again, the procedure is exactly the same as when I first put the water through. Opening the valves and spigots in the correct order, pushing all the air out of the filter, filling it with wine, tasting it as it comes through the outlet to make sure there is no water mix, and finally hooking the outlet hose up to the receiving tank. Now we will all just pray my filters don't clog up and all of the wine can get filtered in a single run, because, as you can see, the set up is a very time consuming process.