As previously mentioned, it is necessary to filter the wine after cold stabilization (as well as other times I will mention later), and this must be done while the wine is still at the temperature at which it was cold stabilized. If the wine is allowed to warm up, it is entirely possible that some of the tartrate crystals will dissolve back into the wine, possibly creating an unstable wine that will drop tartrates in the bottle, thus undoing all of the work and expense done so far.
Let me start by explaining that the standard in the wine business and most commonly used filter operation is what is called a plate and frame filter. Some wineries use other types, such as diatomaceous earth filters and cross-flow filters, but the plate and frame is the mainstay. The name actually describes it. You have a stainless steel frame that holds a number of square plates in an upright position (picture an accordion file that is open at the bottom). These filters can be purchased with different numbers of plates to hold more or less filter pads. There is even one made by Buon Vino for amateur winemakers that is a table-top set-up, holding just 3 small filter pads. I would guess that the most common size in wineries is a 40 plate filter. Of course, the bigger the winery, the larger the filter they will want, or they may even have more than one type of filter.
The pads that go into these filters look like square white ceiling tiles. One side is smooth and stamped with the brand name and porosity number while the other side is rough. The wine flows through the rough side. It is important to make sure that the filter pads are inserted properly into the frame, even the little Buon Vino, because the wine flows down one side and across the filter pads to the other side and comes out the outlet to the tank. If the pads are facing the wrong way, the wine will simply stop flowing through the filter when you pump it in. One of the pumps commonly used for transferring wine in the winery can be used to feed the wine into the filter, but it must be what is considered a high pressure pump.
The pads are alternated with the printed side facing toward the one end for the first pad (as shown in the information that comes with the filter) and then the next one is turned the opposite direction. This process continues until the filter is full. The last filter pad will end up facing the same direction as the first filter pad. At this stage of the winemaking/filtration process, a coarse filter is needed as the wine is young and probably hazy, with many yeast particles and fermentation debris still in it. You want to clean it up without clogging up the filter.
From my experience, most winemakers have a favorite brand of filter pad that they use, and there are many from which to choose. Generally, this comes from the fact that various brands have been tried and one worked the best for that particular winemaker and the type of wine he/she makes. My favorite is from a company called Begerow and I generally use three different pore sizes over the life of a white wine. At this stage, I will be using the BECO KD-3, which is listed as a 5.0 to 12.0 micron range. Just to put that in perspective, my final pad filtration on my white wine will be with a pad rated at 0.1 to 0.3 microns.
Preparation of the filter and pads is crucial to the quality of the wine, whether you are using a large plate and frame filter or a table top Buon Vino. My next post will cover this part of the operation.