Filtering traditional wines can be done to make a wine look better. If it's a sweet wine, filtering can prevent it from continuing to ferment after you cork it. There are numerous commercial wine filtering systems, some quite expensive. How to adapt commercial paper filters to a system you made yourself or how make your own paper wine filters comes with complications.
Types of wines
Commercial red wines are usually fermented until they are dry, meaning yeast in the bottle turns the sugar into alcohol. During this process some sediment is left at the bottom of the bottle. Connoisseurs expect this. Slightly sweet wine is sometimes passed through micro-pore filters to remove yeast cells, preventing continued fermentation and loss of sugar. This keeps the wine sweet. Wines made from mangoes, apples, pears, peaches and other juices are usually called fruit wines. Fruit wines often contain more sediments than wine made from grape juice, and therefore have different filtering needs.
The two reasons for filtering wine that you make yourself are to remove the yeast so you can drink it soon after it has ceased fermenting, and to have a 100 per cent clear wine for exhibiting. Most people argue that filtering somehow changes a wine's "character," but most people can't tell the difference. If you make homemade wine, you can rack your wine. That is, to let all the sediments settle to the bottom of the jar, after which you siphon off the clear wine from the top. Racking is time-consuming and takes work. Sometimes wines refuse to clear, even after months of storage. If your white wines have been properly racked, and you don't worry about sediment at the bottom, you might not have to filter those either. Commercial winemakers sometimes filter their wine through a thick layer of cellulose powder, diatomaceous earth, or Perlite to capture and remove small particles. They also force their wine through thin films of plastic polymer with tiny holes.
Adapting commercial paper filters
If you are a home wine maker, you may need to buy commercial paper filters and trim them to fit your filtering apparatus. To do that, you need to understand how paper filters are rated and how they are used. A GF1 paper filter will partly filter out everything in the range of two to seven microns (0.00007 to 0.00028 inches). 'GF' stands for General Factor; a micron is one millionth of a metre. All particles smaller than two microns (0.00007 inches) will pass through this filter. It will block everything larger than seven microns (0.00028 inches). A GF3 paper filter will partly screen everything from one to four microns (0.000035 to 0.00015 inches). A GF5 has a useful filtering range of .4 to .6 microns (0.00015 to 0.00024 inches). If your wine is already clear, go straight to GF3 filters, which commercial winemakers use to give blush wines and white wines brilliant clarity. The GF5 filter blocks all microbes, even bacteria, ensuring that a bottle of wine will be as stable as possible. Using these filters isn't practical with most homemade wine filtering equipment.
Making paper filters
Commercial grade filters are not needed to make clear wine, the usual object of home wine makers. For low budget or low-volume home wine makers and those making fruit wine, there is still a place for ingenuity and using paper to filter your wine. Use cheese cloth or nylon bags to strain out solid fruits before you filter. You can use coffee filters for your own homemade filtering system, but coffee filters alone clog up easily. Start with paper towels to get out heavy gunk then switch to coffee filters to remove fine particles. You might have to pass your wine through the paper towels several times before it is ready for coffee filters. Use these paper filters to clear your fruit wine both before and after it has aged.