by Nancy Vineyard and Gabe Jackson
“Microfiltration” wine filtration is a process of passing wine through media to remove particles that are suspended. The filter barrier prevents the passage of particles above a determined particle size. All microfilters are “nominal” filters not “absolute” filters, which will be defined in a bit.
Two types of microfiltration systems are well supported for home winemakers. Both require carefully choosing the correct size media porosity for the greatest effect. The current available sizes range from 0.5 micron to 8 micron. In general, 96-98% of the particles larger than the rating will be retained in the media and removed from the wine.
A cartridge system utilizes a 10” cartridge made of wound polyester/cotton string, or perforated nylon on a stainless core, which is fitted in a polycarbonate or stainless housing fitted with inlet and outlet ports. A pump moves the wine through tubing into the housing and the filter holds back particles larger than the media rating, while passing the wine out the exit tubing.
A plate/frame system similarly uses a pump for the passage of the wine, but the wine moves through a square sheet of media made of cellulose fibers with a filter aid such as perlite or diatomaceous earth plus a resin binder that adds strength to the pads. The pads are fitted between plates that are patterned to channel the wine to the outlet while the pads retain the removed particles.
It’s best to think about filtering as one tool that can be used to improve clarity and stability in wine. In small batches of wine, it is generally only used when gravity, fining and aging haven’t removed visible haze, or if laboratory analysis reports the presence of spoilage yeast or bacteria. For large batches of wine in barrels or tanks, pumping is almost always a necessity and, therefore, filtration generally becomes an easy addition to the transfer process.
To understand what is removed by filtration, keep this reference:
The micron size of some wine particles are as follows.
Tartrate Crystals: 5-500 micron, mostly fall out in cold stabilizing.
Protein Precipitates: 2-20 micron, mostly left behind during racking.
Yeast: 1-2 micron, mostly fall out after sugar is consumed and after CO2 is diminished from several rackings, but may require filtration.
Bacteria: 0.6-0.8 micron, requires filtration to remove.
Plate & Frame Systems come complete and ready to use.
The Beverage People plate filter is made by Buon Vino. It holds three pads that can process 30-45 gallons.
In addition, for larger volumes we sell a six plate plate filter produced in Italy. These both come with a pump.
Cartridge Systems Require Assembly of Assorted Parts
The cartridge filter system can process up to 150-200 gallons of wine per cartridge if the correct micron size is chosen. This system consists of several components: a Vintage Shop variable speed, self priming diaphragm pump, a 10” cartridge housing, a filter cartridge (three sizes to choose from---F10, F11, F12) and the inlet and outlets barbs with 1/2” tubing.
Buon Vino Filter Pads with Holes: 0.5 micron "Sterile", 2 micron "Polishing", and 8 micron "Coarse"
Filter Cartridges: 0.5 micron "Sterile", 1 micron "Polishing", and 3 micron "Coarse"
Italian Plate Filter Pads, Solid without Holes: 0.5 micron "Sterile", 2 micron "Polishing", and 8 micron "Coarse"
Our suppliers still call 0.5 micron filters “sterile” even though that isn’t a correct term. In practice, the wine passed through the 0.5 micron filters is as sterile as you will get in home winemaking, but these do not remove bacteria below that which means these filter media are actually nominal, not absolute. The amount of money needed to purchase an absolute filtration system isn’t even on the table for most small wineries.
What happens to a wine if the effective filtration leaves behind 2% or more of a bacteria or yeast?
In the case of a spoilage organism, like acetobacter, the wine will continue to degrade in quality during storage, because the bacteria will continue to produce some volatile acidity. Bottling soon, adding sulfite and storing cool will slow or stop the increase of volatile acidity, but there will always be a flaw in the wine flavor and aroma.
In the case of yeast, any remaining residual sugar could restart a fermentation in the bottle. Good insurance against refermentation is supplied by adding sulfite and potassium sorbate (Sorbistat) at bottling time. Use the sorbate at the recommended dosage of 1 gram per gallon, stirred into wine at bottling.
In the presence of Brettanomyces; off aromas can include cloves, barnyard, horse hair, horse sweat, plastic, Band-aids, and mousey, all good things to avoid if possible. Brett can be removed with 0.5 micron filter media, but whether or not 2% remains, the wine will already be tainted, and will not improve after removal. Look below for more information on best practices to avoid spoilage organisms.
So how is wine “ultrafiltered” (sterile/absolute)
The most common tool is a cartridge/housing configured with an absolute membrane filter. They are used on mobile bottling lines and only used when the winemaker is sure that the wine needs this final pass. Larger wineries can also use a Crossflow filter, which has media available for both microfiltration and ultrafiltration. Some of the advantages of this filter that overcome it’s very high cost include: the ability to 100% remove Brettanomyces, zero absorption into the media so no wine is lost, and single step filtration to reduce multiple run costs associated with other types of filtering.
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