By: Thomas J. Payette, Winemaking Consultant
Filtration can be a critical aspect of fine wine making. Many winemakers work hard getting their wines opulently clear, but do they understand what is happening and what the choices of filtration are?
The Webster definition of “filter” is “A device containing a porous substance through which a liquid or gas can be passed to separate out suspended matter.” In most instances, filtration is the physical removal of solid objects, in suspension, by way of a mechanical means. In most cases, wine is forced through a filter media by way of positive pressure. In only one case the author is aware a vacuum is used.
The Typical Types of Filtration are…
Plate and Frame: One of the more common types of filtration one finds in the wine industry for large particle removal and its versatility by way of changing the filter pads to remove very small particle sizes down to 0.45 microns and potentially smaller. Pads, mostly cellulose today, are installed between frames in the proper orientation and the unit is tightened down on the filter pads so leaking is minimal. This type of filter uses positive pressure from a pump to physically push the wine through the filter pads. A very versatile piece of equipment for the winery after the wine has been allowed to settle reasonably well in the wine vessels. For “dirtier wines” and fast to market wines one may consider the DE filter descried below.
Diatomaceous Earth (DE): A Diatomaceous Earth filter uses diatomaceous earth, similar to what one may find used in the swimming pool industry, as the filter media. Stainless steel “screens” hold the DE on them, while positive pressure is exerted continuously, holding the DE in place to be the filter media. A dosing pump will systematically add extra DE to the wine, upstream of the filter screens, to continuously add to the filter media. If run properly, one may be able to filter substantial amounts of wine with few to no tear downs or much clogging. The flow rates, if operated properly, will not be reduced significantly. These filters do take time to learn how to run them and the media (DE) has some health concerns during its storage, use and as a waste product filter after use. Please investigate these issues to make an informed decision should the choice to move forward with these types of units exist.
Lees Press: This may be considered the largest pore size filter and most frequently used with juices during crush. Diatomaceous Earth may be added to juice or wine lees and forced through canvass filter sheets. Often the results are that muddy looking juices filter opulently clear, before fermentation, to provide a large economic return. It is estimated that a winery of 3,000 cases or more of wine, made from white grapes, will benefit from these types of filters and pay for themselves, with proper use, within the first two years easily. The cost of the DE is minimal and the rewards are great. The one slight disadvantage is that this becomes another process to do during harvest when many processes require the winemaker’s attention. If managed properly it becomes easily juggled during harvest and worth the winemaker’s while not to mention the wineries’ financial bottom line. This filter has the same DE health concerns mentioned above.
Cartridge: These can range from large pore sizes to minute pore sizes and their surface area is not as easily adjusted as one may be able to do with a plate and frame as mentioned above. This may be the only filter a smaller winery may have but as volumes get larger in the cellar one rapidly outgrows this type of filtration. Success is very much dependent on the style and age of the wine. One advantage these filters have added to the industry is the ability to do a final polished filtration during bottling. Because these filters are made largely for the pharmaceutical industry and have significant cost, it is recommended wineries obtain them for bottling and to re-sterilize them before each use. This feature provides the most effective use of these filters and makes them highly cost effective. They should also be evaluated for their integrity if one is using them for “sterile bottling” as the industry knows it today.
Vacuum Drum: Typically used very much like the lees filter press above for “dirtier juices.” For this reason, vacuum drum filters are used mostly with lees, raw juices, and racking bottoms. This mode of action has a coating of Diatomaceous Earth on a large drum that spins while partially submerged in the liquid. The liquid is sucked through the DE coating on the drum. As the drum spins a large blade or knife cuts off the clogged portion of the DE revealing a clean layer of DE for filtration as the drum continues to spin into the juice or wine for uninterrupted continuous filtration. The clean juice or wine after filtration exits the drum by way of a central tube in the center of the drum. This filter has the same DE health concerns mentioned above.
Cross-flow: Another up-and-coming filtration option for the wine maker. It is sophisticated and proving very promising while becoming a potential mainstay in the industry. In this case the filtrate and the filter media are moving in opposite directions, not perpendicular as in most other cases, while crossing over a barrier from one wine media to another. The unfiltered wine continues to wash away the solids, known as the retentate, from the porous membrane. To continue to be current on this topic one should contact their sales representative. Crossflow is especially useful for fruit wines, and it has no expendables such as DE or filter pads with little waste other than the solids that were removed. From blind tasting trials the results of this filtration are often equal to other methods but not superior.
Centrifuge: Worth mentioning, briefly, in this segment because it does offer clarification to a wine or juice by way of spinning the liquid, magnifying gravity, and forcing the particles out of solution. This is not a filtration but it does offer a means to reduce solids, including yeast and bacteria, from the wine or juice.
Every winemaker struggles with the question of how much one should filter and how tight of a pore size should be achieved. Once the winemaker stands at the filter and an assessment is done, as a before and after application, one understands certain parts of the wine dissociate and/or become lost. In some cases, this is temporary and in other cases this is permanent. On the contrary, however, some wines “clean up” after filtration. The wines become cleaner and purer tasting with more opulent clarity to the aroma and mouth feel.
The pore size is often determined by analytical review linked back to bacteria and or yeast. If a wine has not undergone a malo-lactic fermentation to completion most winemakers will use a 0.45 micron rated absolute filtration. Absolute means all particles of that size or larger will be removed if operated properly. If a wine has a residual fermentable sugar remaining many wine makers will once again use the 0.45 micron rated “sterile filter.” Dry wines having gone through a complete malo-lactic fermentation will offer a potential to review a larger pore size filtration.
This is often desired because many winemakers feel it leaves more in the wine and therefore it is more pleasing to the consumer. In many cases, a dry wine with a complete malo-lactic will only need a filtration down to 0.80 microns. In this case, the winemaker is targeting the next largest potential threat and that may be Brettanomyces. (Some more recent research has shown this may not be “absolute” at 0.80 micron and that a 0.65 micron may be needed).
Caution: Many winemakers try their best to filter as little as possible and often with positive results. Some go as far as no filtration with success. The reader should be aware that a wine could go bad if no filtration is used and certain microbial risks are very large. A wine that goes bad “on the consumer’s shelf” will offer a new meaning to most winemakers and their increasing desires to filter in the future if the problem is the result of a lack of filtration.
Keep in mind to balance the possible brand damage against the safety of proper filtration.
Filtration is a wonderful tool that previous winemaking generations were not fortunate enough to have. Filtration is the number one tool to decrease cross-contamination in the wine cellar because each microbe must have an origination point.
Filtration has been one of the best industry advancements for the winemaker because a certain amount of predictive control is placed in the winemaker’s hands as a tool allowing them to use less or fewer chemicals for the wine’s preservation.
Overall, filtration has enhanced wine quality to the consumer because fewer wines become spoiled after bottling. Think of filtration in terms of bacteria/yeast removal and less for clarification; yet, it will assist both.
References:
Amerine, M.A., Berg, H.W., Cruess,W.V. 1972. The Technology of Wine Making
Dharmadhikari, M.R., Wilker, K.L. 2001. Micro Vinification.
Zoecklein, B.W., Fugelsang, K.C., Gump, B.H., and Nury, F.S. 1999. Wine Analysis and Production
Verbal discussion with Mr. Jacques Boissenot, Mr. Jacques Recht, Dr. Ralf Kunkee, Mr. Joachim Hollerith and Mr. Chris Johnson.
