Reverse Osmosis
Wine making is a combination of traditional techniques and modern advancements. While there is always a push for minimal intervention, every once in awhile, a piece of technology comes along that is too good to ignore. Reverse Osmosis is one of those tools. The RO filtration unit is able to drastically improve wines by adjusting a few major components. Read on for a better understanding of how winemakers can use this piece of equipment to craft a better product with precision.
Reverse Osmosis:
An extremely tight filtration... with a wide variety of applications... Originally utilized in rainy areas to remove rainwater from musts,... RO is now widely used in dry areas to remove excessive alcohol, thus facilitating harvests at proper maturity... In this application, RO permeate, which contains substantially no flavor or color, is distilled to remove high-proof alcohol and then is returned to the wine. Precise alcohol levels called "sweet spots" are routinely observed, with alcohol contents within 0.1% being critical to harmonious balance. RO can also... correct volatile acidity, which occasionally occurs during elevage.
- Clark Smith, Postmodern Winemaking
Most filters used in wine making are used to clarify or microbially stabilize wine. The "clean" wine passes through the filters (referred to as permeate,) while the unwanted particles are held back by the filters (the retentate.)
Reverse Osmosis filtration (RO) is based on a unique concept. RO has the ability to separate out the water and alcohol, plus a few unwanted aroma compounds, from the rest of the wine. Due to the RO design, the permeate is the "unwanted" portion of the wine. The retentate, the solution not filtered, is the portion of wine that is wanted for the final product.
The RO filtration system (pictured above) has eight 100-dalton filters. The filters are so minuscule that they only allow a few small particles to permeate the membranes. Water, alcohol, acetic acid, and ethyl acetate are smaller than 100 daltons, and thus permeate through the filters. The remaining wine compounds are unable to pass through the small pores. The wine's color, aromas, and structural compounds remain in the retentate.
So why is this useful to wine making? There are a number of uses for RO filtration. RO can be used to adjust the alcohol levels in wine; either increase or decrease. This is accomplished by sending the permeate (the water and alcohol) to a secondary unit for distillation (pictured above.) The distillation separates the alcohol and water, and the desired components are then returned to the wine. The removal of water also acts to concentrate the retentate (flavors, color, etc.) This is particularly useful in a rainy season.
The adjustment of alcohol has proven to provide "sweet spots." Alcohol is a major component to finding balance in wine. The concept of sweet spots is based on the fact that wine can be drastically better, or worse, at certain alcohol levels. The sweet spot for alcohol can be achieved within 0.1% difference. When conducting RO, trials should first be done to fine tune the final alcohol to achieve these desired sweet spots.
Unwanted aromas can also be removed by RO. An ion exchange can be used as a secondary unit to RO. This will separate out the acetic acid and reduce the overall volatile aromas in the permeate. Another use of RO can be to reduce Brettanomyces or smoke taint aromas. An RO with slightly larger pores is necessary for this application.
So what are winemakers thinking of this piece of equipment? Generally, those who have used Reverse Osmosis have only good comments to say. However, the natural wine movement and minimalists alike will always push back on adjustments made in attempt to enhance wines. This is a great tool for winemakers, and ultimately, the customer is the only one who benefits from the high quality product.
The application of RO on wine was patented by Clark Smith, author of Postmodern Winemaking. The principals behind Postmodern Winemaking are intrinsically linked to RO. For anyone who wants to know more about RO, Clark Smith and his work are great resources.
http://whoisclarksmith.com/
http://www.vinovation.com/custequip.htm