Reverse Osmosis (RO) is a vital part of the water treatment process, but are you aware of its growing use in the world of winemaking? While not in widespread use, the RO technology has proven to be a valuable tool and viable option for winemakers dealing with changing climates, uneven harvests, or achieving the desired taste profile in the bottled product.
While water treatment facilities utilize RO to remove contaminants and waste, wineries use RO to concentrate the juice, leading to fuller flavors and bigger-bodied wines. Critics of the technique comment that the use of RO amounts to interference in the natural winemaking process and expression of the wine’s terroir, while proponents cite the consistency of product quality and flavor profile achieved.
At a winery in Virginia, I had the unique opportunity to observe and be part of the only team in the region that operated a Reverse Osmosis system, contracting exclusively for the regional wine industry. Rather than a skid array of RO filters commonly used in the water treatment industry, the RO equipment we used consisted of a single filter, allowing the team to transport the equipment to different locations with flexibility and relative ease.
Role of Reverse Osmosis in Modern Winemaking
Winemaker Clark Smith, a pioneer in the industry, helped introduce the process of Reverse Osmosis as a valuable tool for winemakers. The controlled process ensures consistent quality and allows for targeted modifications to meet specific stylistic goals. Today, this technique is used regularly in the United States, and there are roughly 60 RO filtering systems being used by wineries in Europe, with a top House in Bordeaux among them.
The primary reasons winemakers use Reverse Osmosis include reducing alcohol content, lowering volatile acidity, and concentrating grape must—all of which contribute to producing a more balanced and enjoyable wine.
Alcohol Reduction
In some regions, particularly those with hot climates, grapes can overripen, leading to wines with excessively high alcohol levels. High alcohol can throw off the balance of a wine, masking its fruit flavors and making it taste "hot" or harsh. RO can be used to remove a portion of the alcohol, bringing it down to a more desirable level.
Using a cross-flow filter, the wine is separated into two streams: Permeate (lower alcohol) and Retentate (higher alcohol). The Permeate is collected until the target alcohol reduction is achieved, at which point it can be replaced with distilled water. The reduction of alcohol percentage can then be calculated and adjusted to the desired level.
Volatile Acidity Reduction
A similar filtration process is employed for Volatile Acidity (VA) reduction. The Permeate, containing water, alcohol, and acetic acid, is channeled through a pH column and a VA resin column. The pH column optimizes the removal of acetic acid, which is then bound by the VA resin in the second column. The resulting water and alcohol are recombined with the original wine and the resulting reduction is dependent upon the volume of the wine processed.
Concentration of Must
In cooler regions, grapes may also struggle to ripen fully, resulting in wines that lack concentration and flavor intensity. RO can be used to remove excess water from the grape must (unfermented grape juice), thereby concentrating the sugars, acids, and flavor compounds. This can lead to wines with greater body, complexity, and aging potential.
Pros and Cons
While Reverse Osmosis can be a valuable tool for winemakers, its use is not without controversy, with some arguing that it can strip wines of their unique character and terroir expression. Many believe that removing undesirable elements from a wine also risks taking away unique and desirable characteristics.
Proponents of RO argue that it allows winemakers to adapt to changing climate conditions and produce wines that meet consumer preferences for balance and drinkability, resulting in consistency of product, ideal for mass markets. They also point out that RO is a precise and controlled process that can be used judiciously to enhance, rather than detract from, wine quality.
The Future of Reverse Osmosis in Winemaking
By helping to reduce volatile acidity and lower excessive alcohol levels in wines, RO filtering has gained wider acceptance in the winemaking process. These techniques enable precise adjustments to wine composition, enhancing balance and drinkability while preserving individual wine character.
As climate change continues to affect the wine industry, Reverse Osmosis may become an increasingly important tool for winemakers. So, the next time you enjoy a glass of wine, you may be sipping the result of the same technology used to provide clean drinking water—refined to help create more balanced and delicious wines.
Written by: Bryan Winfrey, Search Consultant at Hunter Crown, LLC
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