UC Davis Seeks to Find Clarity Through White Wine's Haze

Crisp, clean, bright — all words that come to mind when thinking about white wine. Hazy? Not so much. 

White and rosé wines can become cloudy when transported in shipping containers or stored on supermarket shelves due to protein denaturation. While they are perfectly safe to drink, those murky wines tend to turn off consumers. 

“The trend of hazy wines has not taken off like hazy beer,” said Ron Runnebaum, a professor of chemical engineering and viticulture and enology at the University of California, Davis. “If the wines become hazy on the shelf, consumers will tend to avoid those wines because they think something is defective.” 

The current process for removing proteins from wine to prevent the visual impact of their denaturation is time-consuming, environmentally unfriendly and hasn’t changed in decades. In a new paper in ACS Food Science & Technology, Runnebaum and Ece Goktayoglu, a Ph.D. student in chemical engineering, describe a technique to remove proteins from white and rosé wines, offering a more efficient, faster and more sustainable way to produce wines that consumers expect. 

Proteins Can’t Take the Heat

Protein denaturation occurs when heat increases the temperature and disrupts a protein’s structure. Heat will solidify egg-white proteins, render certain vaccines ineffective and chemically reset hair’s keratin during a perm. 

For white and rosé wines, temperature fluctuations during storage and transport — conditions that are not temperature-controlled — can cause proteins to unfold and aggregate into new formations, resulting in the visible haze that deters consumers. 

“This is something that impacts the wine industry beyond just California,” Runnebaum said.

About half of all white and rosé wines worldwide require protein stability treatment. The proteins responsible for the haze are typically found in grapes commonly found in wines like chardonnay, sauvignon blanc and pinot grigio. Additionally, wine producers typically test for protein instability to predict the potential for haze formation. 

The Bentonite Problem

If protein instability is observed in the wine, producers proceed with removing the protein using bentonite, an industry standard that dates back at least a century. 

Bentonite is a negatively charged adsorbent clay that is mixed with water to make a slurry. When the slurry is mixed with wine, the bentonite binds to positively charged proteins. The bentonite-protein mixture is then removed from the wine through settling and filtration. 

This method, explains Goktayoglu, has some glaring disadvantages. The high swelling capacity of the bentonite results in up to 10% wine loss. It’s time-intensive, with settling taking days. Additional filtration is often required to remove solids from the wine, and the bentonite clay, which is one-time use, uses a significant amount of water. 

“Bentonite is a cheap clay. It’s easy to use, but you cannot reuse it, so from a sustainability point of view, you just create this huge waste that needs to be dealt with every time you treat the wine,” Goktayoglu said. “Our question was, ‘How can we create an alternative solution that does not lose any wine and is more sustainable?’”

Going With the Flow-Through System

Goktayoglu and Runnebaum turned to a non-swelling ion-exchange resin. These resins have a stable pore structure, making them incredibly durable and predictable. They are compatible with several chemicals, making them a favorite of the pharmaceutical and food science industries, and they can be cleaned and reused. 

Goktayoglu created a model wine solution, a compound that comprises the chemical components of white wine, to experiment with a flow-through system in which the wine flows through a column packed with the ion-exchange resin. The proteins in the wine bind to the resin, and the treated wine pours out the other end of the column. 

In their study, the researchers found that the resin-based system effectively removes haze-forming proteins across a range of conditions.

The flow-through system would allow producers to continuously process wine (possibly going directly to bottling). It would also minimize wine loss and eliminate the need for additional settling and filtration steps needed with the bentonite method, which often take days. It would streamline a process that has long been considered a bottleneck in production, giving producers more control and flexibility. 

“The wine’s time in the column would be on the order of minutes to maybe hours,” Runnebaum said. “With this method, you could treat wine, and it could go directly to a bottling line. Or if you had a really large tank, you don’t have to treat all 20,000 gallons anymore. Now, if you needed to meet some sales orders that were coming in, you could treat some fraction of that.” 

Using a non-swelling ion-exchange resin also offers a more sustainable alternative for the wine industry, which faces increasing pressure to reduce waste and resource use. The resin can be regenerated and reused, avoiding the solid waste generated by single-use bentonite and reducing water consumption tied to slurry preparation and cleanup. 

Lowering Costs Long Term

The material itself comes at a higher upfront cost, says Goktayoglu, but she and Runnebaum anticipate that this method will lower costs in the long-term. In fact, in addition to testing protein-unstable wines from industry partners, Goktayoglu is now working on a techno-economic analysis that quantifies the benefits of a flow-through system from the standpoints of labor, product loss, solid waste generation and water use. 

 Goktayoglu also aims to connect the treatment with the protein concentration that makes the wine unstable. 

“Our goal is not to remove all the protein — it’s insufficient to use the resin to do that,” she said. “We’re trying to find that limit of when to stop. These kinds of experiments have never been done in the industry.” 

By rethinking a century-old process, Goktayoglu and Runnebaum are opening the door to a more flexible and sustainable way of making wine that’s crisp, bright and haze-free from production to pour. – Jessica Heath, UC Davis