Ozone, a sanitizing agent traditionally utilized in the wine industry to clean crush-pads and occasionally barrels, has additional benefits that few are aware of. For instance, it has been used to treat grapes, resulting in wines with less added SO2, and to alleviate vineyard bacteria that can cause stuck fermentations. According to winemakers who have tried it, ozone treatments enhance the fruity flavors in the finished wines. Currently, they are exploring whether ozone treatments can effectively clean smoke-exposed grapes before they are used in winemaking.

Ken Bernards, a consulting winemaker, was preparing for the 2017 wine grape harvest and planned to test ozone treatments before destemming a Cabernet vineyard to solve a problem. Although he was skeptical, he remained open-minded after sampling wines that had been treated with ozone in trials at a nearby winery.

It was Steve Reynolds who was utilizing it to produce wines with low levels of sulfites.

In October 2017, during the outbreak of the Tubbs Fire in Napa, Bernards aimed to expedite the fruit processing process. Upon reaching out to the equipment and processing company to cancel their experiment, the vendor proposed ozone treatments as a potential solution to mitigate smoke taint by potentially eliminating smoke taint-associated molecules.

In 2017, an experiment took an unexpected turn when Bernards observed a reduction of approximately 50% in Guaiacol molecules in Cabernet that had been treated. As a result, he decided to treat the majority of the remaining fruit with ozone towards the end of the 2017 harvest season.

According to Bernards, they were not certain about the amount of ozone they were applying, but it still had a beneficial impact. They were essentially guessing without any measurements. However, the resulting wines were of high quality and suitable for premium programs, as originally intended.

While Bernards did not conduct a controlled trial per se, they observed positive outcomes both visually and in taste tests. Analytical comparisons indicated that most of the samples treated with the post-treatment method exhibited higher levels of anthocyanin and polymeric anthocyanin compared to their pre-treated counterparts.

“While ozone treatment did result in some smoke taint in the wines, ultimately, we were able to mitigate the smoke taint using alternative methods.”

In 2020, the fire season arrived early, and during that time, a friend of Bernards, who had assisted him in importing fresh grapes from Burgundy in previous years, introduced him to Purfresh. This company provides ozone-equipped refrigerated containers to global fruit suppliers. Purfresh’s technology is utilized by fruit companies to eliminate pesticide residues and prolong the shelf life of various fruits, including avocados, blueberries, pineapples, and table grapes.

Containers were delivered by Purfresh to Porter Family Vineyards on September 16, where they treated wine grapes. Porter Family Vineyards processed the majority of their 2020 grapes using the system, and Bernards also treated lots for other wineries in Napa there in order to obtain as much data as possible. Although some of the treated wines are already dry, Bernards has a collection of samples that will be analyzed in the upcoming months. However, nothing conclusive has been determined from an analytical standpoint thus far.

In mid-to-late September of 2020, several Purfresh systems were installed in various locations, including Towle Wine Company in Sonoma Valley and Quintessa Vineyards in Napa Valley. In total, seven systems were deployed throughout Napa Valley, Sonoma Valley, and Willamette Valley.

The Innovation & Quality Conference.

Purovino supplies ozone to winemaker Robert Rex at Deerfield Ranch in Sonoma Valley, to aid in producing wines with minimal amounts of S02.

By doing so, the winery adds a degree of precision to the notion of clean wine. However, it is worth noting that the process is not employed on all the fruits harvested by the winery.

During the 2018 Innovation & Quality Conference organized by Wine Business Monthly, a trial was presented showing that Deerfield Ranch had utilized ozone to treat smoke-exposed grapes from 2017. The results revealed that there was no detectable evidence of smoke taint in the treated lots compared to the control. Moreover, the levels of phenolics and antioxidants in the treated grapes increased. At the conference, Fabio Mencarelli, a professor of postharvest technology of horticultural crops at the University of Tuscia in Italy, who had pioneered the Purovino process, was among the presenters in a session featuring top academics from around the world with expertise in smoke exposure and grapes.

According to Robert Rex, he still employs ozone in winemaking. Although the precise effect of ozone on the smoke taint-causing compounds is unclear, it appears to lower the smoke levels. However, he warned that sanitizing the fruit makes it prone to VA or contamination from other microorganisms. He emphasized the need to initiate the fermentation process promptly to prevent spoilage since the fruit is now sterilized and vulnerable.

According to Rex, ozone can be highly beneficial in cases where fruits have been damaged by molds or mildews.

According to Rex’s warning to WBM, even if ozone is used, it may not be effective when grapes are severely affected by smoke taint. In some cases, the smoke taint levels have been found to be 10 to 20 times higher than the level that can be detected by human senses. While testing has shown that ozone can remove up to 75% of the smoke taint, it may not be sufficient when dealing with such high levels. Even after removing three-quarters of the smoke taint, the remaining amount may still exceed the acceptable threshold.

Rex mentioned that although it works to a certain degree, it’s not a complete solution. Nevertheless, it is currently the most effective option available.

A Reduced Use of Sulfites

During the 2015 IQ Conference, Steve Reynolds of Reynolds Family Winery shared the findings of a trial where he utilized ozone to treat Stags Leap Merlot and Cabernet from the 2013 vintage, which were bottled in January 2015. The outcomes revealed that the method enabled him to produce a wine that was stable without the need for added sulfites. Additionally, Reynolds observed that the wines exhibited a softer character and had a more prominent fruit expression.

Pine Ridge Manages Lactobacillus Kunkeei

Michael Beaulac, the winemaker at Pine Ridge, utilized the Purovino process to overcome a stuck fermentation issue caused by the presence of Lactobacillus kunkeei, also referred to as the “ferocious lactobacilli,” in a particular vineyard. This strain was discovered by Dr. Linda Bisson from the University of California Davis Department of Viticulture and Enology and named after the late professor Ralph Kunkee. Beaulac experimented with the ozone application for three harvests and successfully resolved the stuck fermentation problem. Consequently, the vineyard was replanted, and Beaulac believes that the process has extended the vineyard’s lifespan. Beaulac shared this with Wine Business Monthly.

Applying Ozone to Grapes

According to Purfresh CEO Christian DeBlasio, the FDA has approved the use of ozone treatment on grapes, which has been shown to improve wine profile analyte measurements and reduce smoke taint impact without degrading the fruit. DeBlasio stated that there have been consistent improvements observed in these areas following ozone treatment.

Towle Merritt, the owner of Towle Wine Company, a recent wine services venture in Sonoma Valley, has collaborated with Purfresh by signing a data sharing agreement. This partnership has also been formed with Quintessa. Towle Merritt is currently involved in conducting microfermentations and collecting berry samples of Cabernet Sauvignon, both treated and untreated. He has two refrigerated containers in use and plans to experiment with two five-ton fermentation tanks to evaluate the industry’s limitations. Despite the season being late, Towle Merritt has sufficient capacity to offer the process to other interested wineries.

The ozone and air are blown upwards through the fruit from the bottom to the top of the pallets while the container is loaded and sealed. The cooled return air is directed back into the container through the front, completing the circulation.

The setup comprises a high air volume forced air chimney flow system. Standard wine field harvest bins of identical size and dimensions are enclosed with shrink-wrap, but with slots on both the sides and the bottoms, distinguishing them from regular bins.

It takes 24 hours to complete the treatment process, and a single refrigerated unit can handle 27 bins simultaneously. Potential modifications to the bin design may enable more bins to fit within a trailer, as the current bins are only a few inches too lengthy to fit beside each other in a double-wide configuration.

The expenses of treating grapes are subject to change depending on the container’s size, which could be either $10,000 or $20,000. Furthermore, the treatment’s duration also plays a role. If the aim is to optimize throughput, the cost per ton may fall around $150.

Merritt stated that reducing the 4-methylguaiacol level from four to two, or from 2.5 to 1.25, considering the abundance of smoke, would place one at the lower end of the spectrum.

According to Joe Uhr, a winemaker at Towle Wine Company, the winemaking technique used, apart from smoke exposure, is quite fascinating. He explained that the fruit is chilled and sterilized, which he considers a significant development, even during a typical year. Joe Uhr believes this technique is a game changer.