Promising new tech to protect grapes from smoke taint

The University of Adelaide and Peter Michael Winery are partnering to develop new technology to combat smoke taint in grapes.

Results from trials of a new smoke taint protection technology – activated carbon (AC) hoods – were presented by Professor Kerry Wilkinson from the University of Adelaide at the Australian National Wine Sector Bushfire Conference.

In early trials the AC hoods showed promising results, protecting the grapes from 97% of smoke taint.

During trials, the grape clusters were covered with a specially woven activated carbon hood that successfully trapped virtually all smoke particulates. In her presentation, Professor Wilkinson showed examples and results for some of the completed experiments that proved the effectiveness of this new technology.

Professor Wilkinson said: “We were pleased with the early results and extended those trials to a winemaking outcome that demonstrated the carbon hood to be even more promising.”

The early field trials involved the application of smoke to Semillon grapevines and showed that enclosing fruit in the activated carbon hoods prevented exposure to smoke, such that the volatile phenols measured as chemical markers of smoke taint were barely detected in protected grapes – while concentrations up to 21 ug/L were found in smoke-exposed grapes.

“Winemakers and vineyard managers have been searching for a solution to smoke exposure for several years,” said Peter Michael’s winemaker, geophysicist and oenologist, Robert Fiore.

“This new approach could be a proactive means for preventing smoke compounds from ever reaching the grapes. Much additional work is needed to make this a practical solution, but the science supports its effectiveness.”

Trials were repeated on a larger scale with Mataro grapes, to allow wines to be made and analysed. There were no significant compositional differences between the wines made with Mataro grapes enclosed in activated carbon fabric, and control wines (i.e. wines made with grapes that were not exposed to smoke).

The research was initiated by Sir Peter Michael following the devastating 2020 California fire season.

The team invites others to collaborate in this research program, including producers and manufacturers, to further develop and verify the technology.

About Peter Michael Winery

In 1982, after six years of searching for land to serve as a family retreat and home of Peter Michael Winery, Sir Peter Michael and Lady Michael purchased 630 acres of volcanic ridges on the western face of Mount St. Helena in the Knights Valley AVA of Sonoma County. Drawing inspiration from the great wineries of Burgundy and Bordeaux, the family hired like-minded viticulturists and winemakers to help them create terroir-driven, estate sauvignon blanc, chardonnay, pinot noir, and cabernet sauvignon blends that would stand the test of time.

Today, second-generation Paul Michael and his wife Emily, continue the vision adhering to the founding principles of mountain vineyards, classical winemaking, and limited production. All three estates, Knights Valley, Seaview (Sonoma Coast), and Oakville (Napa Valley), rest on steep hillsides ranging in elevation from 500 to over 2,000 feet and total 1,191 acres with only 201 acres under vine. With a commitment to sustainability, the remainder of the land is preserved as wildlife corridors and each estate carries the Fish Friendly Farming and Sustainable California Vineyard & Winery certifications. www.petermichaelwinery.com

Sir Peter Michael

Sir Peter is the founder of Micro Consultants’ Group and UEI PLC and the driving force behind a group of high-tech companies, including Cosworth Engineering and Quantel, the digital special effects company for TV and film production. The graphic-arts tool Paintbox is just one of several commercial applications his company introduced. From 1989 to 1992, Sir Peter served as CEO of Cray Electronics, and in 1992, he founded Classic FM, the UK’s first national commercial radio station with an audience of six million. Sir Peter was knighted by Queen Elizabeth in 1989 in recognition of his contributions to British industry.

Robert Fiore

Robert holds master’s degrees in geophysics from the Colorado School of Mines and viticulture and enology from the University of California, Davis. Following a successful career exploring geologic basins around the world, he turned to wine full-time and has worked at several wineries in Napa Valley including Continuum Estate, in the Côte d’Or, Burgundy at Domaine Michel Lafarge as a Confrérie des Chevaliers du Tastevin Fellowship Laureate and has produced Pinot Noir in the Sta. Rita Hills, Santa Barbara County before joining Peter Michael Winery as winemaker in March 2020.

Professor Kerry Wilkinson

Kerry is a Professor of Oenology at The University of Adelaide. Her primary research interests concern the flavour chemistry of grapes and wine, for example, the impact of bushfire smoke on grapes and wine; the improved utility of oak wood for wine maturation; and the influence of production method on the composition and sensory profiles of sparkling wine. Other areas of interest include the chemical and sensory analysis of foods and beverages, and their appeal to consumers.

Kerry completed her Ph.D. in wine science and analytical chemistry at Flinders University and The Australian Wine Research Institute. Her appointment as an academic enabled her to combine her passion for both wine education and research.

Background

Activated carbon (AC), also called activated charcoal, is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Due to its high degree of microporosity, one gram of activated carbon has a surface area in excess of 3,000 m2 (32,000 sq ft.) as determined by gas adsorption. [source: Wiki] This high adsorption attribute makes AC a highly effective filter for various industrial applications.

Application in winemaking has typically been used to adsorb off odors, flavors, or pigments before filtering and bottling.

Smoke taint in the grapes is a result of wildfires occurring during the growing season for wine grapes. Although wildfires early to mid growing season can result in tainted fruit, grapes appear to be more susceptible to adsorbing the contaminating smoke compounds later in the growing season before or during harvest.

How does a winery prevent the smoke particles from contacting the skin of the grape without hindering ripening? A 1996 study found in the Journal of the American Society for Horticultural Science concluded that grapes could in fact successfully ripen when covered at varying stages of maturation showing no negative impact on final wines. Expanding upon this research, the addition of activated carbon to the “covering” provided a natural opportunity to explore.

Following the successful field trials which showed the effectiveness of the activated carbon hoods against smoke taint markers in smoke-exposed grapes, additional research trials involving post-harvest smoke exposure of grape bunches were subsequently performed to further evaluate the efficacy of the activated carbon fabric - using dense smoke applications to test the fabric's protective capabilities. The volatile phenol concentrations detected in grapes enclosed in activated carbon fabric were ~2-3% of those measured in smoke-exposed grapes.

Similar results were observed when Mataro grapes were exposed to smoke, with and without protection from three different types of activated carbon fabric, on a scale that allowed wines to be made. Elevated volatile phenol concentrations were detected in wine made with smoke-exposed Mataro grapes, but there were no significant compositional differences between wines made with grapes enclosed in activated carbon fabric, and control wines (i.e. wines made with grapes that were not exposed to smoke).