(Wines&Vines) - A micron-thin membrane may be the key that locks the door on wine aromas.

Three years of trials with a polyvinylamine membrane have produced positive results for Dr. Dick Jones, a former professor of pulmonary medicine from the University of Alberta who has lived in Naramata since 2005.

An amateur winemaker, Jones enjoyed the aroma Pinot Gris gave off during fermentation—but then his scientific training kicked in, and he realized that what he smelled in today’s ferment would be gone in tomorrow’s wine.

“I thought, ‘Man, I’m going to make a great Pinot Gris,’ and then I realized that everything I was smelling that smelled so good was leaving the wine,” he told Wines & Vines. “I knew right away what had to be done: I had to selectively get rid of the carbon dioxide but leave the aroma.”

Jones began searching for a membrane that would retain the wine’s aromatic esters while allowing the carbon dioxide to pass. Ideally, it would withstand the heat of fermentation while working with atmospheric pressure, eliminating the need for hefty compressors or vacuum pumps.  

However, there was nothing readily available off the shelf. R

eading through scientific publications one evening, Jones came across a report that Dr. May-Britt Hägg, a chemical engineer at the Norwegian University of Science and Technology in Trondheim, Norway, published regarding a membrane she had developed to scrub emissions from coal-fired power plants.

The two corresponded, and in 2014 Jones used a simple membrane with a surface area of about a quarter-meter on 25-liter trial batches of Pinot Gris and Gamay wines.

The results were presented to a tasting panel of 10 winemakers, sommeliers and chefs convened with the assistance of Paul Gardner and Julie Rennie, owners of Pentâge Winery on the Skaha Bluffs in Penticton, B.C.

“They rated the experimental wine better than the control wine…to the tune of somewhere around 15% overall,” Jones said.

Samples were then sent to the UBC Wine Research Centre in Vancouver, B.C. Analysis via gas chromatograph and other equipment determined that concentrations of the ethyl and acetate esters fundamental to wine aroma were significantly higher. Concentrations in the Gamay wine, which had the membrane present throughout fermentation, were 66% higher, while the Pinot Gris, which had the membrane present only during the peak day of fermentation, saw ester concentrations 23% higher than in the control batch.

How it works

The membrane’s success is a matter of equilibrium.

“These aroma compounds are volatile, and they will leave the wine and go into the headspace if the headspace concentration is low,” Jones explained. “And of course, headspace concentration is low because CO2 keeps pushing them out.”

By allowing the carbon dioxide to pass, the membrane enables a higher concentration of volatile aroma compounds in the headspace of the wine. This establishes a more even distribution of the compounds throughout the tank, both in the fermenting juice and the headspace.

“What I’m doing is keeping the headspace concentration high by not letting the aroma out but selectively letting the CO2 out,” Jones said. “So the aroma analysis showed big increases in the aromatics of the experimental wines.”

The membrane itself is a thin coat of polyvinylamine that sits on a porous sheet of polysulfone, which serves as a supporting structure. (The membrane needs all the support it can get: at 1 millionth of a meter (1 micron), it’s seven times thinner than a red blood cell.

But by preserving the life-blood of the wines, its impact could belie its small size.

Gardner, who volunteered a 1,000-liter tank containing 700 liters of Pinot Gris from the 2015 harvest for the latest trial, said the membrane stands to be an efficient means of producing wines that stand out in the market.

While a variety of strategies have been used to date to retain aroma—from cold ferments to reverse-osmosis systems—all are costly and time-consuming.

“We basically all try to do cold ferments, we’ve pitched less yeast a couple of times,” he said. “It takes maybe three, four weeks to ferment. The problem is, that’s a luxury many wineries can’t afford, and if you don’t have to do that, why do it?”

Moreover, cold ferments, don’t always extract as much from the grapes as a higher temperature ferment might. While less aroma is lost, the wines are often less complex.

By contrast, the process Jones has devised allows fermentation to proceed uninterrupted, with carbon dioxide passing off without carrying aromas with it. Gardner estimates the cost at 75 cents per bottle.