Cold pasteurisation to replace sulfites in wine?

Sulfur dioxide added during the winemaking process prevents wine spoilage, but can also cause allergic reactions - including asthma - in some consumers. In recent years, permitted sulfite limits have been reduced in the EU and sulfites must be declared on the label.

Conventional alternative physical preservation methods such as filtration are not entirely suitable for wine as they remove colour and certain flavours. Other methods which operate at high temperatures, such as pasteurisation, destroy heat-sensitive ingredients that contribute to the wine’s flavour and aroma.

German company Edecto has developed and patented a ‘cold pasteurisation’ method that preserves liquid products at moderate temperatures.

“The physical process has effects similar to those of sulfurisation of the wine: growth of microorganisms is prevented because the cells are mechanically disrupted. In addition, the protective atmosphere of an inert gas decreases oxidation reactions, so drinks are stabilised,” explained Edith Klingner, a physicist at Edecto, who coordinates the EU-funded project PreserveWine-DEMO.

The first PreserveWine project saw Edecto and other international partners investigating whether the new method can also be applied to wine.

At the Fraunhofer IGB a batch plant was modified and, on the basis of initial results, a continuous plant was developed and built. The TÜV-approved pilot plant can treat up to 120 litres of wine per hour at a pressure of 250 to 500 bar and at temperatures below 40°C. The results are promising for the treatment of white wine as well as red wine.

“Unwanted oxidising enzymes are inactivated, while neither temperature-sensitive ingredients nor colour and taste are altered by the treatment,” said Dr Ana Lucía Vásquez-Caicedo, food technologist and group manager at the Fraunhofer IGB.

In the pressure change technology a chemically inert gas, such as nitrogen or argon, is dissolved at high pressure in the liquid to be preserved. When the liquid is exposed to a high pressure of up to 500 bar, the solubility of the gas increases in the liquid. As a result, the dissolved gas also diffuses into the microbial cells. When the pressure is finally abruptly decreased, the gas expands - even within the cells - and causes these to burst. The previously dissolved gas then goes back into the gas phase and is recovered for re-use.

“In studies at the Fraunhofer IGB and our partner institute ADERA, we have shown that the colour of the wine is maintained over time during storage in barrels or bottles. In wine tastings, we found that the taste is not affected,” said Vásquez-Caicedo.

The new preservation method can be used in different stages of wine production: after vinification (wine pressing) of white wine, after the alcoholic fermentation, after the malolactic fermentation employed mainly in red wine for acid degradation as well as when racking and filling.

A follow-up project will see the process transferred to an industrial scale. The researchers aim to build a mobile plant that can be tested on-site in a range of wineries. The consortium also hopes to ensure product quality and process feasibility, and plans to examine consumer acceptance of the new technology.