Europeans testing sulphite free preservation
Sulphites are formed when sulphur dioxide, added to most of the world's wine as an antimicrobial agent and antioxidant, reacts with water molecules.
Referred to as "cold pasteurization," since it spares heat-sensitive ingredients, the new, non-thermal process involves pressure-change technology (PCT) developed by a Dresden company for fruit juice.
This technology is now being applied to wine by an eight-member consortium from five European countries in a project funded by the European Union (EU).
In PCT, a chemically inert gas such as nitrogen or argon is dissolved in wine at a high pressure of up to 500 bar, explained Ana Lucia Vasquez-Caicedo, a food technologist at the Stuttgart-based Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB), a leading member of the consortium.
The gas diffuses into microbial cells, and sudden depressurization to atmospheric pressure causes it to expand and the cells to burst. Having returned to a gaseous state, the gas is then removed.
The researchers now plan to build a mobile PCT plant that can be tested on-site at various wineries. Vasquez-Caicedo said PCT was meant to give European vintners an alternative to the current practice of adding sulphur dioxide to prevent spoilage.
In the EU, sulphites must be declared as an ingredient on wine labels, and limits on sulphites have been lowered. Sulphur dioxide extends a wine's shelf live in two ways.
First, it inhibits the development of microorganisms such as unwanted yeasts, acetic acid bacteria and lactic acid bacteria. And second, its antioxidant properties safeguard the wine's delicate flavours and protect it against browning.
Since sweet wines are more susceptible to refermentation than dry ones, they require more sulphur dioxide, Vasquez-Caicedo said. Noting that alternative preservation methods were controversial in the wine industry, she stressed that the development of PCT wasn't part of an anti-sulphite campaign.
"Every vintner has his or her own production process," she said.
Before PCT can be applied on an industrial scale, it must be tested and approved by the Paris-based International Organization of Vine and Wine.