http://www.wine-searcher.com/m/2012/09/sulfites-in-wine
By Rebecca Gibb | Posted Tuesday, 04-Sep-2012
... Sulfur dioxide (SO2) — in the form of potassium metabisulfite — is added to most wines and many other food products for its antimicrobial and antioxidant properties. The term “sulfites” on wine labels refers mainly to sulfur dioxide, but also includes sulfurous acid and other sulfites.
But sulfur dioxide is also a natural by-product of fermentation, so it is unlikely an SO2-free wine could ever be produced. Most yeast strains yield 10–20 milligrams per liter of SO2 during fermentation, although some, such as FX10 and M69, produce significantly more than others. Without sulfur, wine is prone to oxidation and spoilage...
... What, though, is a low-sulfite wine? No legal definition exists, making “low sulfite” claims on any label hard to substantiate.
By law, at least in the United States and the European Union, bottles containing more than a meager 10 parts per million of sulfur dioxide must state they “contain sulfites.” The regulation has been in place in the United States since 1987, and in the E.U. since 2005.
In the E.U. the maximum total SO2 levels must not exceed 210 milligrams per liter in a dry white wine and 160 milligrams per liter in a red wine. The latter level is lower because the tannins in wine are a natural preservative, reducing the need for sulfites.
However, sulfur levels need to be higher in sweet wines because sulfur is eager to bind with the sugar. Once it is “bound,” it ceases to be useful as an antioxidant and antimicrobial, necessitating the use of added sulfites. In addition, sweet wines produced from grapes attacked by noble rot, or botrytis, contain the enzyme laccase, which promotes oxidation and browning of the wine, calling for even more SO2 protection.
It’s no wonder, then, that most wine producers are attached to sulfur dioxide. Not so, however, the natural wine brigade, which is having mixed success doing without added sulfur. Some, but not all, of these wines end up unintentionally fizzy, or bretty (metallic) — reeking of manure or sticking plaster.
Stellar Winery in Olifants River has successfully commercialized a “no added sulfur” range, including an
Organic Cabernet Sauvignon and a
Shiraz. Whether the wine lasts in the bottle is another matter.
Acknowledging the no-sulfur-added wines’ somewhat mixed results, the Colorado report observes that “Consumers may be actively deterred from purchasing a low-sulfite wine if they perceive that quality may suffer.” When producers forgo the use of sulfites, “there can be a higher risk of oxidation and spoilage of the wine.”
Even so, the researchers conclude that a “no added sulfites” label could be a useful way of gaining consumers’ attention. The report’s authors suggest “offering a money-back guarantee would remove the barrier to making a purchase, but it would also shift the risk to the producer.”
In Costanigro’s view, no-sulfites wine will remain a niche category. They won't be piled high at a Costco near you any time soon.