The Truth About Sulfites – Chemical Lies in Wine (First of Two Parts)
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| Winemaker weighing out sulfites for a 5,000 liter tank | |
In reality, however, nothing could be further from the truth. As is often the case when it comes to alcohol and public policy in North America, pseudoscientific groups and temperance fanatics dominate the debate. The urban myths surrounding wine are now so pervasive that cynical marketers are even using them to fob off markedly substandard wines to trend-conscious but unsuspecting Japanese consumers under the guise of a "traditional winemaking" revival. Although you'd never know it from the tone of the debate, sulfites are actually an organic compound that nature uses to prevent microbial growth. They are found on grapes, onions, garlic and many other growing plants.
Nearly all organisms, including yeasts and humans, produce sulfites as well (they are a natural byproduct of amino acid metabolism).
As chemicals go, sulfites are multitalented: In addition to preventing spoilage by inhibiting the growth of molds and bacteria, they also act as antioxidants. A cut pear left in the sun will quickly turn brown and then rot, but if first exposed to sulfur dioxide (the sulfite that is most commonly used in wine-making), it will remain brightly colored and dry without decaying. The age-old method of burning a bit of sulfur in a box filled with freshly cut fruit before setting the fruit out in the sun to dry, as in "sulfuring," is still practiced around the world today, including by my own parents in California's wine country.
It is unclear how early winemakers discovered the preservative qualities of sulfur, but it is well-documented that by 100 B.C. Roman winemakers often burned sulfur wicks inside their barrels to help prevent the wine from spoiling.
In the 16th century, Dutch traders found that only wine treated with sulfur could survive the long sea voyages without it turning to vinegar, and sulfite additions quickly became a universal winemaking tool in Europe.
Modern winemakers typically add sulfites immediately after crushing, again during barrel aging, and then once more just before bottling. Although the same form is used (potassium metabisulfite dissolved in water), the purpose at each point is different.
The initial add is usually made as the grapes are crushed, with the winemaker typically adding enough to give a final sulfur dioxide concentration in the juice of 50 ppm (parts per million). This stuns any mold and bacteria naturally found on the grapes, and allows the less sensitive wine yeasts a chance to get a substantial head start over non-wine yeasts and other noxious organisms.
As the first round of sulfites is usually absorbed during fermentation, a second round is added just before the wine is put down to age in the barrel. This helps prevent the growth of film yeasts (which occur on the surface and are responsible for sherry) and acetic bacteria, which turn wine to vinegar. Unsurprisingly, wines made without sulfite adds at the above two points are often an amalgamation of unusual odors and flavors.
The final sulfite add occurs just before bottling (typically 30 ppm-free sulfur dioxide). Over time, oxygen in the bottle combines with the wine's tannins and color compounds, and ultimately with its alcohol, resulting in a "dead" wine. Sulfites oxidize more rapidly than any other of these wine components, so in a sense they sacrifice themselves to protect the wine and extend its ageability.
Originally Published on The Japan Times ©2004  |
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