The Noble Writ: Are Sulfites Friend or Foe?
Before proceeding, it's worth noting that a not-insignificant portion of the population (estimated at about 1%) seems to have an allergic reaction to sulfites. As with most allergy symptoms, these seem to vary greatly from person to person and from exposure to exposure. However, splitting headaches, nausea and vomiting aren't common allergy symptoms. You're going to need to look for another scapegoat for those -- or admit you drank too much.
|Ben Mills, Wikimedia Commons|
|Sulfur dioxide, in handy chart form|
So why do winemakers add SO2 to their wines? It serves two purposes. First, it acts to suppress unwanted yeast and bacteria. If a winemaker is unsure about any aspect of the provenance of their grapes, or if she wants to use a particular cultured yeast, adding SO2 to the freshly-harvested grapes will make sure that the desired yeast does the fermenting.
If SO2 isn't added at this stage, the yeasts and bacteria on the grapes and resident in the winery will do the fermenting. When winemakers want this to happen, great care is taken to ensure that healthy microorganisms are present, and the environment is controlled to maximize their chances. This approach is riskier, but more and more winemakers are opting to take this route and minimize or omit the addition of SO2 at this point in the process. Many claim additional complexity in the finished wine from having the naturally occurring yeasts do the work, but most are simply interested in producing wine with as little human interference as they can.