Sulfur in Wine, Demystified

Everyone’s seen the labeling on wine bottles: “Contains Sulfites.” There is no shortage of opinions as to whether sulfur should be used at all in the vineyard or the winery. Much like anything, with opinions comes confusion. As a wine-industry professional, I would like to dispel some of the myths.

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When it comes right down to it, there is always going to be some sulfur in wine. Sulfur is a natural byproduct of the fermentation process (yes, small amounts of sulfur can be found in bread too) and it is one of the most useful tools a winemaker has. Most basically, sulfur, in fact sulfur dioxide (SO2 – sulfur bound with two molecules of oxygen), acts as a preservative to protect juice and wine from oxidation and the influence of bacteria. Without sulfur, grape juice would turn to vinegar, which is really acidic, and kind of burn a small hole in the ground for the seed inside to be planted. After all, wine is only a byproduct of the arrested breakdown of the grapevine’s seed delivery device.

Inside the grape, the seed has everything it needs to survive what would ordinarily be a cold winter on the ground. The sugars in the pulp of the grape act as food. In the pulp, there are small amounts of water to keep the seed hydrated. The skin of the fruit even acts as a barrier to the environment. However, as that grape breaks down, there are naturally occurring, palatially unflattering things happening. Without the addition of small amounts of sulfur dioxide – far below anything even remotely dangerous – grape juice would ferment and continue breaking down to the point of a sticky sour concentrate.

What sulfur-dioxide does is bind with oxygen and other components commonly found in wine which ordinarily would aid further decomposition of the juice. It also makes unwanted bacterial growth improbable. In other words, it keeps wine fresh. There are other ways to keep wine fresh, such as pasteurization (heating liquids to kill microbes, bacteria, etc), but they are not as effective as even a small addition of sulfur dioxide. There is no way around it (yet). Sulfur dioxide is the single-most useful additive in the wine making process.

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But what are sulfites? When and why is sulfur used? Who was the wise guy that figured out that small additions of brimstone would help keep wine fresh? The truth is no one really knows how long sulfur has been used in wine making. There are brief discourses on sulfur in the letters of Homer and Pliny, but it is also widely accepted that sulfur (in addition to other methods) had been used to preserve food since ancient times. However, the first real document which mentions the specified use of sulfur in wine making is a royal German decree published in 1487.*

Although not widely used by any one region as an industrialized component of its wine practices until the 18th Century in France, not surprisingly in Bordeaux, sulfur had been popularized by Dutch merchants as a means of preserving wines as they traveled from one place to another. A match dipped in sulfur would be burned in empty barrels due to receive fresh wine.