Sulfur in Wine, Demystified

What the sulfur did was turn the ordinarily oxygen-rich environment of an empty wine barrel nearly if not totally oxygen-deficient. On long sea journeys this was really useful, especially for wines with low alcohols and/or a higher Ph. (The more alcohol a wine has, the more protected it is from oxygen’s effects. Similarly, the lower the Ph is, the safer wine is from microbial decomposition.)

Needless to say, this is not all of how we do it today. In an ordinary cycle of turning grapes into wine, we will apply sulfur dioxide at very precise points with extreme caution and great foresight. First, many wineries are likely to add sulfur to the macerated grapes and/or must. Very basically, sulfur protects the must from bacteria and mold that might have been transmitted to the grape clusters either in the vineyard or en route to the winery. With red wine grapes, sulfur also helps the extraction process.

An estimated 500 mL of a sulfur-water (93% water, 7% sulfur) is about average for one ton of fresh grapes – that breaks down to be about 35 mL of pure sulfur per 150 gallons of must. It seems insignificant, but it is very effective in protecting the juice.
No other sulfur is added during fermentation. It would have an arresting effect on the yeast. Most dry wines will go through primary and secondary (malolactic) fermentation without receiving any more sulfur. When the wine has fermented as much as it will, sulfur is then added to protect the wine through aging.

The aging process typically involves at least one racking and blending of the wine before bottling. Some wines undergo more. Small additions of sulfur protect the wine during this practice. At bottling, a wine’s physiology is of the utmost importance for it will not undergo anymore work before a consumer will see it. The wine is now finished, fresh, nearly ready to drink.

As I stated before, the wine’s Ph and alcohol levels – and whether it has been through malolactic fermentation – will contribute to how much sulfur is added prior to bottling. The lower the Ph, and the higher the alcohol, the less sulfur a wine might need … there are exceptions to every rule, for every varietal, for every winemaker.

Once it is bottled, the wine will age and develop – more under a cork closure, less under a screw top or in a bag where there is very little if any oxygen contact. The sulfur both protects the wine from unwanted development and allows the wine to grow old gracefully.