Check the label of just about any wine in the United States, and you will find the words, "Contains Sulfites." Sulfites kill bacteria and undesirable yeast (more on that in a moment!) and help to preserve wine by protecting it from oxidation. All wines contain at least some level of sulfites, which are a naturally occurring compound found in grapes and other foods. The warning on the label is added for the benefit of those with a sulfite allergy or sensitivity.
Sulfites are used to sanitize equipment and may be added at any of several different points in the winemaking process including the following:
- Harvesting -- when grapes may be sprinkled with sulfites before they are brought to the winery.
- Crushing -- where sulfites prevent the grapes from fermenting with naturally occurring yeasts.
- Fermentation -- to stop the fermentation process at a desired point.
- Bottling -- to extend the wine's shelf life by preventing it from interacting with oxygen.