Campden tablets, also known as potassium metabisulfite tablets, are a commonly used additive in winemaking, brewing, and other fermentations. They serve several purposes:

1. Sanitization: Campden tablets are used to sanitize equipment, such as fermentation vessels, bottles, and brewing utensils. The tablets release sulfur dioxide gas, which acts as a powerful antimicrobial agent, killing or inhibiting the growth of unwanted bacteria, wild yeast, and other microorganisms. This helps create a clean and sterile environment for fermentation.
2. Preservation: The sulfur dioxide released by Campden tablets is an effective preservative that helps inhibit the growth of spoilage microorganisms in wine, cider, or beer. It helps prevent oxidation and the development of off-flavors and aromas, thus extending the shelf life of the product.
3. Stabilization: Campden tablets can stabilize wines and prevent refermentation. Sulfur dioxide acts as an antioxidant, protecting the wine from oxidation and maintaining its fresh and vibrant characteristics. It also inhibits the growth of residual yeast, preventing any further fermentation or carbonation.
4. Removing chlorine/chloramine: Campden tablets can be used to remove chlorine or chloramine from water. Chlorine and chloramine are often added to tap water as disinfectants, but they can interfere with fermentation and affect the flavor of the final product. Campden tablets neutralize these compounds, making the water safe for fermentation.