Gypsum, also known as calcium sulfate, is added to the brewing or winemaking process to adjust the calcium and sulfate levels of the water used.
In winemaking, gypsum can be used to help clarify the wine and improve the texture and mouthfeel. It can also be used to adjust the pH of the must, which is the crushed grapes and juice used to make the wine. This can help ensure proper fermentation and improve the stability of the finished wine.
Add 1-2 tsp per 5 gallons.