In wine, a small dose of magnesium sulphate acts as a yeast nutrient, providing the necessary food for a strong yeast growth. The dose rate is half teaspoon per 5 litres of wine together with the yeast. It can also be used together with other nutrients to ensure a healthy yeast colony. If you live in a soft water area, then a pinch of magnesium sulphate in your water will be enough to ensure the correct reactions take place in a healthy fermentation.
Adding 1 teaspoon of magnesium sulphate in 5 gallons of water will roughly increase the magnesium ion levels by about 50ppm and the sulphate levels by about 210ppm.
Mixing both Magnesium Sulphate and Calcium Sulphate together will make a mixture that when added to a beer will give the character of Burton beers. This mixture is usually referred to as Burton Water Crystals.