Gypsum 100g (Calcium Sulphate)
Commonly known as Gypsum, Calcium Sulphate or Burton Salts is used to reduce the pH of the mash and is beneficial in the brewing of bitters. It is also a great water treatment in soft water areas.
Good beer = good ingredients.
Good ingredients = good water, yeast, malts, hops.
Good water = inter alia good mash pH.
Get your mash pH right & the brew is otherwise quite forgiving.