Humco Saltpetre Potassium Nitrate Powder. In West African cuisine, potassium nitrate (salt petre) is widely used as a thickening agent in soups and stews such as Okra soup[22] and Isi ewu. It is also used to soften food and reduce cooking time when boiling beans and tough meat. Salt petre is also an essential ingredient in making special porridges such as kunun kanwa literally translated from the Hausa language as 'salt petre porridge'.