Yeast:: This is a raising agent for pastries such as bread, doughnut etc. These pastries are therefore very delicate and should be prepared with care. Hot water may kill the yeast and it may have no further activity and cold water may retard or hinder its action so it is best with warm water for creaming the yeast with sugar. Yeast does not grow once heat is applied therefore allow the bread to rise before putting in the oven