Leavening agents are responsible for the volume in most baked food products.
They are responsible for expanding the air bubbles that have been mixed, creamed, kneaded or whipped into the batter. Leaveners also contribute to a baked goods' taste, coloring and texture. When freezing batters or doughs, the chemical leaveners in them, such as baking powder , baking soda and yeast will lose their potency over time. Baking powder loses its strength after about 6 months. It should bubble vigorously.