The chemical leavening effects were accomplished by the activating of a base such as baking soda in the presence of liquid(s) and an acid such as sour milk, vinegar, lemon juice, or cream of tartar. Because these acidulants react with baking soda quickly, retention of gas bubbles was dependent on batter viscosity. It was critical for the batter to be baked quickly, before the gas escaped. The next step, the development of baking powder, created a system where the gas-producing reactions could be delayed until needed.