Ammonia itself is an acrid-smelling gas, usually dissolved in water and used for laundry and cleaning purposes.
But baking ammonia is ammonium bicarbonate, a leavening agent that when heated breaks down into three gases: water vapor, carbon dioxide, and ammonia.
It isn’t used much anymore , if you can even find it, because the ammonia gas can impart a bitter taste if it isn’t all driven off during baking.
Commercial cookie bakers can use it because flat cookies have a large surface area for the gas to escape from.
