Baking with Baker's Ammonia (Ammonium Carbonate or Hartshorn)
Baker's Ammonia is a leavening ingredient called for in many old fashioned recipes. It is also called "hartshorn".
Baker's Ammonia is used to make extra-crisp cookies or crackers. Unlike baking powder or soda, it does not leave an alkaline off-flavor in baked goods. It is not used for cakes or other large items because the ammonia gas cannot evaporate from these items.
You will notice an odor of ammonia while baking, but this will quickly dissipate and the baked product will not have an odor or taste of ammonia. Ammonium carbonate turns to 3 gases when heated: ammonia, carbon dioxide, and water vapor. No powder residue remains in your baked goods after baking, but not all of the gases escape, which means a bit of an ammonia odor can linger for a while. Once the product cools, the remaining gases will evaporate.
Because Baker's Ammonia has a tendency to evaporate when exposed to air, it should be stored in a jar with a tight cover. It will not spoil, but will "disappear" if not stored properly.