E503ii - Ammonium hydrogen carbonate
What it is and how it is used
Ammonium hydrogen carbonate — ammonium bicarbonate — is the specific salt behind most of what bakers call baker's ammonia or hartshorn. It is the E 503(ii) form of the ammonium carbonates, and the one usually sold to home bakers as a white crystalline powder with a faint ammoniacal smell straight from the tub.
It decomposes at around 60 °C into ammonia, carbon dioxide and water vapour. Two of those are leavening gases and all three are volatile, so unlike bicarbonate it leaves no salt residue and no aftertaste. That gives it a property no other raising agent matches: it produces a biscuit that is exceptionally crisp and stays crisp, because the extra gas opens the structure and no hygroscopic residue is left to draw in moisture afterwards.
Foods commonly containing it
Crackers and crispbreads, shortbread and thin biscuits, speculaas and lebkuchen, Chinese fried dough sticks, and some ice-cream cones and wafers.
Safety summary
Authorised in Great Britain within the E 503 ammonium carbonates group, which sits in Group I and is permitted at quantum satis. This form is specified as E 503(ii) in the assimilated specifications regulation.
No numerical ADI has been assigned. As with the parent group, decomposition in the oven is complete, so the additive is not present in the finished biscuit.
The practical caution is for the baker, not the eater: the ammonia released during baking is pungent, and the powder should be used in a ventilated kitchen and only in thin, dry goods where the gas can get out.