Dave Bell wrote:

>
> Actuall;y, I think I mis-spoke - perhaos Roy / Chembake will step in and
> correct me - I think it's the bicarbonate component, not the acid
> component. Some use Ammonium Bicarbonate, I believe, and probably
> Tartaric Acid...
>
> Dave

Hello Dave,
I would add that
Ammonium bicarbonate is used as the leavening agent( itself ) in low
moisture baked goods such as cookies because of its unique nature to
promote cookie spread while at the same time contributing to leavening:
Schematically
NH4HCO3 +HEAT = NH3( causes the cookie to spread) + CO2 and H2O( both
of which contribute to the leavening effect.
It is not widely used in bakery products due to the water solubility
of ammonia and if the baked product is of high moisture content there
is plenty of residual ammonia left in the baked food making it
unpalatable.

In comparison
sodium bicarbonate does release minimal amount of CO2 by itself as a
leavening agent
unless there is an acid component present such as for example butter
milk, or fruit juice.
Baking soda is best used with acid salt( such as cream of tartar,
calcium acid phosphate, sodium pyrophosphate, sodium aluminum sulfate).

Ammonium bicarbonate is not that stable for use in baking powder
composition aside from being very hygroscopic,
Tartaric acid is too fast to be used in baking powder, cream of tartar
is a bit slower andmore practical for home made baking powder.
Cream of tartar is indeed used to stabilize egg white foams due to its
acidulant effect.