Peter;
It's interesting to note that the reason why I mentioned the Calumet brand baking powder is because it is one of the few that is based on soda and SALP (sodium aluminum phosphate). This is important as SALP has a slower reaction rate than the other food acids so it functions more like yeast in reaction rate rather than reacting very fast as many of the two stage baking powders do. It's also interesting to note that the residual acid component has a significant impact on finished crust flavor, SALP imparts what we call a "biscuit" like flavor (due to the use of SALP based leavening systems in biscuit mixes) that's why we associate the flavor with biscuits, then there is GDL (glucano delts lactone), the residual GDL imparts a decided sweet taste to the crust, and SAPP (sodium acid pyro phosphate) is the leavening system of choice for use in cake donuts, in fact the flavor of a cake donut is that of SAPP. The next time you eat a cake donut run your tongue across the back of your teeth and you'll feel a roughness, this is a phosphate coating from the SAPP. Due to health concerns in Europe SALP is not on the approved food ingredient listing (it doesn't have an "E" number), so CAPP (calcium acid pyro phosphate) is used as a replacement. Aluminum is the issue, at one time aluminum was thought to be associated with Alzheimer's Disease but that was disproved many years ago. CAPP has not been widely available in the U.S. due to the availability of SALP and since they both perform in a similar manner why have two products? We are beginning to see more applications of CAPP though in specialized products where the biscuit like flavor is not desired so if you happen to see CAPP in the ingredient declaration this is the reason. We use SALP in the WRISE product because the biscuit like flavor imparted by any residual SALP is the least offensive in a yeast leavened product. With that said, some refrigerated doughs are made using GDL with the reason being the superior stability offered by the GDL over all of the other food acids. When you have a dough system that is 100% chemically leavened and the chemical leavening system is based on GDL and soda it is incredibly stable until it goes into the oven, the biggest down side to GDL is its low neutralizing value so you need to use significantly more of it to get the same performance you get from SALP and SAPP which in the end means a higher formula cost. In short, when you see GDL being used there has to be a very good reason for using it.
Tom Lehmann/The Dough Doctor