Phosphate aerator is often an ingredient in commercial baking powder and equates to additive 541 in some products ie sodium aluminum phosphate. Some reports estimate that commercial baking powder may be 7-11% aluminum. Now there are Al-free products out there and these tend to use additive 450 (sodium acid pyrophosphate). But if you can't find these brands, here's a homemade alternative. Use 2 tsp per cup of plain flour. Recipe originally in Grassroots magazine.