SnailsAttack - 28-3-2023 at 03:52
Some baking powders are formulated with sodium aluminum sulphate dodecahydrate (NaAl(SO₄)₂·12H₂O), of all things. Why an aluminum salt? Why not
just citric acid or cream of tartar or something?
Some formulations contain only baking soda and sodium aluminum sulphate as the active ingredients. I'm not 100% sure how the reaction proceeds, but I
believe the net reaction is as follows:
NaAl(SO₄)₂·12H₂O + 3NaHCO₃ -> 2Na₂SO₄ + Al(OH)₃ + 3CO₂ + 12H₂O
I think maybe the benefit of the alum-based baking powder is that it's fairly inert in batter mixtures until the dodecahydrate decomposes due to heat
from the oven, solving the components and allowing them to react. I can't find any sources that specify if this is actually why this formulations is
used, however.
It's worth noting that any unreacted alum, aside from tasting pretty awful, is supposedly a minor neurotoxin and hepatotoxin.
Texium - 28-3-2023 at 07:13
Yep. It’s used in what is referred to as double-acting baking powder. It partially reacts when wetted in the dough, but doesn’t fully react until
heated in the oven. That’s a good thing, because you usually don’t want all your leavening to happen before you bake the dough, or it will not
achieve its maximum airiness. Citric acid or cream of tartar will react too fast at room temperature. Formulations using those are called
single-acting since all the gas formation is complete before the dough is heated.
The potential toxicity of the aluminum is certainly a concern though, so some brands have replaced it with monocalcium phosphate and/or disodium
pyrophosphate.
clearly_not_atara - 28-3-2023 at 07:36
It's cheap, it's legal, and nobody reads the ingredients. What more justification do they need?
The old cost-cutting was just sodium dihydrogen diphosphate (Na2H2P2O7), a poorly soluble (~12% w/w @ rt) sodium salt. It seems like they managed to
find something even cheaper and worse. Of course the original version used cream of tartar. There are recipes for the "original baking powder" using
the original potassium bitartrate (solubility ~0.6% w/w @ rt):
https://www.allrecipes.com/recipe/262231/baking-powder-subst...
Most websites seem to converge on a 2:1 volume ratio of powdered KH tartrate to NaHCO3. The cornstarch seems to be superfluous, but if you're making
powder to store, it may help ensure good mixing and provide volume equivalence. Unfortunately it's difficult to discern the actual mass ratio thereby
applied because powder density is so weird.
In fairness, humans have been using clay pots forever and those definitely contained aluminum, but bound up in silicates, which probably leached only
very small amounts into foods, even highly acidic foods. Alum has been applied for water treatment for a very long time, but aluminum likely
precipitated from the neutral product solution: the solubility of Al3+ at ph 7 is 10-13 molar and remains negligible at any pH > 4.5.
tl;dr: use 1/4 tsp soda + 1/2 tsp CoT to substitute 1 tsp powder if you don't like eating so much aluminum, or buy the kind without aluminum.