This is NOT new ... I heard this in the 1980s.
“Alum” (aluminum sulfate) was used in pickles and as a component in baking powder, among other things. I don’t see it in commercial pickles any more, and not all brands of baking powder use it. Aluminum toxicity can cause dementia ...
Alum was used in the early 1800s to "renew" old flour.
Something on the 5-6oz per a sack (280lbs?) of flour.
I didn't know that. I remember as a child, I had a canker sore in my mouth and my mother sprinkled powdered alum on it to deaden the pain.