A common custom to improve flour was to add a small quantity of alum to
a sack of flour--a custom which, it may be hoped, is entirely a thing
of the past. According to Liebig, the action of alum in the process of
bread-making is to form certain insoluble combinations which render
digestion difficult, and detract largely from the value of bread as
food. Professor Vaughan, of the University of Michigan, says: “The use
of alum is an adulteration which is injurious to health. It unites with
the phosphates in the bread, rendering them insoluble, and preventing
their digestion and absorption. In this way, alum, when present,
diminishes the nutritive value of bread. While some gain may perhaps
temporarily accrue to the manufacturer through the covert perpetration
of this fraud, still no good to any one can result therefrom.”