This article is excerpted from one entitled: "Oil Slick" but I am only
sending that portion of the article in which a question is asked about the
differences between bleached and unbleached flour.
Thought you people might be interested in the perspective of this chemist,
Robert L. Wolke
joni
"Oil Slick" (washingtonpost.com) By Robert L. Wolke, Wednesday, May 30,
2001; Page F01
QUESTION: How does bleached flour differ from unbleached flour? Unbleached
wheat flour looks pretty white to me, so why do flour manufacturers bother
with the bleaching step? Does the bleaching process leave any unsavory
residues or leach out any nutrients?
ANSWER Wheat flour is naturally yellowish, but people apparently don't like
yellow flour, except for the semolina used in pasta-making, which isn't
usually bleached. Yellow bread and snow-white pasta wouldn't sell very well.
If given half a chance, though, flour bleaches itself. That is, as it ages
in air, the yellow color is oxidized away. But that takes time and time is
money, so manufacturers speed up the process by using an oxidizing or
bleaching agent such as potassium bromate (in which case the flour is said
to be brominated), chlorine dioxide or benzoyl peroxide. These bleaching
agents aren't mere cosmetics. Flour that has been "aged," either naturally
or by being treated with oxidizers, makes doughs that handle better and
produce better bread.
Unbleached flour generally costs more than bleached flour because it has
been whitened by natural aging, which entails the costs of storage.
Some people are concerned with the intimidating natures of these chemicals.
But they are all unstable and, after doing their jobs, do not remain in the
flour. The bromate, after reacting with the yellow compounds in the flour,
is converted into harmless bromide. Chlorine dioxide is a gas that
dissipates, so there is none of that left in the flour either. Any excess of
benzoyl peroxide would decompose as soon as the flour is heated. The claim
that bleaching flour destroys its Vitamin E is true but empty, because wheat
flour contains negligible amounts of Vitamin E to begin with.
Robert L. Wolke: http://www.professorscience.com is professor emeritus of
chemistry at the University of Pittsburgh and the author, most recently, of
"What Einstein Told His Barber: More Scientific Answers to Everyday
Questions" (Dell Publications, $11.95). Send your kitchen questions to
mailto:wolke@pitt.edu
The Washington Post Company