This is a bit of a tricky question because, technically all flour that is used for baking is bleached. Milling a wheat kernel results in a pale yellowish-coloured flour that is left to age for a period of time. Aging the flour makes it better for baking because over time the proteins develop, which strengthen the gluten properties of the wheat. The added effect of this aging process is that the flour oxides and turns whiter or bleaches.
At one point all flour was treated this way. Then, somewhere around the
1800s, scientist came up with another method to age and bleach flour by
adding chemicals to the milled flour. The result was a much reduced
aging period, 48 hours as opposed to 12 weeks, and a much whiter end
product. This process meant less time in a storage unit and therefore
better profits and lower prices for flour. Consumers began to associate
this ultra-white flour with better quality and soon the majority of
flour produced was chemically bleached. The bleached flour that is
chemically produced has a lower protein content then aged flour,
therefore unbleached flour was still used in a lot of commercial baking,
but even this has changed as consumers demanded whiter and whiter
If the product is not labeled either way it has been chemically
bleached. If you read the package you will find a bleaching compound
present, either benzoyl peroxide or some type of chlorine. If a product
is labeled unbleached, it has not been chemically bleached. Recently
there has been a consumer demand for less processed food and therefore
unbleached flour is making a comeback.
Does it Matter?
As to how each works is a matter of opinion. I took a quick survey in
the Test Kitchen and the general consensus is that unbleached or
bleached all-purpose flour act equally in a recipe. I have had the
experience of having to adjust a pastry recipe when it had been
developed with beached flour and I used unbleached instead – but it was a
large scale recipe so possibly in smaller amounts it doesn’t make a
difference. I do think that because of the stronger gluten properties,
unbleached flour is better for making breads and yeast raised products
than bleached flour. I also find that the texture is a bit different,
unbleached flour tends to be a bit clumpier and so I sift if I’m making a
cake or batter.
Is it Really Whiter?
If I’m making something that requires a fine texture I use pasty flour
that for the most part is bleached – I have seen unbleached pastry flour
but it’s not as available as bleached. As far as appearance goes, you
may notice a slightly off white colour to a loaf of bread or cake baked
with unbleached flour but it is pretty minimal.
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