Does bleaching kill the natural yeast in flour? I have read that whole grain flour has more natural yeast than white flour and the rye flour has more than whole wheat.Does anyone know the answer?
to begin their starters, I'd have to say that the bleaching process does not kill all of the yeast cells in the flour. That isn't to say that it doesn't kill some percentage of them, just not all.
In general, whole-grain flours, whether wheat or rye or spelt or whatever, carry more yeast cells than white flours from those same grains simply because most of the yeast cells reside on the outer surface of the kernels. Since you get all of the kernel in a whole grain flour, you get all of the yeasts, too.
I use all of my WW flour for making my poolish and even at 24 hours it adds more flavor than just making WW bread without a preferment. I have settled on a 25% WW bread as the balance that we prefer for taste and texture.
I haven't been able to find any details about how much or why, and I've only found one place that directly states that a bleached flour does have less yeast.
Bleached flour has most of the yeasts killed.
a sour dough starter beginning with a teaspoon each of whole wheat, rye and buckwheat flour and a tablespoon of orange juice and then feed it with unbleached and orange juice.