Back in "the good old days" the typical ash content for most bread flours milled here in the U.S. was in the range of .45 to .48%. This was done to help produce bread with a brighter, whiter crumb color, then came the bread called "Grandma's Bread" made with an unbleached flour so now the finished crumb color was more yellow (actually creamy in color) and all was good as people liked it, so the flour millers decided to "up" the ash content to 0.5% to 0.52% as this allowed them to mill the wheat to a higher extraction rate (more pounds of finished flour from a given weight of wheat) and all remained good by consumer and baker standards as a white crumb structure was no longer the gold standard for bread, in fact the saying "the whiter the bread the sooner you're dead" came to be, and ever since then the ash content has been gradually creeping up primarily as a way for the flour miller to hold the line on cost. Now with some of the hard white wheat varieties we are seeing ash content approaching 0.6%. Ash content used to be used as a quasi measure of protein quality/quantity, this is because as the ash content increases the bran content of the flour also increases slightly, the bran has a small amount of protein attached to it that is mostly non gluten forming, this protein is measured as protein with no distinction between gluten forming and non gluten forming, so we end up with a higher protein content in the flour but all of that protein is not of the gluten forming kind so it was said that while the protein of a long extraction flour was higher it was not necessarily a higher quality protein in terms of gluten strength. You see this all the time when you look at a whole wheat flour containing all of the bran, here we typically see an increase in protein content of about 1% over the same wheat milled as a patent or straight grade flour. Soft wheat flours are still milled to a very low extraction rate to retain the whiter appearance of the flour necessary for many pastry applications, however, with that said, for a good number of years now, some pastry flours have been successfully made from hard wheat varieties, but still with low extraction rates.
In some countries (Mexico for example) it is common to mill the flour to only one extraction rate then use the standard milled flour as a bread flour and then proceed to mill the flour to a finer/smaller particle size for use as a pastry flour.
Tom Lehmann/The Dough Doctor