Here in the States we’re used to talking about flours in terms of how much gluten (protein) they contain. Know the gluten percentage of a given flour and you know a fair amount about it: how hard or soft the wheat that it came from, how well it will perform in a cake or a bread, how chewy or tender your finished product will be, and so on.
Europeans gemerally do not talk this way. When they talk flour, they speak of “ash content“, which is also a highly descriptive measure, just very different from gluten content. And while we’re on the subject of Europe, I should point out that European gluten is very different from North American gluten. While ours is stretchy and elastic, theirs is firm and plastic, meaning it doesn’t “snap back” like ours does when it’s stretched. That’s nice, but it’s an advantage that comes with some disadvantages as well. If you’ve ever eaten a French blueberry muffin, you know what I’m talking about.
American flours have a gluten percentage that’s right around 10%. That’s about standard for an all-purpose flour. A few percentage points less and you’re into cake flour territory, a few percentage points more and you’ve got some serious bread flour on your hands.
But what determines how much gluten a flour has? There are two primary factors: the type of wheat the flour was made from and the extraction rate (more on that below). Hard red wheats, which tend to grow in the northern regions of the North American continent, are generally high in gluten. They make great bread. Soft red wheats, which tend to grow best in warmer Southern climates, are low in gluten and are generally better for things like biscuits and cakes.
But of course the way that wheat is milled also has an impact. As I mentioned below in the post on extraction rates, it’s the outer layers of the wheat endosperm (starch reserve) that have the most protein. Thus a high extraction flour is going to have more protein regardless of the type of wheat it came from, and a low extraction will have less.
When you consider that different mills use different varieties of wheats, grind and sift them to varying rates of extraction, and combine the finished flours in varying proportions to produce their final flours, you can see how all this can get confusing very quickly. Milling is a highly secretive business. Every flour company has what it considers its proprietary processes and blends, and few of us on the outside will ever know what they are. Still, now you know a little bit of the how’s and why’s of milling.